UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION CIRCULAR No. 227* June, 1921 PLANT DISEASE AND PEST CONTROL BY W. T. HOENE and E. O. ESSIG ALFALFA Crown Wart = Crown Gall, Urophlyctis alfalfae (Lag.) Magn. ; Stem Rot or Wilt, Sclerotinia libertiana Fcl. or S. trifoliorum Ericks. — Crown wart appears as rounded, irregular tumors near the surface of tin 1 ground, but has no connection with true crown gall. Not seriously destructive in California. Stem rot is due to a fungus similar to or the same as that causing cottony rot of lemons, which attacks various other plants especially leguminous cover crops. Moist and cool weather favor it. Stems rot off near the crown and a white mold with ttered black bodies, often as large as popcorn grains, forms on or in the stems. When the stand becomes too poor, plow and put in some other crop for a few years. Re-level if there are any low spots. Dodder or Love Vine, Cuscnta sp. — Yellowish threads grow up and i atwine the plants, causing serious injury. This is a parasitic plant with minute flowers and with seeds similar in size to alfalfa seeds. Avoid seed in which dodder occurs. The f College of Agriculture of the University of California maintains a laboratory for testing seeds, to which samples may be sent. Small patches may be killed by mowing and, when dry, burning with additional material or kerosene. After- wards resow the spot. Badly infested fields should be plowed up. * This circular is a revised edition of Circular No. 204, Handbook of Plant Disease and Pest Control, by E. E. Smith, E. O. Essig, and George P. Gray, which i3 out of print. The extensive use made of Circular No. 204 and the need for widening its scope have suggested this revision and re-issuance. The authors wish to acknowledge with appreciation the aid of E. E. Smith, E. H. Smith, B. A. Eudolph, H. S. Fawcett, T. Francis Hunt, J. C. Whitten, H. J. Quayle, and W. "W. Mackie, and the Editorial Committee of the Experiment Station, in preparing this circular. t After January 1, 1922, such requests should be directed to the State Depart- ment of Agriculture, Sacramento, California, as at about that time a laboratory will be established by the State Department of Agriculture cooperating with the Bureau of Plant Industry of the U. S. Department of Agriculture. Z UNIVERSITY OF CALIFORNIA EXPERIMENT STATION In the drier sections it is reported that dodder may be killed by keep- ing the field dry for a time, as alfalfa will endure more drought than dodder. Downy Mildew, Peronospora trifoliorum De Bary. — The upper parts of plants turn yellow, the leaves curl somewhat, and their lower sides show a fuzz which turns violet. Affected plants are scattered. Remedies apparently have not been tried in California. Rust, Uromyces striatus Scr. ; Leaf Spot, Pseudopeziza medicaginis (Lib.) Sacc. — Rust shows as powdery brown dots on the lower side of the leaves, and leaf spot as small dark spots, rarely exceeding one- twelfth inch in diameter. Leaf spot is the more common of the two, and is often so abundant as to cause the older leaves to drop. Not often serious or persistent. Worst on weak plants in dry soils under unfavorable growing conditions. Usually disappears after cutting and good irrigation. The hay is valuable for orchard mulch if too rusty for feed. Alfalfa Caterpillar, Eurymus eurytheme (Boisd.). — The caterpil- lars are about one inch long and dark green in color with a distinct and often a pale white or yellow line on each side. They feed on the leaves and may entirely defoliate the plants. The yellow butterflies may be seen in great numbers hovering over the fields. Cutting as soon as the caterpillars appear in destructive numbers, followed by irrigation, is the best method of control. Armyworms, Cutworms, Grasshoppers, etc. — See "General Sub- jects. ' ' Clover Seed Chalcis (Bruchophagus funebris How.). — The small white larva of this insect is just large enough to fill the seed. It occurs in sufficient numbers to greatly reduce the seed crop in most localities in the state. Destroying all the seed heads during winter and the straw after threshing will greatly reduce the infestation for the next year. ALMOND Armillaria, Crown Gall, Sour Sap. — See "General Subjects." Shot-hole, Coryneum heijerinckii Oud. ; Rust, Transchelia punctata (Pers.) Arth. = Puccinia pruni. — Shot-hole is due principally to the peach blight fungus. It causes many fruits to drop and kills small spots on young fruits and leaves. The tissue of the expanding leaves draws away from the dead areas, causing them to drop out and thus leave holes. Rust develops later in the season as small, rusty brown dots on the leaves of almonds, apricots, plums, and peaches. Spray with lime-sulfur 1-10, just as the buds are swelling. Circular 227] PLANT DISEASE AND PEST CONTROL 3 Unfruitfulness. — Usually due to frost or to rain at blooming time, or to lack of a suitable mixture of varieties for cross pollination (most varieties are self -sterile), to lack of bees for carrying pollen, or to weakness from red spider or other injury the previous year. California Peach Borer. — See "Peach." Peach Twig Borer.— See "Peach." Red Humped Caterpillar. — See "Prune." Red Spider or Almond Mite, Bryonia pratensis Garman. — The largest orchard mite, nearly the size of a pinhead ; brownish or greenish with reddish legs, the front pair as long as the body and much longer than the other legs. The bright red, globular eggs are laid in great numbers on the limbs and twigs of the trees, where they remain through the winter and hatch in the spring. Spray the trees in the winter (January and February) with lime-sulfur 1-10 or crude oil emulsion (Formula 18) to destroy the eggs. To control the mite during the growing period of the trees apply dry sulfur, sulfur paste, wettable sulfur sprays (Formula 13 or 14), or lime-sulfur 1-50 as soon as the mites appear in the spring and as often as necessary during the summer and fall. San Jose Scale. — See "Apple." Combined Spraying Lime-sulfur spraying when the buds are swelling will control shot- hole fungus and peach twig borer, and help to destroy San Jose scale and the eggs of the almond mite. Crude oil emulsions will also destroy scale insects, almond mite eggs, and will arrest some of the fungus diseases when applied as a dormant spray. APPLE Blight, Bacillus amylovorus (Burr.) De T. — See "Pear." Remove all worthless apple, pear, and quince trees near apple or pear orchards. Christmas berry, Cotoneaster, and related wild or ornamental plants should be watched for blight. Mildew, Sphaerotheoa leucotricha (E. &E.) Salm. & 8. oxyaaanthae (De C.) De B. — A white powdery growth covers leaves and shoots, causing stoppage of growth and distortion. Where abundant the tree is weakened. Especially serious in foggy sections. Cut out mildewed twigs as thoroughly as possible in winter. Use lime-sulfur for scab spraying or, if scab is not serious, use sulfur paste, 16 pounds to 200 gallons of water (or home-made wettable sulfur spray, Formula 13 or 4 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 14) when petals are falling. Later spraying for mildew may be done with the same material. Sulfur sprays cause injury to apple trees in some sections. Sappy Bark, Polystictus versicolor (L.) Fr. — Bark puffs up in winter about wounds and dries out later, becoming loose and papery. Recurs in succeeding winters, causing death of limbs and general breakdown of trees. Caused by wood decay in the interior of the tree. Avoid large wounds or protect them with a covering of asphalt. See "Wood Decay" under "General Subjects." Scab, Venturia inequalis (Cke.) Wint. = Fusicladium. — Velvety dark moldy patches on young fruit and sometimes on leaves and twigs, rough corky spots on mature fruit, with distortion. Spray with Bordeaux mixture (Formula 9) or lime-sulfur 1-20, just as blossoms open. Again with lime-sulfur 1-35 when petals are falling. Codling Moth, Cydia pomonella (Linn.). — The common white or pinkish worm or caterpillar nearly one inch long is found inside the fruit. For control, spray from two to five times as needed. First spray should be applied as the petals are falling, using 2% pounds powdered or 5 pounds paste arsenate of lead to 100 gallons of water ; the second spraying should be made three weeks later at the same strength. The remaining applications should follow as needed, but should be somewhat weaker, 2 pounds of powdered or 4 pounds of paste arsenate of lead to 100 gallons of water. Cover with a fine, fog- like spray. For a spreader use 1 pound of dry billboard paste to 100 gallons of spray material. (Also see "Spreaders" in "General Sub- jects.") Flat-headed Apple Tree Borer, Chrysobotkris mali Horn. — The full grown larvae or borers are white or pale yellow and vary from one-half to three-quarters of an inch in length. The portion just behind the head is greatly enlarged and flattened, a character which is responsible for the common name. The adult beetles lay eggs on sunburned or other dead areas of the trunk. "Whitewash trunks to prevent sunburn and repel egg-laying. Avoid injuries and wounds. Dig out borers and paint with asphaltum. Fruit Tree Leaf Roller, Archips argyrospila Walker. — The eggs are laid in small, flat, grayish or brownish masses, usually on the new growth near the tops of the trees, in the fall. They hatch in the spring and the caterpillars draw the leaves together into compact rolls in which they live, and from which they wriggle violently if disturbed. When mature the larvae are nearly three-quarters of an inch long, deep green, with the head and thoracic shield dark brown or black. CIRCULAR 227] PLANT DISEASE AND PEST CONTROL 5 The most satisfactory means of control is directed against the eggs, and consists in the use of a miscible oil or crude oil spray (Formula 18) during the winter. Great care must be taken to thoroughly drench the limbs and particularly the tops and outside branches. Some relief may be had during the summer by spraying with 2 pounds of powdered or 4 pounds of paste basic arsenate of lead to 100 gallons of water. Green and Rosy Apple Aphis, Aphis pomi DeGeer and A. mali- foliae Fitch. — Both of these aphids are easily distinguished by their color and the characteristic curling of the leaves, caused by their nu'thod of attack. Control measures are difficult and must be thorough to secure satisfactory results. Late dormant lime-sulfur, 1-10, applied just before the buds open, gives fair results in killing the eggs, but it is better to spray from the time of the bursting of the buds until the leaf buds are one-half inch long with nicotine and soap (Formula 27), or with nicotine and distillate emulsion or miscible oil (Formula 24), or to dust thoroughly with 5 or 6 per cent nicodust. At this time the young stem-mothers may be destroyed as they hatch from the eggs. Red Humped Caterpillar. — See "Prune." San Jose Scale, Aspidiotus pemiciosus Comst. ; Oyster Shell Scale, Lepidosaphes ulmi (Linn.) ; and Other Scale Insects. — The scales of the first are circular and gray, while those of the second are oyster- shaped and similar in color. They occur on all parts of the tree, the first causing a red or purplish stain on the bark and fruit. For the San Jose scale alone, spray with lime-sulfur, 1-10, during the winter months. For a mixed infection of scales, spray preferably with crude oil emulsion (Formula 18), or with distillate emulsion (Formulas 21-23), or with miscible oil. The lighter oil sprays are not so efficient as the crude oil emulsion. Tent Caterpillars and Cankerworms. — See "General Subjects." Tussock Moths, Hemerocampa vetusta (Boisd.) and Notolophus antiqua (Linn.). — The caterpillars are brilliantly colored and clothed with tufts of white hair on the dorsum, with a single long black tuft at the rear and two in front, the latter being responsible for the name "horn worms." The eggs appear as white flat felty masses on the old cocoons and on the limbs of the trees. They are deposited in late summer and fall, but do not hatch until the following spring. The female moths are wingless while the males are normally winged. Con- trol by removing the egg masses during the winter months. Great numbers of the caterpillars may be jarred from the trees and their reascending prevented by applying a band of cotton, wire screen, or tanglefoot around the trunks. Poison sprays are of little use. b UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Woolly Apple Aphis, Eriosoma lanigera (Hausm.). — Easily dis- tinguished by their reddish bodies completely covered with white woolly wax. During the winter months spray with distillate emulsion (Formula 23), miscible oil, or carbolic acid and distillate emulsion (Formula 26a). For the root form, expose the crown of the roots and pour in 4 or 5 gallons of any of the above spray mixtures and recover the roots. Nicotine sulfate (Formula 27) is also effective, or refuse tobacco stems or leaves may be buried in the soil over the main roots during the rainy season. Delicious and Northern Spy rootstocks are somewhat immune and are often used to repel serious attacks of this pest. Of the two stocks the former is more vigorous and easily grafted. Combined Spraying 1. For serious infestations of scale insects, for removal of moss or lichens, and for a general clean-up, use lime-sulfur 1-10 or crude oil emulsion (Formula 18) during the winter. 2. For green, rosy, and woolly aphis, use distillate emulsion (Form- ula 23) or miscible oils just as the buds are beginning to open. .If only the first two are present and scab is a serious pest, substitute late dormant lime-sulfur 1-10. This will assist in the control of the San Jose scale, if present. Combinations of oil sprays for insects with lime- sulfur or Bordeaux mixture for fungus diseases are not considered advisable. 3. For codling moth and scab use 2 pounds powdered or 4 pounds paste basic arsenate of lead to 100 gallons of 1-35 lime-sulfur when petals are falling. For mildew, add 8 pounds of sulfur paste to each 100 gallons of the above and one-half pint of 40 per cent nicotine sulfate for green or rosy aphis. For later infestations of codling moth and scab, repeat above, following recommendations for mildew and aphis if these need attention. In large apple-growing districts obtain advice of local horticultural authorities for modifications of the above. 4. For summer infestations of aphis and red spiders, a combined nicotine and sulfur dust may be applied to great advantage. APRICOT Armillaria, Crown Gall, Sour Sap, Wood Decay. — See "General Subjects." Bacterial Gummosis, Bacterium cerasi Griffin. — Active during moist weather of winter and spring. Attacks buds, twigs, branches, and trunks. Copious turbid or colored gum appears. Affected bark CIRCULAR 227] PLANT DISEASE AND PEST CONTROL 7 when cut into shows moist gumming rot. Cut out diseased bark and disinfect wounds and tools as for pear blight (see " Pear ") . After the first rains the orchard should be frequently inspected and all cankers treated promptly to stop their spreading. Summer treatment is of doubtful value, though gum may continue to flow. Black Heart. — Certain branches die back suddenly in summer with leaves attached and the wood of affected twigs dark-streaked far back into the tree. Peaches, prunes, and almonds are sometimes affected. Avoid excessive irrigation, severe cutting back, or otherwise promoting too succulent growth. Make conditions as normal as possible ; trees usually outgrow the trouble. Investigations now under way will be fully published later. Brown Rot, Blossom Blight, Gumming Twig Blight, Monilia Rot of Ripe Fruit, Sclerotima cinerea (Bon.) Schr. ; Green Rot and Twig Blight, Sclerotinia Ubertiana Fcl. — Blossoms after opening are killed rapidly during damp weather, and older twigs may die back from a few inches to several feet as the result of girdling by the fungus work- ing down the fruit spurs. Small gray powdery tufts of spores usually appear on killed parts immediately and again the following season. Clear amber gum exudes along the boundary of dead and living tissue. Ripening fruit rots rapidly from slight injuries, the rotten fruits be- coming covered with a copious ashy-gray powder. In clusters the disease passes directly from diseased to healthy fruit. All stone fruits are affected. During fall or winter remove the blighted twigs and mummies. The period for effective control by sprays is very short. Spray with lime-sulfur 1-10 when the buds are in full pink or with standard Bordeaux when they are about one-fifth in bloom. For more thorough control apply lime-sulfur or Bordeaux twice between the time when the buds begin to swell noticeably and the time when the bloom is about one-fifth out. Never use lime-sulfur on apricots at any period after the fruit has set. Crude oil emulsion, made with lime- sulfur 1-10 instead of water, may be applied in the pink. Emulsions made with soap and miscible oils with lime-sulfur are dangerous on apricots at any time. Lime-sulfur injury consists in yellowing of the foliage, stunting of the fruit, and disfigurement of the fruit by sedi- ment. There appears to be no way to prevent the occasional occur- rence of sulfur injury with any sulfur spray and Bordeaux is appar- ently as effective a fungicide. Bud Blight, Shot Hole, Fruit Spot, Peach Blight, Coryneum beije- rinckii Oud. — Buds are blackened and killed during winter; spots killed in the opening leaves fall out and leave holes, and small red 8 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION spots with light centers are formed in the young fruit. Spray with Bordeaux or lime-sulfur between November 15 and December 15, and repeat in spring when buds are showing pink. See "Almond" and "Peach." Frost Scabs, Fruit Cracking and Red Specking, Failure of Flower Buds to Open on Strong Shoots, Unfruitfulness of Some Varieties. — Due to climate or obscure causes, and often confused with fungus diseases. Scab, Cladosporium carpophylum Thiim. — Sooty patches to one- half inch in diameter and often confluent form on the fruit, causing drying and cracking. Sprays for brown rot will probably control this. Branch and Twig Borer, Polycaon confertus Lee. — A small elong- ated brown beetle, one-quarter of an inch long, which bores clean round holes at the bases of buds, fruit spurs, and in the forks of small twigs. Often makes necessary severe pruning. The insect breeds in dead oaks and prunings of fruit and other trees. Clean up and burn dead brush and prunings around orchards. Brown Apricot Scale, Lecanium corni Bouche, and Black Scale, Saissetia oleae (Bern.). — Immature scales of both species are brown or grayish, the latter having a distinct " H " on the back. They mature in May and June and are nearly hemispherical ; the former is smooth and brown and the latter black. Control is directed against the im- mature winter forms which occur on the new growth. Spray the trees when dormant, December to February, with crude oil emulsion (Formula 18), distillate emulsions (Formulas 20-23), and miscible oils, all of which give excellent control for both of these scales. Thor- oughness of application is necessary. (See Circular No. 224, Calif. Agr. Exp. Sta., Univ. Calif., Dec, 1920.) California Peach Borer. — See "Peach." Cankerworms. — See "General Subjects." Fruit Tree Leaf Roller.— See "Apple." Peach Twig Borer.— See "Peach." Red Humped Caterpillar. — See "Prune." Shot Hole Borer, Xyleborus xylographies Say and Bark Beetle, Eccoptogaster rugulosus (Ratz.). — Very small beetles boring into the sapwood and heartwood of various fruit trees, preferring usually those not in the best of health. White larvae of the latter may be found during the winter months in sapwood, where they may entirely girdle the trees. Keep the trees growing vigorously ; prune out and burn all dead wood ; destroy all infested branches immediately. Circular 227] PLANT DISEASE AND PEST CONTROL 9 Combined Spraying Dormant strength lime-sulfur (1-10) applied just as the buds are beginning to open, as recommended for fungus diseases, will also con- trol the peach twig borer, remove moss, and give the trees a general clean up. See "Brown Rot" for sulfur injury and for crude oil emulsion added to lime-sulfur. ASPARAGUS Rust, Puceinia asparagi D. C. — Minute yellowish blisters or sori appear on leaves and stems ; these rupture and become rrst-colored and dusty and later black. Plants become pale and bare and are much weakened for succeeding crops. Keep down all volunteer growth in ami about the fields. After cutting stops, irrigate and cultivate to secure vigorous growth, and in about three weeks dust with sulfur while the dew is on, or spray with resin-Bordeaux (Formula 10a) or lime-sulfur containing fish-oil soap for a spreader, or with fish-oil soap and dust with sulfur while still wet. Repeat once or twice, according to tlic severity of the disease in the vicinity. For young fields, dust repeatedly with sulfur as above to prevent infection, beginning when the tops first fully feather out. Asparagus Beetle, Crioceris asparagi Linn. — The beetles are slen- der, one-fourth of an inch long, metallic blue-black with red and yellow markings. The larvae are dull brown or olive green with black head and legs. They feed in great numbers upon the seedlings. Control by clean culture, by cutting and burning seedlings, or by spraying them with nicotine soap spray (Formula 24 or 27). A 6 per cent nieodust also gives quite efficient control. Garden symphylid, Scutigerella calif or nica (Woodw.). — These are small, white, centipede-like animals, scarcely more than one-quarter of an inch long. They live in the damp soil in great numbers and often seriously damage the young asparagus tips before they reach the sur- face of the soil. Clean culture, winter flooding, and crop rotation are the best control suggestions. AVOCADO Pythiacystis Canker, Pythiacystis citrophthora S. & S. — Limb and trunk cankers, resembling gummosis of lemon, but the gummy exudate hardens into a granular whitish mass. Treat as for citrus gummosis (see "Citrus Fruits"). Soil or Drainage Injury. — Certain sickly conditions apparently caused by uneven moisture due to hardpan or other soil defects. Trees 10 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION apparently sensitive to waterlogging of soil and with poor recuperative power after such injury. Branch and Twig Borer. — See "Apricot." Sap collecting in the burrows produces, on evaporation, white powdery masses over the entrances, completely concealing them. Fruit Tree Bark Beetle.— See "Apricot." Spanish Red Scale, Chrysomphalus dictyospermi Morgan. — A pale brown, circular scale, infesting all parts of the tree and serious in greenhouses, but as yet not adapted to orchard conditions. Control by fumigation with hydrocyanic acid gas. Thrips: Lean Thrips, Heliothrips fasciatus Perg., and Greenhouse Thrips, Heliothrips haemorrhoidalis Bouche. — See "Prune." These insects attack the leaves and fruit, causing a shiny, hard discolored surface which has a tendency to check, or crack, and which is covered with numerous fine specks of excrement. BARLEY— See "Grain" BEAN Anthracnose, Collet otrichum lindemuthianum (S. & M.) B. & C. — Spots on leaves, stems, and pods, up to two-fifths inch in diameter, dark-colored, usually with a red border and pinkish in the center. Very rare and unimportant in California. Mildew, Erysiphe polygoni D. C. — Forms a powdery white cover- ing over green parts of the plants; later brownish. May seriously reduce the vitality of the plants. Dust with sulfur at first appearance, or with sulfur nicodust if thrips or aphis are present. Rust, Uromyces appendiculatus (Pers.) Link. — Rust-colored spore masses or sori of pinhead size break through the lower surface of the leaf, with yellow spots above. Affected leaves are weakened and pro- duction decreases. Dust with sulfur at first sign of the disease and keep the surface of the soil dry by cultivation. Wilt or Stem Rot, Corticium vagurn B. & C. = Rhizoctonia, and Fusarium sp. — Many plants die while small from rot near the surface of the soil, others wilt, at different stages. Prepare the soil very thor- oughly, plant as late as possible, avoiding cold and wet weather. Save seed from strong, well matured plants. Bean Aphis, Aphis rumicis Linn. — A small black louse collecting in great numbers on the leaves and tender tips. Use 5 per cent nico- dust or spray with nicotine paste spray (Formula 27a). Circular 227] PLANT DISEASE AND PEST CONTROL 11 Bean Thrips, Heliothrips fasciatus Perg. — A small dark thrips with black and white wings. The larvae are white and pinkish and appear in great numbers on the lower surface of the leaves. Treatment the same as for bean aphis. Bean Weevil, Acanthoscelides obtectus Say. — The adults are short, robust, and about one-eighth inch long. The color varies from gray to brown with pale spots on the dorsum. The larvae work within the stored beans, from which the adults emerge through round holes. Breeding continues in storage. Fumigate in storage with carbon bisulfide, 10 to 30 pounds to every 1000 cubic feet of air space, the amount depending upon the tightness of the container. The temper- ature should be above 70° F. to secure satisfactory control by killing eggs, larvae, and adults. Garden Nematode. — See "General Subjects." Black eyes and Teparys are more resistant than other beans, but are sometimes badly infested. Red Spider or Two-Spotted Mite, Tetranychus telarius Linn. — A very small yellow, pale green or reddish mite, often with two large, or m\ small, dark spots on the body. Feeds on the under side of leaves and often spins a considerable web. If possible keep the beans well irrigated and cultivated and in good healthy condition. Begin sulfur- ing as soon as the mites appear and continue throughout the summer, using 75 parts of dry sulfur to 25 parts finely ground dry hydrated lime. Wireworms. — See "General Subjects." BEET Curly-leaf = Curly-top or Blight. — Transmitted by the beet leaf hopper, Eutettix tenella Baker. Leaf margins curl inward or rarely outward and are much dwarfed and deformed; plants are stunted and easily killed by drought and heat ; young leaves show transparent vena- tion (a clearing of the ultimate leaf vein branches), and a warty con- dition usually develops on the backs of veins on old leaves. Roots often become hairy and show dark rings in cross-section. In the cool districts subject to ocean fogs, the insects do not reproduce abundantly and the disease when established is less injurious. Beets in all other parts of the Pacific slope and of the Rocky Mountains are liable to injury, but in certain regions have been observed to suffer less than in others. Early planting to bring the beets to a good size before the spring inva- sion of the insects from plains and foothills is generally successful 12 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION except in years following early fall rains, which bring up filaree and other vegetation and cause a large number of insects to winter in the cultivated area. Blighted "stechlings" do not produce seed success- fully, although the symptoms many not always be apparent. The sugar beet leafhopper, Eutettix tenella Baker referred to above is wingless in the immature form and winged when full grown. The adults average about one-fourth inch in length. The color varies with the season ; those of the spring brood being pale green ; those of the summer brood are cream colored ; while the winter generations are dark colored with dark markings on the wing covers. The insects are to be found chiefly on the under surfaces of the leaves or between the stems near the crown and produce the characteristic "curly-leaf" described above. Downy Mildew, Peronospora schactii Fcl. — Inner leaves become curled, dwarfed, and covered below with a violet mildew. Develops in moist weather. Remove affected plants and destroy. Rust, Uromyces betae (Pers.) Kuhn; Leaf Spot, Cercospora beticola Sacc. — Rust shows as brownish pustules or sori of pinhead size on the leaves, and leaf spots as dead gray spots, mostly one-sixteenth inch in diameter or smaller, with borders of brown or purple. No treatment needed. Seedling Root Rot, Corticium vagum B. & C. = Rhizoctonia, and Fusarium sp. — Roots are injured and become misshapen and forked; plants are delayed or stunted or die. Make the soil conditions as favor- able as possible for vigorous growth. Replant if the stand is too thin. Armyworms and Cutworms. — See "General Subjects." Beet or Spinach Leaf -miner. — See "Spinach." Grasshoppers. — See "General Subjects." Nematodes.— See "General Subjects." The beet is attacked by two species, the garden nematode, Heterodera radicicola Greef, which produces galls on a number of plants, and the beet nematode, H. schachtii Schmidt, which is confined to sugar beets and does not pro- duce galls. Wireworms. — See "General Subjects." For the sugar beet wire- worm, Limonius calif amicus (Mann.), plow in fall to destroy the pupae. Plant early and practice clean culture. Trap the adults by means of piles of straw and burn in late fall or winter. Circular 227] PLANT DISEASE AND PEST CONTROL 13 BUSH FRUITS (Blackberry, Loganberry, Raspberry) Crown Gall, Bacterium tumefaciens Sm. & T. — See "General Sub- jects." Fruit Mold, Botrytis and Other Fungi. — Avoid mixing bruised or moldy berries with good ones. Leaf Spot, Septoria rubi West, Cane Blight, Leptosphaeria conio- thyrium Sacc. = Coniothyrium. — The former shows small light-colored dead spots with brown and reddish borders. The second causes dead areas on the canes, which are girdled and die. Cut out and burn all affected parts in the fall. Spray with lime-sulfur or Bordeaux during the dormant season. Give proper irrigation and cultivation. Renew old plantings. Sometimes confused with anthracnose, which has not been identified in California. Orange Rust, Gymnoconia inter stitialis (Schlect.) Lagerh. — Bright orange spores cover the lower surface of leaves. Cut off the diseased plants below the surface of the ground and burn. Spray with Bor- deaux mixture to prevent infection of healthy plants. Raspberry Horntail, Hartigia cressoni (Kirby). — The small white larvae are shaped somewhat like the letter "S" and when mature are nearly one inch long. They first attack the tender tips of the new canes and after girdling them and causing wilting they work down the pith to the roots, where they spend the winter. Cut off the young tins as soon as wilting is noticed so as to kill the larvae before they reach the roots. Remove all dead canes in winter, using care to dig out the borers at that time. Rose Scale, Aulacaspis rosae (Bouche). — A pure white scale often found in great numbers at the bases of the old canes. Spray in winter with distillate emulsion (Formula 23) or with miscible oil. Prune out old canes every year, because infestation spreads from them. Serious only where pruning is not practiced every year. Lime-sulfur used as a fungicide gives some control. CABBAGE Armyworm and Cutworms. — See "General Subjects." Scatter poison bran (Formula 4) broadcast over the ground and plants in the evening. Cabbage Aphis, Aphis brassicae Linn. — A small green aphis en- tirely covered with fine whitish powdery wax. Is best controlled by liberal and repeated applications of nicotine-distillate spray (Formula 24) or of nicotine soap (Formula 27). Nicodust gives only partial control. 14 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Cabbage Worm, Pontia rapae (Linn.). — A small green, velvety worm, one inch long when mature, which feeds upon the leaves and destroys the heads. The adults are white butterflies with dark spots on the front wings. Young cabbage plants may be protected by using arsenate of lead, 1 pound of powder or 2 pounds of paste, to 50 gallons of water. This should not be applied after the heads are formed be- cause of possible poisoning of humans. Later control may be accom- plished by applying a nicotine soap spray (Formula 27) . A 5 per cent nicodust also gives very good control when liberally applied. Cabbage Root Maggot, Phorbia brassicae Bouche. — The small white maggots, one-fourth inch long, are found tunneling the roots and they often entirely destroy them. In transplanting, place tarred paper shields around the bases of the plants to prevent infestation, or spray with carbolic acid emulsion (Formula 26) as a repellent. Plow and work the ground thoroughly in winter and spring to expose and destroy the pupae. CANTALOUPE. See Melon CASABA. See Melon CELERY Blight, Cercospora apii Fr. and Septoria petroselini Desm. — Large or small dead spots appear on the leaves and leaf stalks, especially after cutting, and rapid deterioration follows. Spray repeatedly with Bordeaux (Formula 9), especially in moist weather, commencing in the seed bed. Aphids, Rhopalosiphum persicae (Sulz.) and Siphocoryne capreae (Fab.). — Green aphids attacking the stems and leaves of the plants. Spray with nicotine soap (Formula 27) or dust with 5 per cent nico- dust. Celery Caterpillar, Papilio zolicaon Boisd.— The caterpillars are beautifully marked green, black and orange, and feed upon the leaves. Hand pick or spray with arsenate of lead not later than three weeks before harvest (Formula 2). CHERRY Armillaria, Wood Decay, Sour Sap.— See " General Subjects." Gummosis, Die-back.— See "General Subjects." Usually due to shallow soil or too much water or summer drought. Some forms of ClKCLLAK 12:27] PLANT DISEASE AND PEST CONTROL 15 guminosis are caused by specific bacteria (see "Apricot"). Cut out girdled branches below diseased parts and cut out affected areas of bark. Sterilize as in pear blight. See also "Wound Treatment." Leaf and Fruit Spot, Coryneum beijerinckii Oud. — See "Apricot," "Peach," "Almond." Leaf Spot, Coccomyces hiemalis Higgins. — Tiny spots covering most of the leaf surface and becoming fused at the lower edge. Under side shows whitish coating of spores. Not serious as yet. Controlled in the East by Bordeaux mixture, 5-5-50 or lime-sulfur 1-50 adding iron sulphate 1*4 pounds, or dusting with sulfur. Applications as follows: (1) when the fruit is free from the calyx, (2) two weeks later, (3) just after the fruit is picked. Black Cherry Aphis, Myzus cerasi Fabr. — A shiny black aphid with long honey tubes ; appearing in spring and early summer and causing severe curling of the leaves. Spray with nicotine and soap (Formula 27) or dust thoroughly with 5 per cent nicodust as soon as aphids appear. California Peach Borer. — See "Peach." Cankerworms. — See "General Subjects." Cherry Fruit Sawfly, Hoplocampa cookei Clarke. — The small white larvae work within the partly developed fruits of the cherry and plum and are at times responsible for much damage. Their presence is indicated by the dropping of fruit and by the small round exit holes in fruits which are hardly half -grown. The best treatment is the application of arsenate of lead (Formula 2) just when the petals are opening. Cherry Slug, Caliroa cerasi (Linn.). — The common name applies to the small dark green or blackish sluglike larvae which are nearly one-half inch long and which feed upon the leaves in great numbers almost defoliating the trees in some years. Because of their slimy covering they are readily killed by the application of various dusts, such as finely ground hydrated lime, ashes, road dusts, etc., but are best controlled by the applications of 2 per cent or 5 per cent nicodust. The regular arsenate of lead sprays (Formula 2) are also good. Pear Thrips.— See "Pear." Red Humped Caterpillar. — See "Prune." Tent Caterpillars. — See "General Subjects." 16 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION CHRYSANTHEMUM Rust, Puccima chrysanthemi Roze. — Small dark pustules or sori appear on the lower side of leaves. Fertilize and irrigate freely to produce vigorous plants. Aphids (Various Species). — Spray with nicotine and soap (Form- ula 27) or dust with 5 per cent nicodust when the insects appear. Chrysanthemum Gall Fly, Diarthronomyia hypogaea (Low). — The small yellowish or white larvae cause numerous pointed galls on the leaves and stems and seriously injure the terminal buds. Great num- bers of minute slender red eggs are laid on the plants in the spring and early summer, and these may be readily killed by repeated appli- cations of nicotine and soap (Formula 27). Trim the plants to the ground in spring to eliminate hold-over forms. Chrysanthemum Leaf Miner, Phytomyza chrysanthemi Kow. — The injury due to this insect consists in numerous mines on the upper side of the leaves just under the epidermis. These are made by the small whitish maggots, which are easily killed within their burrows by applying one part of 40 per cent nicotine sulfate to 600 parts of water. CITRUS FRUITS (Grapefruit, Lemon, Orange) Blast, Black Pit, Bacterium citriputeale C. 0. Smith. — Blast occurs only in very moist seasons and districts; black pit occurs with blast and also, rarely, in less moist localities. Blast is a watery deterioration of leaves and petioles extending to a shield-shaped area in the twig about the base of the leaf. Leaves die and dry up in place, the twig lesions turn dark, dry up, and heal, and shed off in two or three years. Where several leaves are killed, the twig may be much weakened or die. Black pit consists of dark, sunken spots in the rind of the fruit. They do not decay. Grow bushy, compact trees and avoid severe pruning. Protect the orchard with windbreaks against prevailing rain storms. For northern California conditions, spray from October to December with Bordeaux or ammonia copper carbonate, repeat as soon as the fruit is off or before January 1 with Bordeaux. Blue Mold, Green Mold, Penicillium sps.— Rots the entire fruit, starting in spots and becoming a powdery blue or green, and gray. Avoid even minutest injuries in picking and handling fruit. Brown Rot, Pythiacystis citrophthora S. & S., Cottony Rot, Sclero- tinia libertiana Fcl. — The first produces a firm rot of the fruit with a characteristic odor and slight surface mold. The second produces a rather soft rot with copious white mycelium in which are embedded Circular 227] PLANT DISEASE AND PEST CONTROL 17 black bodies (sclerotia) often larger than rice grains. When the disease is prevalent spray the lower branches and the ground beneath with Bordeaux mixture (Formula 9). Do not allow boxes of fruit to stand over night in the orchard. Use bluestone in the wash water (Formula 12), maintaining a constant strength of 1% pounds to 1000 gallons. Grade out very carefully all orchard infected fruits before storing. Damping Off, Armillaria Root Rot. — See "General Subjects." Gummosis, Phythiacistis citrophthora Smith & Smith. — Copious exudation of gum on the lower part of the trunk. The bark of the affected part dies and the diseased area may continue to spread until the tree is girdled and killed. Cut out all affected bark as soon as dis- covered and treat the wounds with Bordeaux paste (Formula 10) . Do not allow water to stand about the base of trees. In planting keep the point of budding well above ground and never allow the soil to pile up around the trunk. For heavy soil, use trees high-budded on sour orange root. Mottled Leaf. — Add as much organic matter to the soil as possible in the form of green manure crops, bean straw, and manure. See that water penetrates to the subsoil and keeps it uniformly moist. See "General Subjects." Scaly Bark. — Bark at first becomes roughened in a small area; roughening spreads and deepens, finally gumming heavily, encircling the trunk or limb and causing its death. In small early cases on trunks cut out to the wood; in later larger cases scrape off outer layer of affected bark, leaving the inner bark. Cover the wounds with Bor- deaux paste (Formula 10) or other suitable fungicide. Cut off badly affected branches. "Watch all trees very closely in groves where the disease is present and eradicate new cases at first appearance. Do not use Bordeaux if the trees are soon to be fumigated as cyanide is said to render the Bordeaux coating injurious. Aphids (Various Species) .—Use nicotine and soap spray (Formula 27) or a 5 per cent nicodust. Armyworms and Cutworms.— See "General Subjects." Citrus Red Spider, Tetranychus citri McGregor and the Two- Spotted Mite, Tetranychus telarius Linn. — The citrus red spider is bright cardinal red, while the two-spotted mite is yellow, pale green or reddish and often with two or six dark spots on the dorsum. Dust with sulfur or spray with lime-sulfur 1-50 or wettable sulfur (Form- ula 14), or commercial sulfur paste 10 pounds to 100 gallons of water. 18 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION Citrus Thrips, Scirtothrips citri (Moult.). — Small pale yellow in- sects less than one-thirtieth inch long working in blossoms and on leaves and fruit. This insect is most satisfactorily controlled by a 2 per cent solution of commercial lime-sulfur, but may also be con- trolled by using the Government formula for pear thrips (Formula 24) or by applications of 6 per cent nicodust. A combination of mis- cible oil and lime-sulfur is recommended by some for killing the gray citrus scale (Coccus citricola Campb.) and the citrus thrips at the same time. Fuller's Rose Beetle, Pantomorus fulleri (Horn). — A small gray snout beetle three-eighths inch long which attacks young buds and foliage of citrus trees. The adults cannot fly and may be kept off the trees by cotton or tanglefoot bands around the trunks. Mealybugs (Various Species of Pseudococcus) . — These small, flat, oval insects, covered with white mealy material, are well known to most citrus growers. They are difficult to control, but may be most satis- factorily handled by liberal applications of carbolic acid emulsions (Formulas 26 and 26a) and by miscible oils. Washing with water under heavy pressure has proved satisfactory under certain conditions. For the citrus mealy bug, parasites are used with splendid results along the coast. The control of ants is necessary to secure beneficial results from natural enemies (see ' ' Ants") . Scale Insects (Many Species) — Fumigation with hydrocyanic acid gas is best, although some orchardists secure good results, particularly for soft brown and gray citrus scales, by repeated and thorough appli- cations of various strengths of distillate emulsions (Formulas 20 and 23) and miscible oils. CORN Boil Smut or Common Smut, Ustilago zeae (Beckm.) Ung.— Tender tissues of tassel, ear, or stalk swell into large soft masses, which dry out, becoming fragile and filled with black dust. Sometimes gather- ing up and destroying the smutted stalks before the smut balls dry is recommended. Seed treatment is not effective. Often serious in California. Rotation is perhaps useful. Diseased corn trash and manure are infectious. Ear Mold, Diplodia zeae (Schw.) Lev. and Fusarium sp. — The ears mold in the field, the kernels becoming crusted together and light. Sometimes bad in late corn in shallow soil. Use early varieties. Har- vest and cure as early as possible. Avoid over-irrigation. Circular 227] PLANT DISEASE AND PEST CONTROL 19 Head Smut, Sphacelotheca reiliana (Kuehn.) Clint. — Ear and whole top of plant are affected. No grain formed. See "Sorghum." Angoumoise Grain Moth. — See "Grain." Armyworms and Cutworms. — See "General Subjects." Corn Earworm, Chloridea obsoleta (Fab.). — The larvae are nearly two inches long when full grown and vary in color from yellowish to brownish, with longitudinal gray and white stripes and with eight small dark tubercles on each segment. They work chiefly on the corn in the ear, but may also attack the tassels and leaves. Clean up and burn refuse in the field. Plow in fall or early spring to expose and kill the pupae. Repeated dusting of ears with powdered arsenate of lead one part to four parts of hydrated lime gives some relief. Granary and Rice Weevils. — See ' ' Grain. ' ' Grasshoppers. — See "General Subjects." Wireworms. — See "General Subjects." COTTON Bean Thrips. — See "Bean." This insect usually appears on the cotton late in the season, when the injury is not of sufficient importance to justify control. Early infestations should be promptly dealt with. Corn Earworm. — See "Corn." Attacks the cotton bolls. Sweet corn is sometimes planted as a catch crop. Dusting with powdered arsenate of lead or calcium arsenate gives good results. Cotton Leaf Perforator, Bucculatrix thurberiella Busck. — The larvae are pale or dark greenish and less than one-half inch long. When disturbed they wriggle violently. The work consists in per- forating the leaves with very many holes so as to almost entirely consume them. The larvae pupate in small, white ribbed cocoons attached to the leaves or stems of the plants. The adults are white with black dots and other black markings. This insect normally feeds upon wild cotton, but in recent years has invaded the cotton belt of the Southwest, and while it prefers weak plants, it will attack perfectly healthy ones as well. Parasites do much to keep the insect in check but where severe infestations occur dust plants with calcium arsenate alone or with lead arsenate, one part to four parts of hydrated lime. From 20 to 30 pounds are sufficient for an acre of cotton. Red Spider or Two-Spotted Mite, Tetranychus telarius Linn. — See "Bean," 20 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION CUCUMBER Mildew, Erysiphe dehor earum D. C. = Oidium. — Fine white my- celium covers the leaves. Dust with sulfur at first appearance or with sulfur nicodust if the melon aphis is also present. Flea Beetles (Various Species). — Small flea-like beetles which jump quickly and eat small holes in the leaves. Bordeaux mixture (Form- ula 9) as a repellent is the best control measure. This treatment is also recommended for mildew. Garden Nematode. — See ' ' General Subjects. ' ' Melon Aphis.— See " Melon." Red Spider or Two-Spotted Mite.— See "Bean." Western Twelve-Spotted and Striped Cucumber Beetles, Diabro- tica soror Lee. and D. trivittata Mann. — The former is a small green beetle with twelve black spots on the back and is often mistaken for a ladybird; the latter is a brown beetle with three black lines on the dorsum. The white larvae feed upon the roots and may be controlled by pouring on the roots a cup of 40 per cent nicotine sulfate diluted 1 to 1000 parts of water. Bordeaux mixture (Formula 9) is of con- siderable value as a repellent. Arsenate of lead (Formula 2) may also be used with good effect. CURRANT, GOOSEBERRY Mildew, Sphaerotheca mors-uvae (Schw.) B. & C. — A fine white mycelium grows over the young leaves and shoots and checks their development. Serious on some varieties. The best treatment is to spray with lime-sulfur 1-33 when buds commence to open and two or three times thereafter at intervals of 10 to 14 days. "Where serious cut and burn diseased tips of canes while dormant, as the fungus win- ters in them (from U. S. D. A. Farmers' Bull. 1024). In California, where resistant varieties are used, a dormant spray of lime-sulfur 1-10, followed by dusting with sulfur when the disease first appears, has generally been effective. Currant or Gooseberry Fruit Fly, Epochra canadensis Loew. — Small white maggots in the fruit at picking time. Cultivate thoroughly during the fall, winter, and spring months to expose and destroy the hibernating pupae. Flat-Headed Apple Tree Borer.— See " Apple." Imported Currant Borer, Aegeria tipuliformis Clerck. — White caterpillars nearly one inch long working down the middle of the stalks and into the roots of the plants. Cut out and burn all dead and in- fested canes during winter and remove the borers. ClRCLLAR 227] PLANT DISEASE AND PEST CONTROL 21 Red Spider or Two-Spotted Mite, Tetranychus telarius Linn. — See "Bean." Dust with sulfur or spray with wettable sulfur (Formula 14) or sulfur paste (Formula 13). San Jose Scale. — See "Apple." Combined Sprays The sulfur sprays will control both the mildew and the red spider. DAHLIA Mildew, Erysiphe sp. — White spots spread over lower leaves. Not serious. Dust with sulfur. Bean Aphis. — See "Bean." Western Twelve-Spotted Cucumber Beetle. — See "Cucumber." DATE Date Palm Scale, Parlatoria Uanchardii (Targ.). — A small gray and white scale, less than one-sixteenth inch long, often occurring in great numbers on the leaves. It may be controlled by cutting away and destroying all the leaves, burning over the trunk with a gasoline torch. Offshoots are cleaned up by heavy fumigations with hydro- cyanic acid gas. This insect is quarantined by the Federal Horticul- tural Board, and young plants may be obtained only from uninfested territory. Dried Fruit Beetle.— See "Prune." Indian Meal Moth. — See "Prune." This insect is a serious pest of dried dates, of which small amounts are preferably put up only in insect-proof containers to prevent infestation. Marlatt Scale, Phoenicacoccus marlatti Ckll. — A red-bodied, cot- tony covered scale, considerably larger than the Date Palm Scale. It is chiefly found in the unfolding leaves, often so protected as to be almost impossible of control. Fumigating and burning over the trunks and treating liberally with carbolic acid and oil emulsions give some control, but eradication on a tree once thoroughly infested is appar- ently impossible. This pest is also under federal quarantine, and new plants may be obtained only from uninfested territory. Red Spider.— See "Citrus." 22 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION FIG Smut, Sterigmatocystis ficum (Reich.) Hen. — The inside of the fig becomes a powdery, purple mass. No remedy known. Souring and Splitting. — Due to unfavorable atmospheric and soil moisture conditions. Choose suitable localities and regulate the soil moisture with greatest care. At least two canker diseases are known in California, and twig blight is caused to a limited extent by Sclerotinia libertiana and Botrytis cinerea. None of these appears to be serious. Branch and Twig Borer. — See "Apricot." Mediterranean Fig Scale, Lepidosaphes ftcus (Sign.). — Scales re- semble small oysters and infest the limbs, twigs, leaves, and fruit. Spray with distillate emulsion (Formula 23), miscible oil or crude oil emulsion (Formula 18) during the winter when the trees are dormant. Nematodes. — Becoming increasingly serious. No remedy known. See "General Subjects." Pomace or Vinegar Fly, Drosophila melanogaster Meigen. — Small, slender, whitish maggots and brown or orange-colored flies one-tenth inch long, often occurring in great numbers in figs on the trees and on the drying trays. Attacks only soured fruit, but is neither respons- ible for the souring nor injurious to sound fruit. GRAIN (Barley, Oats, Wheat) Rustj Puccinia sps. — Pustules of pinhead size, round or elongated, break through the surface of leaves and stems ; mostly reddish at first and dusty, later black. Serious in heavy grain in moist situations or seasons. No remedy known but resistant varieties may be used. Smut, Ustilago sps. and Tilletia sps. — Mature grain has black con- tent and gives off characteristic odor. Seed of wheat, barley, oats, Sudan, millet and sorghum should be carefully cleaned of smut balls, weed seeds, and small, cracked, and inferior grains before treating. The smut balls in wheat and smut masses in barley may be cleaned out in fanning mills or floated out in water and skimmed off. Place the cleaned seed in half -filled sacks tied at the end. Immerse these sacks for three or four minutes in a bluestone solution made by dissolving 1 pound of bluestone in 5 gallons of water (Formula 11). Drain the sacks until dripping no longer occurs, then dip them for three minutes in a milk of lime made by slaking 1 pound of quicklime in 10 gallons of Circular 227] PLANT DISEASE AND PEST CONTROL 23 water. The lime prevents injury to the germ from bluestone. If quick- lime cannot be secured, air-slaked lime, 1 pound to 8 gallons of water may be used. After this treatment the grain should be spread out to dry, after which it may be planted or stored. Oats are especially sensitive to bluestone, and for them it is better to use a solution of formaldehyde, 1 pound to 40 gallons of water, for ten minutes. After this no lime dip is needed. Barley is more sensi- tive than wheat and should always be lime-dipped after treatment with bluestone. Seed scratched or injured in threshing should be limed after dip- ping in bluestone solutions. Scoured seeds should not be dipped in any fungicidal solution. Seed wheat and barley to be sown in dry ground or to be stored longer than 48 hours must not be treated with formaldehdye, as severe injury may follow. If foggy or rainy weather is liable to interfere with the proper drying of lime-treated seed, heating injury may be avoided by soaking the seed for 10 or 15 minutes in water before dipping in the bluestone solution. The lime dip may then be omitted. Loose smuts of wheat and sorghum cannot be controlled by the above treatment. Loose smuts of oats and barley are destroyed by formaldehyde solution (1 pint to 30 gallons of water) soaking for 10 minutes. Kernel smut of sorghums and Sudan grass is controlled by soaking the seed in formaldehyde solution, as above, for 30 minutes for grain sorghums and 60 to 90 minutes for sweet sorghums and Sudan- Ergot of rye and rye grass is controlled by floating off the ergots in a strong brine solution (40 pounds salt in 25 gallons water) and rinsing with clear water, or by holding the seed for a year before sowing. Copper carbonate dust intimately mixed with wheat seed at the rate of 2 ounces per bushel is a new and promising fungicide for control of bunt. Angoumoise Grain Moth, Sitotroga cerealella Oliv. — A small tawny moth found in granaries. The pale yellow caterpillars feed within the kernels of stored grain and corn, escaping through a round hole. Control measures are the same as for the granary and rice weevils (see below). Aphids (Many Species). — Aphids often seriously attack grain. Control methods are usually too costly to be practicable. Cutting is often resorted to in order to save that part of the crop. Armyworms and Cutworms. — See "General Subjects." 24 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Granary Weevil, Calandra granaria Linn., and Rice Weevil, C. oryzae Linn. — Small brown weevils not over one-sixth inch in length, attacking the grain in storage. Fumigate with carbon bisulfide, 10 to 30 pounds to 1000 cubic feet of air space, according to the tightness of the container. The temperature must be at least 70° F. for satis- factory results. Hydrocyanic acid gas may also be used as a fumigant, in which case from 1 to 4 ounces of pure sodium cyanide to 100 cubic feet of air space should be used. Heating the grain to 125° F. for several hours will kill all the weevils. Keeping the grain dry and well ventilated will largely prevent weevil attack in storage. Grasshoppers. — See ''General Subjects." GRAPE, RAISIN Crown Gall = Black Knot, Bacterium tumefaciens S. & T. — May be treated with some success. Not usually very injurious. See ' ' Gen- eral Subjects." Little Leaf, Apoplexy, Obscure Diseases. — See "Physiological Diseases" under "General Subjects." Mildew, Uncinula spiralis B. & C=U. necator (Schw.) Burr. — White mycelium spreads over young leaves, canes, and fruits, checking growth ; the leaves are deformed and may drop ; the surface of the fruit hardens and darkens and the fruit often cracks, or may drop. Dust with sulfur when the shoots are about 6 inches long and again just before the blossoms open, being careful not to miss a single leaf. If the vines were affected the previous year do not wait until the mildew appears. In cool or moist locations a third sulfuring when the grapes are as large as peas and a fourth when they are two-thirds grown may be necessary. In these later treatments the sulfur should be dusted only on the fruit and the centers of the vines. If the larvae of leaf-hoppers are present use nico-sulfur instead of sulfur. Achemon Sphinx Moth, Pholus achemon (Drury). — Large green and pinkish caterpillars with oblique whitish bars on the sides. Often abundant and doing great damage by stripping the vines. Adult moths dull gray with brown marks and pink hind wings. Spray vines with arsenate of lead (Formula 2), to which is added 1 pint of 40 per cent nicotine sulfate to every 200 gallons, or dust with powdered arsenate of lead, 1 part to 4 parts of hydrated lime or flowers of sulfur. Armyworms and Cutworms. — See "General Subjects." Circular 227] plant DISEASE AND PEST CONTROL 25 California Grape Root Worm, Bromms obscurus (Linn.). — The adult beetles are black or brown and three-sixteenths inch long. They eat long slender holes in the leaves. The small white grubs feed on the roots of the vines. Cultivate thoroughly close to the vines during the winter to kill hibernating larvae. As soon as beetles appear in the spring spray with arsenate of lead, 6 pounds of paste or 3 pounds of powder to 100 gallons of water, or dust with one part of powdered arsenate of lead to four parts of hydrated lime or sulfur. Dried Fruit Beetle. — On raisins, see "Prune." Grape Leaf -hopper, Erythroneura comes (Say). — The immature forms or nymphs are white or pale yellow, while the adults are pale yellow with numerous small reddish marks all over the dorsum. All forms feed on the under side of the leaves, causing them to turn yellow and drop prematurely. Clear weeds and refuse from around the vineyards and practice clean culture to reduce the number of over- wintering adults. Before the young nymphs develop wings spray thoroughly with nicotine and soap (Formula 27), or with the follow- ing: 40 per cent nicotine sulfate, 1 pound ; liquid soap, % gallon (hard soap, 2 pounds) ; water, 200 gallons. The young and adults may also be killed by thoroughly dusting with a 10 per cent nicodust, or a 6 per cent nicosulfur dust, which latter will also control mildew. Grape Phylloxera, Peritymbia vitifoliae (Fitch). — The presence of the phylloxera is indicated by weak and dying vines, and usually occurs in spots. The insect is a minute, yellow louse which feeds upon the roots. To disinfect cuttings or rootings before planting, dip in hot water 122° F. for five minutes. For permanently resistant vines, graft European varieties on certain American roots (see Circular No. 226, Calif. Agr. Exp. Sta., Univ. of Calif., Dec, 1920). Grasshoppers. — See "General Subjects." Indian Meal Moth. — On raisins, see "Prune." Mealybug, Pseudococcus maritimus Ehrh. = P. bakeri Essig. — Easily distinguished by the small oval, flat bodies covered with white cotton-like wax and by the cottony egg masses among the bunches of grapes. Difficult of control, but best results have been obtained by burning sulfur under a tent over the vines. (See Monthly Bull., Cal. State Dept. Agr., Sacramento, Vol. IX, p. 26, 1920. Also see "Pear.") HOLLYHOCK Rust, Puccinia malvacearum Mont. — Prominent red sori or pus- tules push out on the lower surface of the leaves and on petioles and stems, often causing distortion. Fertilize and water freely to promote vigorous growth. 26 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION The Painted Lady Butterfly, Vanessa caryae Hubn. — The yellowish or black spiny caterpillars, which are about one inch long, feed upon the leaves, which they draw together with webs for protection. Con- trol is best accomplished by using 40 per cent nicotine sulfate, 1 part to 600 parts of water, and spraying the plants thoroughly. HOP Hop Aphis, Phorodon humuU (Schr.). — A pale green aphid at- tacking the young shoots and leaves. Dust thoroughly and as often as necessary with 5 per cent nicodust or spray until injury ceases with nicotine and soap (Formula 27). Hop Flea Beetle, Psylliodes punctulata Mels. — A small green or bronze metallic beetle, one-tenth inch long, attacking the foliage. Jumps quickly when disturbed. The most efficient method of control consists in putting tanglefoot bands around the bases of the vines and around the poles. These not only prevent the beetles from climbing the vines but catch great numbers of them. Red Spider or Two-Spotted Mite.— See "Bean." LOQUAT Pear Blight, Bacillus amylovorus (Burr.) Detoni. — Limb and body blight is sometimes very severe. See ' ' Pear. ' ' Scab, Fusicaladium eryobotryae Sciala. — Eesembles scab of pear and apple, but is more injurious to expanding foliage. See "Pear." Green Apple Aphis. — See "Apple." San Jose Scale. — See "Apple." MELON (Casaba, Cantaloupe, Pumpkin, Squash, Watermelon) Wilt, Fusarium sp. — Well grown watermelon plants wilt and die, leaving the field nearly bare. Plant on fresh soil. Melons cannot be grown for several years on infected ground. Other melons are not often, if ever, affected in California. Flea Beetles. — See "Cucumber." Melon Aphis, Aphis gossypii Glover. — A small, dark green louse occurring in great numbers on the plants and doing great damage. Destroy first infested plants as soon as discovered in spring, or spray with nicotine sulphate, 40 per cent, 1 part to 1000 parts of water. A 5 per cent nicodust also gives very good results and is much more easily and quickly applied. Nematode. — See "General Subjects." Circular 227] PLANT DISEASE AND PEST CONTROL 27 Squash Bug, Anasa tristis De Geer. — The young hugs are gray with black antennae, legs, and thorax, the adults of a uniform dull grayish-brown above, mottled yellowish beneath, and about three- quarters inch long. Control measures should be directed against the immature forms, and consist in the use of one part of 40 per cent nicotine sulfate to 600 parts of water. A 10 per cent nicodust kills many. Hand picking the adults in the spring is successful in small gardens. Western Twelve-Spotted and Striped Cucumber Beetles.— See ' ' Cucumber. ' ' NURSERY STOCK Failure to Grow After Planting in Orchard. — Very rarely due to specific disease. Usually caused by freezing, drying, or water soaking of trees before or after planting ; planting too deep ; cold, wet, or hot weather after planting ; or some other condition unfavorable to growth. Buy from the nearest reputable nursery. Pay for good trees and see that they are handled and planted carefully. Replant all that do not grow well the first season. Lemon Brown Rot or Pythiacistis, Pythiacistis citropJithora S. & S. — Dead spots up to several inches long develop on the trunk, mostly above the bud union. Caused by soil infection in very wet conditions. Spray trees with Bordeaux mixture before digging and after healing in. Soil for healing in should be well drained or under cover. Active only in very wet seasons. Nematode, Crown Gall. — Very carefully avoid planting affected trees. If a large percentage of a plot of trees is affected, those appar- ently healthy are of doubtful value. See "General Subjects." Citrus Trees. — For scale insects, defoliate and fumigate with hydro- cyanic acid gas. Rejecting infested stock is the only safe procedure. Deciduous Trees. — For borers and other insects, fumigate with hydrocyanic acid gas. Rejecting infested stock is the only safe pro- cedure. ' ■ ' •' ' OAT. See Grain OLIVE Peacock Spot, Cycloconium oleaginum Cast. — Blackish round spots, one-eighth to one-quarter inch in diameter, on the surface of green leaves but not killing the darkened area. Is apparently of very slight importance in California. Armillaria, Wood Decay.— See "General Subjects." 28 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Die-back === Exanthema. — Bushy phase characterized by repeated death of terminal buds and branching out below ; leaves show deform- ities. In die-back phase there is usually dropsy-like puffing of bark on branches and limbs and unusual prominence of lenticels in the smooth bark, with dying back. Secure uniform moisture and good drainage. Add organic material to soil by green manure crops, mulch, or manure. Replace olives with plums, peaches, or other crop where die-back is very bad. See "Physiological Diseases," under "General Subjects. ' ' Dry Rot, Bitter Pit. — Dry spots appear in the flesh of the fruit. See "Physiological Diseases," under "General Subjects." No effec- tive treatment known except good general care. Olive Knot = Tuberculosis, Bacterium savastanoi E. F. Smith = Pseudomonas oleae. — Rounded rough swellings, from very small up to several inches in diameter, appear on twigs, limbs, trunk, or roots, mostly at leaf scars or wounds, also rarely on fruit pedicles and leaves. Cut out thoroughly at first appearance and disinfect. See "Pear Blight" and "Crown Gall." The Mission is more resistant than the Manzanillo or some oil varieties. Black Scale, Saissetia oleae (Bern.). — See "Apricot." Attacking chiefly the twigs. Spray with distillate emulsion (Formula 23) or miscible oil, December to February. Branch and Twig Borer, Polycaon confertus Lee. — See "Apricot." This is often a serious pest of young olive trees. Ivy or Oleander Scale, Aspidiotus hederae Vail. — A small circular, flat, gray scale occurring on the leaves and fruit, sometimes causing discolored spots on the ripening olives. Control as for black scale. Olive Bark Beetle, Leperisinus californicus Swaine. — The small white larvae work in the cambium layer just under the bark and the adults bore small, round exit and entrance holes through the bark. Occurs in the southern part of the state. Burn prunings and remove all dead and infested portions of the trees. ONION Downy Mildew, Peronospora schleideni Ung. — Areas on leaves or stems show a violet tinted fuzz. These areas rapidly fade and collapse if the weather is moist, and the disease may spread rapidly. Not suc- cessfully controlled in wet seasons. Bordeaux mixture found useful in some cases ; it should be used with resin fish-oil soap or other spreader. See "Spreaders," pp. 68-69, also "Asparagus." Armyworms and Cutworms. — See "General Subjects." ClECULAR 227] PLANT DISEASE AND PEST CONTROL 29 Onion Maggot, Hylemyia antiqua Meig. — Small, white maggots attacking the onions beneath the ground. Practice clean culture and destroy all refuse onions in the fall. Plow and cultivate thoroughly during winter and spring. Considerable protection is gained by spray- ing the plants repeatedly with carbolic acid emulsion (Formula 26, diluting stock solution 1 to 40). Onion Thrips, Thrips tabaci Lind. — Minute, slender, pale yellow insects occurring in great numbers on the leaves, causing them to turn gray and wither. Spray with 1 part of 40 per cent nicotine sulfate to 200 parts of water or apply 5 per cent nicodust. Wireworms. — See "General Subjects." PEA Bacterial Blight or Bacteriosis, Pseudomonas pisi Sack. — Exten- sive, watery, olive-green blisters appear on stems and leaves in wet weather following cold. Many affected areas dry up, others kill the stem. In some wet situations practically every plant has been killed. Control probably the same as for blight. Blight, Mycosphaerella pinocles Berk. & Blox = Ascochyta. — Sunken dead spots form on pods, leaves, and stems, one-quarter inch or less in diameter; center of spot on pod becomes gray or pinkish, with a dark border ; on leaf and stem spots are more often merely dark. Young stems may be killed. Experiments indicate spraying is imprac- tical. Keep pea crop and diseased material off the land for two years. Seed infection rare in California. Avoid too low, wet land. Mildew, Erysiphe polygoni D. C. — Powdery white growth spreads over the foliage, injurying plants. Troublesome in summer or when rains are light or lacking. Dust with sulfur on first appearance or nicosulfur dust if aphids are abundant, and repeat if necessary. Armyworms and Cutworms. — See "General Subjects." Pea Aphis, Macrosiphum pisi (Kalt.). — A large green aphid at- tacking the terminal shoots and leaves of the vines. It is difficult of control because of the expense involved, but can be killed by repeated applications of a 10 per cent nicodust or a nicotine spray (Formula 27a,) or a 6 per cent nicosulfur dust to also control mildew. Pea Weevil, Bruchus pisorum Linn. — A small gray and white weevil attacking the pea, much as the bean weevil attacks the bean, but the pea weevil infests the peas in the field and the adults do not emerge until the following spring. Unlike the bean weevil, however, it never reinfests stored peas. Treatment is the same as for bean weevil. See "Bean." 30 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION PEACH Armillaria, Wood Decay, Crown Gall, Nematode. — See ' ' General Subjects." Blight, Coryneum beijerinckii Oud., Curl Leaf, Exoascus deformans Fcl. — In blight; buds are killed during winter, sunken round spots are killed in one-year twigs, and in spring a shot-hole effect appears on leaves; later the twig spots gum profusely and gradually heal over unless the twig is killed. In curl leaf, young leaves and sometimes shoot tips become much thickened and ruffled. Later they become powdery, fade and drop early. The tree is weakened through loss of foliage. Spray with Bordeaux (Formula 9) or lime-sulfur 1-10 be- tween November 15 and December 15. Repeat with lime-sulfur as blossoms begin to open. Peaches can not be sprayed after leaves ap- pear with these sprays without serious injury. Brown Rot, Sclerotinia cinerea (Bon.) Schrot. — Sometimes im- portant in causing decay of late ripening fruit in moist regions near the coast. See "Apricot." Control for fruit rot not developed in California. Green Rot. — See "Apricot." Little Leaf. — See "Physiological Diseases" under "General Sub- jects." Powdery Mildew, Sphaerotheca pannosa var. persicae (Wallr.) Lev. — See "Apple Mildew." Also attacks the fruit. Spray with lime-sulfur as for curl leaf. Prune to thin foliage. Dust with flowers of sulfur at first indication of mildew and repeat as necessary. Black Peach Aphis, Aphis persicae-niger Smith. — A shiny black aphid occurring in great numbers on the young tender shoots. Spray with nicotine and soap (Formula 27) or dust with 5 per cent nicodust as soon as the insects appear. Black Scale.— See "Apricot." Branch and Twig Borer, Polycaon confertus Lee. — See "Apricot." Brown Apricot Scale. — See "Apricot." California Peach Borer, Aegeria opalescens Hy. Edw. — White cat- erpillars attaining one and one-half inches in length which burrow under the bark at the base of the trees, often extending their tunnels down into the bases of the main roots. Often serious, as they may completely girdle the trees. Dig out the worms carefully in the fall and spring and paint over the wounds with a good asphaltum paint. Cankerworms. — See "General Subjects." Flat-Headed Apple Tree Borer.— See "Apple." Circular 227] PLANT DISEASE AND PEST CONTROL 31 Peach Rust Mite, Phyllocoptes cornutus Banks. — A microscopic mite causing a silvering of the leaves. Spray in winter when the trees are dormant or when buds swell in the spring with lime-sulfur 1-lb to kill mites hibernating in buds. Peach Twig Borer, Anarsia lineatella Zeller. — A small, dark- reddish caterpillar, scarcely one-half inch long, which burrows into and kills the young tender tips of the twigs and, later on, may infest the fruit to some degree. The minute young forms hibernate in small cells in the bark and are effectively killed in the early spring of the year with lime-sulfur 1-10 applied just as the blossom buds begin to open, which is before the larvae are able to enter the expanding leaf buds. Red Spider.— See "Almond" and "Prune." San Jose Scale. — See "Apple." Shot Hole Borer.— See "Apricot." Tent Caterpillars. — See "General Subjects." Wheat Thrips, Frankliniella tritici (Fitch). — This minute orange and yellow thrips often does considerable damage to the young fruit at blossoming time and later. For control see pear thrips under "Pear." Combined Spraying Two applications of lime-sulfur as recommended above will control all of the usual diseases and pests of the peach in California which can be reached by any spray treatment, but lime-sulfur has occasion- ally been reported as causing injury when applied in the bloom. PEAR Black End. — Is presumably a physiological disease comparable to blossom end rot of tomatoes. No recommendation as yet except to give good care, especially as to drainage. Black Leaf.— See "Sour Sap" under "General Subjects." Blight, Bacillus amylovorits (Burr.) Detoni. — Tender growth be- comes watery, darkens rapidly, wilts, and dies ; usually minute beads of viscid material exude ; they dry in the same form and show a solid mass of bacteria when moistened in water ; in heavier bark the exudate may be more copious, or lacking ; the diseased tissue may be recognized by cutting into it. Watery, reddish or somewhat dark streaked areas indicate blight. Any succulent part of the top may be attacked, or the root. Cut out all affected parts very thoroughly. Work especially on "hold-over" in large limbs, trunks, and roots during the winter. 32 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Disinfect tools and cuts freely. A new system is being largely used in which only the outer bark is cut away, leaving the cambium. Keep close watch of the surface to check new development of infection. Mercuric cyanide and corrosive sublimate, one part of each to 500 of water (Formula 28a), is widely used for disinfection. Keep all suckers and spurs off of root and body. In new plantings in blight regions, top-work on resistant varieties. Surprise, Ussuriensis, and others are being used and promise well. Scab, Venturia pyrina Aderh. = Fusicladium. — Dark velvety mold patches appear on young fruit and leaves; badly affected fruit drops, but much remains, the dark areas becoming hard and rough and often cracked, deforming the fruit. Spray with lime-sulfur 1-12 or Bordeaux (Formula 9) just as the cluster buds are opening. Repeat when the first blossoms are open. Baker's Mealybug, Pseudococcus maritimus Ehrh. = P. bakeri Essig. — Small, oval, flat insect less than one-quarter inch long and covered with white powdery wax and normally with several white, tail- like filaments nearly half as long as the body. The egg sacs look like small masses of cotton. The insects occur under the bark, on the under side of limbs, in cracks, wounds, and in the blossom end of the fruit. Control measures are difficult and consist of repeated applications of crude carbolic acid and distillate emulsion (Formula 26a) during the winter months and until the buds begin to open in the spring. Scrape the rough bark from the trunks and larger limbs so as to expose the mealybugs to the spray. If the fruit is infested, spray during the summer with water under heavy pressure to wash the bugs away. Branch and Twig Borer. — See "Apricot." Brown Apricot and Other Soft Scales. — See "Apricot." Cankerworms. — See "General Subjects." Cherry or Pear Slug. — See ' ' Cherry. ' ' Codling Moth. — See "Apple." The control of this insect on pears is not so difficult as on apples, but thorough work is necessary to insure clean fruit, particularly in districts where large acreages of pears are grown. Fruit Tree Roller.— See "Apple." Green Apple Aphis. — See "Apple." Italian Pear Scale, Epidiaspis piricola Del G. — A small gray cir- cular scale, the body being dark red, usually occurring under the moss or old bark; but it may cover the trunks and all of the main branches of the tree. Causes sunken areas in old limbs and greatly Circular 227] PLANT DISEASE AND PEST CONTROL 33 weakens the tree. Spray in the winter months, preferably in January and February, with crude oil emulsion (Formula 18), distillate sprays (Formulas 20 to 23), or miscible oils. The crude oil emulsions are preferable. Thoroughly drench the limbs and trunks. (See Cir. No. 224, Calif. Agr. Exp. Sta., Univ. Calif., Dec, 1920.) Pear Leaf Blister Mite, Eriophyes pyri (Pagen.). — A microscopic mite causing pinkish and yellowish blisters or marks on the young terminal leaves and occasionally reddish blotches on the young fruit. Spray in November or February with lime-sulfur 1-10 to kill hiber- nating mites in buds. Pear Root Aphis, Eriosoma languinosa (Hartig). — A small dark aphid covered with white cottony material and greatly resembling the woolly apple aphis, but attacks only the pear roots. For control see woolly aphis under "Apple." Eliminate young stunted trees and replant healthy ones. The Japanese root is much more resistant to this pest than the French. Pear Thrips, Taeniothrips inconsequens Uzel. — Small, slender, black insect one-sixteenth inch long, appearing before or at the time the blossom buds begin to open and continuing until after blooming- season. The young or white thrips work in the late blossoms, but chiefly on the young fruit and leaves. Spray as often as necessary with the government formula (Formula 24) or dust repeatedly with 5 per cent or 6 per cent nicodust. Watch for adult black thrips as soon as the buds begin to open and apply control measures as soon as any number of the insects appear. (See Cir. No. 223, Calif. Agr. Exp. Sta., Univ. Calif., Nov., 1920.) Red Humped Caterpillar. — See "Prune." San Jose Scale. — See "Apple." Treatment for the Italian pear scale above will also suffice for this insect. Combined Spraying 1. For scale of any kind and for moss and a general clean-up, use a winter spray of lime-sulfur 1-10, crude oil emulsion (Formula 18), or miscible oil. 2. For scab and thrips use Bordeaux mixture (Formula 9), or lime-sulfur 1-10 as cluster buds are opening, adding an extra 10 pounds of lime and 1 pound of 40 per cent nicotine sulfate to each 200 gallons of spray. Oil sprays should not be mixed with lime-sulfur or Bordeaux mixture for this purpose. 34 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 3. For scab and thrips, repeat "2" when first blossoms are about to open. 4. For codling moth and late scab infection, spray when petals are falling with 8 pounds of lead arsenate in 200 gallons of 1-30 lime- sulfur or 200 gallons of Bordeaux mixture. PLUM, PRUNE Armillaria, Wood Decay, Crown Gall, Sour Sap. — See "General Subjects. ' ' Brown Rot. — Not often serious. See "Apricot." Leaf Spot, Coryneum b&ijerinckvi Oud. — See "Apricot," "Peach," and "Almond." Black Scale.— See "Apricot." Brown Apricot Scale. — See "Apricot." Branch and Twig Borer .—See "Apricot." California Peach Borer. — See "Peach." Cankerworms. — See "General Subjects." Cherry Fruit Sawfly. — See "Cherry." Also attacks varieties of plums. Citrus Red Spider, Tetranychus citri McGregor. — See "Two- Spotted Mite" below. Dried Fruit Beetle, Carpophilus hemipterus (Linn.). — A small black beetle less than one-quarter inch long with a reddish spot near the middle of the dorsum. The adults and small yellowish or whitish larvae feed on the dried fruit and continue to breed indefinitely in storage. They may be controlled by fumigation as recommended for grain weevil. See "Grain." Flat-Headed Apple Tree Borer.— See "Apple." Fruit Tree Leaf Roller.— See "Apple." Indian Meal Moth, Plodia inter punctella Hiibn. — The caterpillars are white or pinkish and about one inch long. They feed on the dried fruit, through which they work their way to all parts, leaving behind a trail of excrement, webbing, and spoiled fruit. Their presence is usually first indicated by webbing on the fruit or around the sides of the container. The adults are small, slender, silvery gray moths with the apical ends of the wings coppery. This insect is controlled in the same way as the granary weevil (see "Grain"). Dipping the fruit in scalding water prior to packing kills all forms of this insect. Small packages of dried fruit should be made insect proof to prevent infest- ation in warehouses and storerooms. Circular 227] PLANT DISEASE AND PEST CONTROL 35 Italian Pear Scale. — See "Pear." Mealy Plum Louse, Hyalopterus arundinis (Fabr.). — A pale green aphid covered with a fine white mealy wax ; it collects in great numbers on the under side of the leaves of tender shoots in May and June. Spray with 6 pounds of fish oil soap to 200 gallons of water, or use nicotine soap spray (Formula 27). The soap alone appears to give as satisfactory results as the nicotine soap spray and is much cheaper. Peach Twig Borer. — See "Peach." Pear Thrips.— See "Pear." Red Spider or Almond Mite. — See "Almond." San Jose Scale. — See "Apple." Tent Caterpillars. — See "General Subjects." Two-Spotted Mite, Tetranychus telarins Linn. — This small, pale green or yellow mite, with from two to six dark spots on its back, appears in mid and late summer and does great damage to plum and prune trees by causing the leaves to fall prematurely. Dusting and spraying as recommended for the almond mite (see "Almond") should be done very thoroughly and continued until the first good rains occur in the fall. Tussock Moth.— See "Apple." Combined Spraying For scale, moss, and a general clean-up, spray in winter with crude oil emulsion (Formula 26). POTATO Wilt, Fusarium sp. ; Dry Rot, Fusarium sp. ; Scab, Actinomyces scabies (Thaxt.) G\iss. = Oospor a; Rhizoctonia or Black Scurf, Cor- ticium pagum B. & C. = Rhizoctonia. — Wilt affects plants like a severe drought, causing a premature ripening of the leaves; tubers appear sound, but are mostly infected, as is the soil. Dry rot, associated with wilt in part, is retarded by cool storage. Scab is a soil infection said to be favored by alkaline soil or the application of lime or manure in excess, and retarded by recently plowed under green cover crop. Rhizoctonia appears on tubers as dark scabs, which can be scraped off, leaving the skin unbroken ; under some conditions it causes the dying of young stems under ground. Obtain clean seed from healthy plants. Discard any which show decided dark brown discoloration or decay at stem end to a depth of at least one-quarter inch from the end. Soak the seed before cutting for one and one-half hours in a solution of 36 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 1-1000 corrosive sublimate (1 ounce to 8 gallons of water), or for 2 hours in formaldehyde, 1 pound to 30 gallons of water. Use a wooden vessel for the sublimate and have the tubers as clean as possible. Jelly End, Soft Rot. — Infection in wounds with several fungi, Pythium, Rhizopus, etc. Avoid injury and bruising in digging. Potato Late Blight, Late Rot, Pkytophthora infestans (Mont.) De Bary. — Translucent spots appear on the leaves and stems, which spread rapidly till entire top is wilted and prostrate. The tubers show sunken spots at digging and rot in storage. Spray with Bordeaux mixture (Formula 9) immediately after rains. Aphids (Various Species). — Dust thoroughly with 5 per cent nico- dust or spray with 1 part of 40 per cent nicotine sulfate to 800 parts of water. Armyworms and Cutworms. — See "General Subjects." Flea Beetles and Leaf Beetles. — See "Melon." Use Bordeaux mixture (Formula 9) as a repellent, or a nicodust lead arsenate mixture. Garden Nematode or Eelworm. — This animal produces a pimply or warty surface on the potato and small brown dots just beneath the skin. Plant only clean seed and avoid infested soil. Grasshoppers. — See "General Subjects." Potato Stalk Borer, Trichobaris trinotata Say. — The larvae are small, pale yellow or white, and not over one-half inch long ; they bore throughout the middle of the stalks, causing them to wilt and die. The adults hibernate in the old dry stalks, which should be raked up after digging and burned. This affords an almost perfect control if thoroughly done. Potato Tuber Moth, Phthorimaea operculella (Zeller). — The full- grown caterpillars are white or pinkish and not over three-quarters inch long. They make numerous burrows just under the skin and throughout the tubers, continuing to work as long as the tubers are available. Infestation may occur in the field or in storage. Hill up well around the growing plants and remove the potatoes as soon as dug to prevent infestation in the field. Store in a clean, uninfested place. If infested, fumigate with 20 to 30 pounds of carbon bisulfide to every 1000 cubic feet of air space at a temperature 70° F. or over. Plant only clean seed. Tomato and Tobacco Worms. — See "Tomato." Wireworms. — See "General Subjects." Circular 227] PLANT DISEASE AND PEST CONTROL 37 Combined Spraying Bordeaux mixture will control not only the flea beetles but will materially aid in subduing many fungus diseases. PUMPKIN. See "Melon" ROSE Mildew, Sphaerotheca pannosa (Wallr.) Lev. and 8. humuli (D. C.) Burr. = Oidium. — White powdery mildew spreads over young stems or leaves, causing distortion or dropping of leaves and discoloration ; severe in cool coast districts. Spray with lime-sulfur 1-10 before the spring growth starts. Use dry sulfur, sulfur paste, or lime-sulfur 1-35 when disease first appears. Aphids (Various Species). — Two common aphids usually infest roses: the large green and pink Macrosiphum rosae (Linn.), which commonly attacks the tender tips and buds, and the small green Myzaphis rosarum (Walk.), which works on all parts of the plant and produces large quantities of honey dew, resulting in the smutting of the plants. Both may be effectually controlled by dusting liberally with 5 per cent nicodust, by spraying with nicotine sulfate, 40 per cent, one part to 1000 parts of water, or by thoroughly hosing off the plants every two or three days with a strong water pressure and a coarse nozzle. Fuller's Rose Beetle.— See "Citrus Fruits." Raspberry Horntail. — See "Bush Fruits." Rose Scale. — See "Bush Fruits." Spray infested portions of the plants during the winter months with miscible oils. Rose Snout Beetle, Rhynchites bicolor Fabr. — A small red and black snout beetle, scarcely one-quarter inch long, which punctures the buds of roses, causing numerous holes in the petals when the flowers open. Jar beetles in pan of oil in the early mornings. A 10 per cent nicodust has given good control in some places. Combined Spraying For fungus diseases and aphids, a 40 per cent nicotine sulfate may be added to sulfur sprays as given above, and a sulfur nicodust may also be used for mildew and aphis. 38 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION SNAPDRAGON Rust, Puccinia antirrhini D. & H. — Brown rust sori break out through the leaf and stem. Infection is usually heavy and the plant becomes unsightly and dies. Water and fertilize freely to stimulate growth. Destroy badly affected plants and clean up thoroughly in the fall. Pentstemon is a fairly good substitute for snapdragon, and does not rust. Aphids. — Dust thoroughly with 5 per cent nicodust. SORGHUM, SUDAN GRASS, AND BROOM CORN Head Smut, Sphacelotheca reiliana (Kiihn.) Clint. — Whole head or panicle becomes a black mass. Method of treatment not yet devel- oped. Affected plants should be destroyed at first appearance. Affects also corn. Kernel Smut, Sphacelotheca sorghi. — Kernels form enlarged grains which become fragile and filled with a black powder. Controlled by seed treatment. See "Grain." Aphids (Various Species). — See "Grain." Armyworms and Cutworms. — See "General Subjects." Granary and Rice Weevils. — See ' ' Grain. ' ' Grasshoppers. — See "General Subjects." SPINACH Armyworms and Cutworms. — See "General Subjects." Poisoned bran mash sown broadcast over the fields has proved very successful in completely protecting young plants. Beet or Spinach Leaf Miner, Chortophila hyoscyami Panzer. — Small white maggots mining the leaves and causing discolored areas. Keep down all weeds about the fields, burn refuse tops, harvest as early as possible. Winter grown spinach usually escapes the attacks of this insect. Flea Beetles.— See "Melon." Grasshoppers. — See "General Subjects." Melon Aphis.— See "Melon." SQUASH. See Melon Circular 227] PLANT DISEASE AND PEST CONTROL 39 STRAWBERRY Leaf Spot, Mycosphaerella fragariae (Tul.) Linn. = Ram ularia. — Dead spots on leaves, one-quarter inch or less in diameter with red borders ; if abundant it lowers the vitality of the plants. Clean up and burn the leaves in late fall. Spray with Bordeaux mixture (Formula 9) if the disease becomes serious. Leaf and Stem Rot. — Symptoms are those of acute drought injury ; plants die back in hot weather and inferior growth comes up later with poor production ; roots are killed off, apparently by poor soil conditions. Use less water. Improve drainage. Wash out alkali in winter by flooding. Gray Mold, Botrytis rot. — See "Bush Fruits." Strawberry Aphis, Myzus fragaefolii Ckll. — A very small pale yellow aphis occurring in great numbers on the under sides of the leaves, and often smutting the foliage. Defoliate the plants in winter. Dust liberally with 5 per cent nicodust as soon as the aphids appear, applying it to the under side of the leaves with an upturned discharge pipe. Strawberry Crown Moth, Aegeria rutilans H. Edw. — A.white cater- pillar one-half inch long or less boring in to the crown of the plant, causing it to turn yellow and die. Remove and burn infested plants as soon as discovered. Be sure of clean nursery stock. Strawberry Flea Beetle, Haltica ignita Illiger. — A bright metallic, golden, green, or purplish flea beetle, one-sixth inch long, feeding upon the leaves of the plants. Use Bordeaux mixture (Formula 9) as a repellent. Strawberry Leaf Beetle, Typophorus canellus (Fabr.). — A small brown beetle with black markings on the dorsum and averaging one- eighth inch long. The adults eat numerous small irregular holes in the leaves, while the small white larvae attack the roots. It is a severe pest, and should be eradicated, if possible, by destroying all infested vines and thoroughly sterilizing the soil by steam or carbon bisulfid. Established infestations may be reduced by thoroughly spraying with arsenate of lead (Formula 2), or by dusting with 1 part of basic powdered arsenate of lead to 4 parts of powdered hydrated lime. Strawberry Root Weevil. — The one known infestation of Oiio- rhynchiis rugifroms Gyll. in California is quarantined. Secure plants from uninfested district. Report any suspicious cases to the State Department of Agriculture, Sacramento, Calif. 40 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Two-Spotted Mite, Tetranychus telarius Linn. — See "Bean" and "Prune." Though ordinarily controlled with dry sulfur, this method cannot be used on strawberries because of the severe burning to the foliage. Very small amounts of sulfur in the ditches between the rows have afforded some relief. SWEET POTATO Soft Rot, Rhizopus nigricans Ehr. — Mainly a storage trouble ; rot starts at injuries and progresses rapidly ; decayed part becomes cov- ered with white mold which later turns black. Avoid bruising. Dry well before storing. For long keeping, pack in dry sand. Moisture and temperature requirements of sweet potatoes in storage are different from those of most other products and must be carefully observed. Wilt, Fusarium sp., Black Rot, Ceratocystis fimbriata (E. & II.) Sacc. — Wilt affects growing plants in the field. Black Rot forms dark patches of dry rot which begin development in the field and continue in storage. Infected potatoes are bitter. Get clean seed potatoes from an uninfected locality. Destroy diseased vines after digging. TOBACCO. See "Tomato" TOMATO. See also < ' Potato ' ' Blossom End Rot. — Dry spot appears at blossom end of green fruit and develops slowly. Avoid drought or irregular irrigation. Damping-off. — See "General Subjects." Late Blight, Late Rot, Phytophthora infestans (Mont.) De B. — In late moist weather large vague spots appear on the leaves, at first dark and watery, becoming slightly frosted with emerging fungus threads below, then deteriorating rapidly. Similar spots appear on the fruit, not well marked at first, but the fruit spoils rapidly. Spray with Bordeaux mixture (Formula 9) immediately after rains. Wilt, Summer Blight. — Plants become pale, leaves roll upward, exposing purplish veins, plants become worthless and most of them die. Use plants free from damping-off. Replant if not too late. Cannot be controlled in some years. Armyworms and Cutworms. — See "General Subjects." Grasshoppers. — See "General Subjects." Darkling Ground Beetles, Blapstinus sp. and Eurymetopon hicolor Horn. — Small, dull black or bluish-black beetles, scarcely more than one-quarter inch long, living in the soil and responsible for much dam- Circular 227] PLANT DISEASE AND PEST CONTROL 41 age to young plants shortly after transplanting. Before resetting, wrap the stems of the young plants from roots to tops with tissue paper so as to have three or four thicknesses for protection, or scatter poison bran mash (Formula 4) over the ground at planting time. Flea Beetles. — Dust with powdered arsenate of lead, 1 part to 4 parts of dry lime or sulfur, nicodust and arsenate of lead, or spray with Bordeaux mixture (Formula 9). Garden Nematode. — See "General Subjects." Tomato Worm, Protoparce sexta Joh. and Tobacco Worm, P. quin- quemaculata Haw. — Large green worms often attaining a length of four inches. They strip the leaves from the vines. The adults are known as humming bird moths because of their large size and swift flight. They are gray with yellow spots on the sides of the body and have a wing expanse of 4 or 5 inches. The caterpillars may be con- trolled by hand picking, i.e., cutting the worms in two with a pair of scissors, or by dusting the vines with 1 part of powdered arsenate of lead to 4 parts of finely ground hydrated lime. WALNUT Blight, Pseudomonas juglandis Pierce. — Young tender parts are attacked. Spots at first watery, soon turning black, often spread and kill young nuts, leaves, or tender tips of shoots. No specific remedy. Give the trees the best possible care. Thin out the tops of the old trees. Control aphis. Plant resistant varieties. Crown Gall, Wood Decay, Armillaria. — See "General Subjects." Melaxuma, Dothiorella gregaria Sacc. — Black sunken cankers de- velop on larger limbs and trunks; the limb may be girdled and the part above die. Cut out diseased bark areas and apply Bordeaux paste. Winter Killing. — Irrigate about November 1, if no good rains have fallen. Whitewash trunks in the fall. Do not irrigate after August, except as above. Codling Moth, Cydia pomonella (Linn.). — See "Apple." This worm feeds on the green husks or usually bores directly into the kernel of the walnuts before they are mature, and also often works its way into the kernel after the shell becomes hardened by making an entrance in the suture at the base. It may be controlled by spraying with basic arsenic of lead or by dusting with powdered basic arsenate of lead and hydrated lime when work on husks of nuts is first observed in the spring — May, June, or July — depending upon climatic conditions due to location near the coast or inland. Consult local horticultural officials. 42 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Frosted Scale, Lecanium pruinosum Coq., and Cherry or Calico Scale, L. cerasorum Ckll. — Same control as for brown apricot scale. See "Apricot." Indian Meal Moth. — Attacks walnuts in storage. See "Prune." Nautical Borer, Xylotrechus nauticus Mann. — The borers are small, fleshy, white or yellowish grubs, with slightly enlarged anterior end, and about three-quarters inch long. The adult beetles are one-half inch long, dark with narrow broken yellow or whitish cross bands on the elytra. The larvae work in the small twigs, limbs, and trunks of both healthy and sickly trees. Cut out and burn all infested portions. Destroy all dead oaks or prunings in the neighborhood to eliminate breeding places. Red Humped Caterpillar. — See "Prune." Two-Spotted Mite. — See "Prune." Dust thoroughly with dry sulfur. Walnut Aphis, Chromaphis juglandicola (Kalt.). — A small pale yellow aphis occurring in great numbers on the under sides of the leaves and producing great quantities of honey dew, which causes severe smutting of the foliage. Dust thoroughly with a 2 per cent nicodust during last week of May or the first part of June. Sometimes a second application is necessary in July or August. Walnut Blister Mite, Eriophyes erinea Nalepa. — A microscopic mite producing yellow or brown felt-like galls on the under sides of the leaves. It is not a serious pest, but may be cleaned up by spraying trees with lime-sulfur 1-10 in the spring when the buds are swelling. Control measures are not recommended except in extreme cases. Yellow-Necked Caterpillar, Dot ana ministra Drury. — A black, hairy caterpillar with numerous longitudinal yellow stripes on the back and sides and a yellow or orange-colored neck. It averages about two inches in length and is closely related and similar in habits to the red humped caterpillar, and may be handled in the same way. See same under "Prune." WATERMELON. See "Melon" WHEAT. See "Grain" Circular 227] PLANT DISEASE AND PEST CONTROL 43 GENERAL SUBJECTS ANTS Ants are not only serious household pests but do harm in the garden and orchard by distributing plant lice, scale insects, and other honey- dew producing insects, and protecting them from parasitic enemies, which would otherwise destroy great numbers of these pests. The ordinary small house ants, which give off a pungent character- istic "ant" odor when crushed, are best controlled by using various strong, arsenic, and syrup poisons sold as ' ' ant poisons. ' ' The Argen- tine ant, which gives off no characteristic odor, is controlled by a very weak arsenic and syrup poison which is carried to the young by the workers and which gradually kills out the whole colony. For this pest use Formula 7 or 8, or buy special Argentine ant poison. Home-made containers for the latter poison may be made by punch- ing small holes around the tight-fitting tops of cans and then dipping in hot paraffine to prevent rusting. A sponge is placed in the bottom and thoroughly wet with the poison, the lid is securely fastened, the container marked ' ' Poison, ' ' and then hung up under or in the house, or in the gardens or orchards, away from the reach of children. Small fruit jars with holes punched in the lids may be used instead of cans, and if screwed very tightly are less likely to be opened by children. ARMILLARIA ROOT ROT (OAK FUNGUS), Armillaria mellea (Vahl.) Quel. Caused by a native fungus which lives saprophytically and para- sitically in roots of woody plants. Trees and bushes are killed in spots, which enlarge year after year. Affected trees fail gradually from dis- eased side or die suddenly in summer. Under the affected bark of roots there is a yellowish white fan-shaped mycelium which progresses into live bark. Black shining root-like strings (rhizomorphs) grow out from old rotting roots. The wood decays with a uniform white rot. Large tan-brown toadstools (edible when cooked) arise from old infections, October to February. Surgery as in Crown Gall or Pear Blight can sometimes be practiced on roots and crowns of trees not too far gone. Black walnut, French pear, and fig roots are practically immune. Annual fibrous rooted plants are rarely injured. Affected areas in orchard may be isolated by opening a trench 3 to 4 feet deep 44 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION around them. This may be filled immediately if reopened every two years to keep the roots cut off. Nursery should not be planted in in- fected soil. ARMYWORMS AND CUTWORMS General Life History. — The adult members of this family (Noc- tuidae) are practically all night-flyers. The caterpillars of many are known as armyworms and cutworms and are among the most destruc- tive of insect pests. They often advance from field to field in great numbers, like an army, devastating as they go. Like the grasshoppers, they attack practically all kinds of plants, including field and truck crops, vineyards and orchards, as well as flowers and weeds. The adults lay their eggs in spring and the larvae become exceed- ingly numerous in early summer, when most of the damage is done. The pupal stage is passed under ground, the light or dark-brown naked chrysalids being housed in small earthen cells. There are several broods a year. The winter is usually spent in the pupal stage, but some larvae as well as adults hibernate. A hibernating larva often seriously injures grapevines in the spring by eating the buds. Control. — The control of these insects has been a difficult problem for years, and even today the methods worked out do not always give relief. Clean culture in fall and thorough plowing of infested fields to kill the hibernating pupae in the cells is supposed to greatly reduce the next year 's broods. This has been recommended as especially im- portant in pea fields and gardens. "When the worms begin to march trenches may be plowed across and ahead of their paths with a perpendicular wall in front of the advance. The worms, not being able to cross, will gather in great masses in these trenches and can be easily killed by spraying with crude oil or by crushing them with a narrow disk or roller. Arsenical sprays applied as soon as the larvae begin to appear will sometimes materially aid in protecting crops like potatoes, tomatoes, young trees, grapevines, etc., but are seldom practical for forage crops. Poisoned baits (Formulas 4 and 5) sown in the infested fields will kill countless worms, and these afford by far the most satisfactory means of killing these insects under all conditions. In fields, pastures, orchards, and gardens, the poisoned baits may be freely sown over the plants. The armyworms and cutworms will eat the bait in preference to growing vegetation. Light traps are also used to capture the adults, but these have never seemed to greatly lessen the attacks, because large numbers of the moths captured have previously laid their eggs. Circular 227] PLANT DISEASE AND PEST CONTROL 45 Natural Enemies. — By far the most important factors in the con- trol of armyworms and cutworms are natural enemies. The parasitic tachinid flies kill countless numbers of them. Hymenopterous para- sites of the family Ichneumonidae also prey upon the young. The predaceous ground beetles of the family Carabidae devour the worms and destroy great numbers. That armyworms and cutworms are not injurious every year is undoubtedly due to the work of these natural enemies. CANKERWORMS Small green or dark measuring worms less than an inch long, which feed upon the leaves and young fruit and drop down on a silken thread when the tree is jarred. The females are wingless and crawl up the trees in the fall or spring to lay their eggs on the limbs and small branches. Egg-laying on the trees is prevented by placing tanglefoot, cotton, or permanent wire screen bands around the trunks of the trees in the fall in order to catch both the fall and spring forms. The cater- pillars are easily jarred from the trees, but will crawl up again if not obstructed. Spraying with arsenate of lead (Formula 4) will also give CROWN GALL, Bacterium tumefaciens S. & T. Rounded fleshy to woody tumors form on roots or sometimes on above-ground parts, usually starting from wounds, persisting and growing at the edges from year to year, often girdling or causing the tree to break off. For nurseries, avoid old vineyard, orchard, or berry land which has been seriously infected. Throw out all affected nursery trees. The clean trees in a lot having a large percentage affected are of doubtful value. In orchards, occasionally examine crown and main roots, especially of stunted trees. When not too far advanced this disease may be controlled by chiseling out the galls, removing all ab- normal tissue to healthy bark and down to sound wood, sterilizing with corrosive sublimate (Formula 28 or 28a), and covering the wounds with Bordeaux paste or asphaltum. The trees must be gone over again after vigorous growth has been going on for several weeks and the new galls which arise at the wound margins treated. Reinspection is essen- tial. Badly affected and stunted trees should be pulled out and re- planted, using fresh soil. DAMPING-OFF Young seedlings rot at or below the surface of the ground and fall over or wilt. Many may die before emerging. Cause, various soil fungi, Pythium, Rhizoctonia, Fusarium, and others. Best controlled 46 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION by skill in watering. Water the plant beds only in the morning and on bright days. Do not sprinkle oftener than necessary. In green- houses or frames give plenty of ventilation. In making citrus seed beds put an inch or two of dry sand on the top of the soil. Some forms of Damping-off can be prevented by steam-sterilizing the soil before planting, or by drenching with a solution of 4 pounds of formaldehyde in 50 gallons of water, using 1 gallon of solution to every square foot. This must be done two weeks in advance so that no odor of formalde- hyde remains at planting time. Where damping-off has started, spraying the plants and ground with Bordeaux may do some good. FLIES Should be prevented from breeding by keeping manure, garbage, and similar refuse material covered tightly. For poisoning flies in the house, use about 2 per cent formaldehyde solution exposed in saucers, adding a little sugar. FROST AND COLD INJURY With young citrus trees in frosty localities, wrap the trunks with corn or milo stalks in winter. Heap up earth around the butts. En- close tender valuable young trees with burlap covers. For bearing groves obtain detailed information about methods and appliances for smudging with oil fuel. (See also Sour Sap.) Many plants are injured and disfigured by cold at critical stages of development, even when it is not cold enough to kill or even noticeably injure them at the time. GRASSHOPPERS Scatter poison bran mash or citrus bran mash freely (Formula 4 or 5). Be sure to mix the bran and poison thoroughly. Scatter in alfalfa fields about 4 o'clock in the afternoon and around orchard trees or other plants early in the morning. GUMMOSIS Gum formation in itself is not due to any one specific disease, but may be brought about by many different causes. In stone fruit and citrus trees gumming is simply a symptom of distress, which may be due to specific infections or various other causes, such as unsuitable soil, poor condition of soil, sunscald, excess or lack of water, frost, or attacks of parasites. Treatment must vary according to cause. Badly gummed branches may be removed, gummy diseased areas of bark cut out, and the wounds treated as in citrus gummosis. Splitting the bark is useless and often harmful. Circular 227] plant disease and pest control 47 NEMATODE (EEL WORM) Microscopic worms of several species penetrate the tender tissues of plants. The garden nematode causes rounded irregular fleshy swell- ings or root knots on tender roots. If abundant, the roots may become much distorted and swollen, growth stops, and early rotting off follows. Do not attempt to grow susceptible crops on infested soil. Keep such areas clean cultivated in summer or in a cereal crop. Grain may be grown in winter. Almost all important crops, except cereals and some fruit trees, are attacked by the garden nematode. The beet nematode attacks some other plants, and where it occurs careful rota- tions should be followed with total exclusion of beets for many years. Alfalfa is not seriously affected by the common species, but carries it over to future crops. Alfalfa may be safely planted on beet nematode soil. Nematodes are worse on sandy soils. PHYSIOLOGICAL DISEASES (Little Leaf, Exanthema, Die-Back, Mottled Leaf, Rosette, Bitter Pit, Dry Rot, Blossom-End Rot) Diseases of a specific nature of which the cause is not known and of which the symptoms seem unlike the usual effects of unfavorable conditions or parasites. Most of these troubles show a relation to soil conditions and occur especially in dry, sandy, gravelly, or hardpan soils, those very deficient in humus, or under conditions of irregular soil moisture. Trees standing over old barnyards or corrals or where excessive amounts of manure have been applied are also likely to show some of these troubles. The most promising methods of treatment are increasing the humus content of the soil by means of green manure crops and mulches, breaking up all hardpan and plow-soles, more care- ful irrigation to insure the maintenance of a proper and uniform moisture condition of the soil down to a depth of several feet and throughout the season until rains occur, and planting alfalfa in orch- ards where plenty of water is available. The soil in areas where these troubles occur should be examined for alkali or other injurious sub- stances. Where any of these diseases are serious and persistent it may be better to grow some other crop than to keep on with one which is seriously affected. RABBITS If very abundant, must be fenced out of young orchards and gar- dens to avoid serious damage. Shooting and poisoning are the prin- 48 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION cipal means of destruction. An application of whitewash containing bitter aloes to the trunks of young trees is sometimes recommended, but this has not shown much value in actual practice. Soaked, chopped alfalfa sprinkled with strychnine, Paris green or white arsenic is very effective in destroying cotton-tails. SLUGS AND SNAILS May be controlled to some extent by thoroughly dusting finely powdered hydrated lime over the infested plants, but recent investi- gations have shown that a 5 per cent nicodust is very effective in killing these pests if applied late in the evening or on dull days when the animals are at work on the plants. Trapping by means of boards or wet sacks and killing those taking shelter thereunder is effective in a small way. SOUR SAP, WINTER INJURY. Also see "Sunburn" All the ordinary forms of sour sap are due to extreme variations in temperature. Differences in the effect upon individual trees or orch- ards are due to differences in condition and susceptibility of the trees, produced mostly by variation in the moisture condition of the soil. Do not force growth late in summer. Irrigate, if possible, about No- vember 1, if no heavy rain has fallen. Whitewash bodies of trees early in November. Sour sap seems to be associated with hardpan or periods of surplus water in the soil. Good drainage should be emphasized. A furrow may be opened in early winter on either side of the tree row to carry off surplus winter rains and prevent the soil from remaining saturated for prolonged winter periods. Numerous instances have been observed where open irrigation ditches have drained adjacent tree rows during the winter. Trees in the drained soil have escaped sour sap while those farther from the ditch in soil saturated with winter water have suffered badly. SQUIRRELS AND GOPHERS May be controlled by persistent poisoning, fumigation with carbon bisulfide, trapping and shooting. For poisoning material, the commer- cial preparations may be used or Formula 33. Poisoned Fruit. — Strychnine sulfate may be sprinkled over orange halves or watermelon rind, or a solution of 1 ounce of strychnine sulfate dissolved in 1 gallon of boiling water may be used for saturating grain or other material, after allowing the solution to cool. Circular 227] PLANT DISEASE AND PEST CONTROL 49 SUNBURN Whitewash bodies in fall as well as spring. Shape the trees so that their trunks are shaded. Cut young trees back well before planting. Shade trunks with shakes or protectors. Do not allow trees to suffer from drought. Tests show that the coloring matter in the bark of the trunk and exposed main limbs absorbs heat enough on sunny days in winter to raise the temperature of the growing layer 35° to 40° F. above the temperature of the air. As soon as the sun goes down the tree cools rapidly to atmospheric temperature, which may be freezing or below. Whitewash reflects the heat, so that the growing layer does not get warmer than the air, the cells remain dormant during the day, and are not injured by low temperatures at night. The above also applies in opposing sour sap. TENT CATERPILLARS Gray or brown, hairy caterpillars with row of white spots on back or pale bluish lines on sides, measuring from 1 to 3 inches long. They either live in compact colonies or in tightly woven webs or tents which are conspicuous on the trees. Entire colonies may be exterminated by cutting off or burning with a torch. Those on the trunks and large limbs may be killed by spraying with kerosene or concentrated oil emulsions. The small dark egg masses encircling the smaller limbs may be pruned out when the trees are dormant and burned. Spraying with arsenate of lead (Formula 1 or 2) will control the caterpillars effectually. TREE WOUNDS, PRUNING CUTS Make a clean, smooth cut, trimming the bark down smoothly to sound tissues around the edges. In the case of branches, make a smooth cut, leaving no projecting stub. Thoroughly cover the wound with Bordeaux paste (Formula 10), and after callus starts to form about the edges cover with grade D asphaltum put on in a melted condition. Go over the work occasionally, especially in summer or early fall, and renew the application of asphaltum until the wound is entirely healed. Bordeaux mixture retards the formation of callus and the edges of the wound may be covered with asphalt first to protect the cambium and the Bordeaux applied later. Some prefer to paint the whole wound at once with hot asphaltum. Others prefer to use the asphalt paint cold, but this should be done with care to keep cracks in the wood thoroughly covered. Paints like white lead and oil, which harden and may crack, can not be recommended. 50 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION WIREWORMS Wireworms get their name from their smooth, round bodies, which are usually shiny, varying in color from pale yellow to dark brown. The common injurious forms are about one inch long. They live in the soil, preferring sandy loams rather than heavy soils, although they may be found in either. The larval stages last from 1 to 3 years> so that to be effective control measures must cover the maximum period. The adult beetles are known as "click beetles " because of their ability to jump in the air with a clicking sound. They are mostly inconspic- uous beetles of various shades of brown or entirely black, about one- half inch long. They are active and fly freely. Control measures are difficult because of the underground habits of the larvae, and as yet have not been satisfactorily worked out for the different species. Clean culture and crop rotations are the most reliable practices, while much good comes from thorough cultivation. Trapping the adults with small piles of straw and burning them in fall and winter destroys large numbers. Replanting is often necessary with many crops such as potatoes, beans, peas, melons, etc. Some con- trol is claimed from scattering poison bran mash (Formula 4) over the surface of the ground. FORMULAS AND DESCRIPTION OF MATERIALS ARSENICALS Acid Lead Arsenate (Lead Hydrogen Arsenate, Di-lea(i Arsenate, Often Labeled "Standard" or Lead Arsenate). — The acid type of lead arsenate contains more poison per pound than the basic type, is a stronger poison and acts more quickly. It is, however, somewhat sus- ceptible to the action of other chemicals, particularly those of an alka- line nature (such as soaps, lime-sulfur solution, etc.), and is more or less dissolved by them when used as a combination spray. In moist climates along the coast, or in continuous damp, cloudy weather else- where, whether used alone or in combination with other sprays, some of the arsenic is apt to be dissolved and to cause serious foliage injury. It is not considered a safe arsenical for use on stone fruits, beans, or other susceptible plants. Basic Lead Arsenate (Usually Labeled ' ' Tri-plumbic ' ' or ' 'Neu- tral"). — The basic type of lead arsenate is a weaker poison and acts more slowly. It is not decomposed, however, by chemicals of an alka- line nature, such as are usually applied with it as a combination spray, Circular 227] PLANT DISEASE AND PEST CONTROL 51 nor by the damp weather of the coast regions. It is considered the only safe arsenical to use on stone fruits, beans, or other susceptible plants. The lead arsenates are usually sold as a paste containing about 50 per cent of water, or as a dry powder. The paste should be thinned somewhat with water and worked into a smooth cream before adding to the spray tank. The powder may be added directly to the tank and mixed by means of the agitator. For codling moth and most defoliating insects use : Formula 1 Dry acid lead arsenate (paste, 4 to 8 pounds) 2 to 4 pounds Water - 100 gallons Or Formula 2 Dry basic lead arsenate (paste, 5 to 10 pounds) 2% to 5 pounds Water 100 gallons Dry or powdered lead arsenate contains twice as much arsenic as the paste, therefore use only one-half as much of it. Zinc Arsenite is a stronger and more active poison than either type of lead arsenate, and is useful in controlling the various caterpillars which are troublesome on pears and apples in the early spring, but is very apt to cause injury if the application is made after the time of full bloom. Formula 3 Zinc arsenite powder 3 pounds Water 100 gallons White arsenic (Arsenic trioxide) is only sparingly soluble in water, although sufficiently so to prohibit its use on plants as an insecticide. Its use as a stomach poison is therefore limited to the preparation of poison baits for the control of grasshoppers, armyworms, cutworms, etc., and in some other cases where the insecticide is not to be applied to growing plants. Poison Bran Mash. Formula 4 Bran 25 pounds White arsenic 1 pound Molasses (cheap blackstrap preferred) 2 quarts Mix the arsenic and the bran dry and add the molasses which has been diluted with water. Add enough water and mix thoroughly to make a dry mash which will broadcast easily. 52 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Citrus Bran Mash. Formula 5 White arsenic .. - 1 pound Molasses (cheap blackstrap preferred) 2 quarts Lemons (or oranges) - 6 fruits Water (about) 4 gallons Bran 25 pounds Mix the above materials as follows: Stir thoroughly the white arsenic, molasses, and water first. Grind the lemons, including the rinds, in a meat grinder, or chop fine, and add to this liquid. Then slowly pour this over the bran and stir thoroughly until an even mix- ture is secured. The amount of water to use in the preparation of these baits will vary according to the coarseness of the bran, or substitutes. A barely moist mash is preferable to a wet one because it does not harden under the heat of the sun and remains palatable, while wet mash becomes baked and unattractive. Substitutes in Poison Baits. — Paris green may be substituted for white arsenic in Formulas 4 and 5. Alfalfa meal, shorts, or rice meal have been successfully used as a substitute for bran in the preparation of the above formulas. Sodium Arsenite. — This arsenical is readily soluble in water and is one of the most violent of the plant poisons. It probably acts more quickly than any of the better known arsenical poisons, and is com- monly used in the preparation of weed killers, poison fly-papers, cattle dips for the control of ticks, ant syrups, and to some extent in the preparation of poison baits. Sodium arsenite may be purchased ready made as a white powder, but it is not always readily obtained at pharmacies, nor can it always be depended upon to contain a uniform amount of arsenic. This chemical can be easily prepared from white arsenic by combining the latter in the presence of water with sal soda, soda ash, caustic soda, or a good grade of concentrated lye in the following proportions : Sal soda or washing soda, 2 parts to 1 part of white arsenic. Soda ash, 1 part to 1 part of white arsenic. Caustic soda, 1 part to 2 parts of white arsenic. Concentrated lye, 1 part to 2 parts of white arsenic. If sal soda or soda ash is used it is necessary to boil the mixture fifteen or twenty minutes before the arsenic is dissolved. If caustic soda or concentrated lye is used, little or no heat is necessary. In either case, a corrosive chemical is formed known as sodium arsenite. Circular 227] PLANT DISEASE AND PEST CONTROL 53 A soluble arsenical can be made by using one part of caustic soda to four parts of arsenic trioxide. Such a solution, however, has a tendency to form crystals on standing. Sodium Arsenite. Formula 6 Sal soda 2 ounces (or 2 pounds) White arsenic 1 ounce (or 1 pound) Water (about) y 2 pint (or 1 gallon) Put all the ingredients together in an iron or graniteware kettle (do not use aluminum) of sufficient size to allow for considerable frothing, and boil fifteen or twenty minutes, or until the solution is clear. A modification of Professor C. W. Woodworth's formula which has been successfully used in municipal compaigns against the Argen- tine ant is as follows : Ant Syrups. Formula 7 Strong for Weak for Argentine ants native ants Large quantity Small quantity White arsenic 2 oz. 1 oz. 1 scruple Caustic soda 2 oz. 1 oz. y> teaspoonful Sugar 1 lb. 20 lbs. 1 lb. Water 1 pt. 3 gals. 1 pt. For native ants, expose a small quantity of the strong poison. For the Argentine ant, place a sponge in a fruit jar, saturate it with the weak poison, make a few nailholes in the cover and keep jar in pantry and several others in the yard about the house. Add more poison from time to time. The U. S. Bureau of Entomology recommends a later formula for the preparation of Argentine ant syrup which is said to be superior to any other formula tested by them, "on account of its stability at high temperatures, freedom from crystalization, and continued attrac- tiveness." Government Argentine Ant Syrup. Formula 8 Granulated sugar 9 pounds Water 9 pints Tartaric acid (crystallized) 6 grams Benzoate of soda 8.4 grams Boil slowly for 30 minutes. Allow to cool. Dissolve sodium arsenite (C. P.) 15 grams In hot water y 2 pint Cool. Add poison solution to syrup and stir well. Add to the poisoned syrup : Honey ..,„.„.„ ..„„, 1% pounds Mix thoroughly. 54 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION COPPER COMPOUNDS Bordeaux Mixture (Average Strength). Formula 9 Bluestone 16 pounds Quicklime • 20 pounds Water 200 gallons Dissolve the bluestone and slake the lime in separate vats, the blue- stone to be kept from contact with all metals except copper. Thor- oughly mix the dissolved bluestone with one-half the water and the slaked lime with the other half. Run the two mixtures together in a single stream into the spray tank through a fine screen. For conven- ience, the mixing vats may be placed on an elevated platform, and the two parts mixed as they are flowing into the spray tank. The milk of lime should be continuously stirred during the mixing. A somewhat less satisfactory Bordeaux mixture may be made as follows: Slake the lime and dissolve the bluestone in separate barrels as above. Fill the spray tank half full of water, add the dissolved bluestone ; strain in the slaked lime while the agitator is running ; add remainder of water, and mix thoroughly. Bordeaux Paste. Formula 10 A. Bluestone 12 pounds Water 8 gallons B. Quicklime 24 pounds Water 8 gallons Dissolve the bluestone and slake the lime separately in the amounts of water specified. Then mix together equal quantities of each ingred- ient, making up only enough for each day 's use. Commercial Bordeaux Mixture. — Several preparations of this sort are on the market in the form of a paste or dry powder to be diluted with water. Objection is sometimes made to these preparations that they will not remain in suspension in water as well as the home-made Bordeaux mixture, but some of them are probably as good or better than the average mixture prepared on the ranch. The commercial preparations are more expensive, but also more convenient for use, and are of especial value to the small grower. Circular 227] PLANT DISEASE AND PEST CONTROL 55 Resin-Bordeaux Mixture. Formula 10a Bluestone 20 pounds Lime : 26 pounds Resin 10 pounds Soap (soft) 16 pounds Water 200 gallons Melt the resin in an iron pot, then add the soft soap, heat and stir until well mixed and quite soft. Add hot water and boil and stir for some time until thoroughly dissolved. Add this to the Bordeaux which has been made in the usual way. (From Univ. Calif. Exp. Sta. Bull. 165, p. 77.) This is for use on plants with very smooth waxy surfaces on which fungicides do not spread and adhere well. Bluestone (Copper Sulfate). — A soluble compound of copper, the raw material for the preparation of most other compounds of copper. This cannot be used on foliage. For dipping grain use : Formula 11 Bluestone ~ 1 pound Water 5 gallons Dip for 3 minutes. Followed by : Quicklime 1 pound Slaked in water 10 gallons For lemon wash water use : Formula 12 Bluestone 1% pounds Water 1000 gallons SULFUR AND SULFUR COMPOUNDS Dry Sulfur. — For dusting upon plants for the control of surface mildew, red spider, or other parasites the fineness of the sulfur is an all-important consideration. Flowers of sulfur, the finest and fluffiest grade of sublimed sulfur, has been heretofore recommended for appli- cation as a dust, but at present there are upon the market several brands of extremely finely ground sulfurs, which are as fine as some of the best grades of sublimed sulfur and no more expensive. Some of these sulfurs, which have been specially prepared for dusting, are ground to pass a 200-mesh bolting cloth. These are apt to cake and to clog the dusting apparatus. If three parts of sulfur are thoroughly mixed with one part of hydrated lime, kaolin, or other inert powder, these difficulties may be avoided. 56 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Sulfur Pastes or Wettable Sulfurs. — For various reasons it is often desirable to mix sulfur and water and apply to plants as a spray. Sulfur, however, is not easily wetted with water and it is a difficult matter to make a uniform mixture of the two. It has been found that a number of substances — soap, oleic acid, glue, diatomaceous earth, flour, dextrin, etc. — when mixed with water and sulfur have the prop- erty of counteracting the mutual repulsion of sulfur and water with- out otherwise altering the nature of the sulfur. Certain of these sub- stances have been used in the preparation of commercial sulfur pastes or wettable sulfurs. These commercial pastes, as now manufactured, contain from 45 to 50 per cent of sulfur in a very finely divided con- dition, the remainder being water and one of the substances mentioned above. The effect of these pastes is that of dry sulfur. The usual strength to use is: Formula 13 Commercial sulfur paste 8 to 21 pounds Water 100 gallons Home-Made Wettable Sulfur. — A satisfactory wettable sulfur can be easily made at home by the use of glue water as follows : Formula 14 Powdered glue % ounce Hot water iy 2 gallons Sulfur (flowers or powdered) 5 pounds Water to make 100 gallons Dissolve the glue in hot water or soak over night in one and one-half gallons of cold water. Add the glue water to the sulfur a little at a time and work up into a smooth paste as free from lumps as possible. Rubbing is better than stirring. Wash this paste into the spray tank through a fine screen, using the remainder of the glue water to wash it through and a stiff brush to break up the remainder of the lumps. Then add plain water to make 100 gallons. Another formula more expensive than the above is : Formula 15 Make a paste of : Flour 4 pounds Water 4 gallons Mix this with : Sulfur (sublimed or powdered) 5 pounds Then add : Water to make 100 gallons Circular 227] PLANT DISEASE AND PEST CONTROL 57 The usual grades of sublimed or powdered sulfur may be wetted in the manner described in Formulas 14 and 15, but for the best results the finest grade of sulfur obtainable should be used. The sulfurs especially prepared for dusting are recommended for this purpose. Lime-Sulfur Solution. — This is the most active form in which sulfur compounds are commonly used in the control of insects or fungi. Its causticity prohibits its use on any foliage except that of the more hardy plants, and then in a very dilute form. Its principal use is as a dor- mant spray for the control of certain fungus diseases, scale insects, and a variety of other pests of deciduous trees. Commercial Lime-Sulfur Solution. — The horticulturists of the state are being supplied with concentrated commercial lime-sulfur solution of good quality and at reasonable prices. The great bulk of this im- portant pest remedy used in the state is therefore of commercial manu- facture, testing between 32° and 34° Baume. It is only necessary to dilute this with water before spraying. Home-Made Lime-Sulfur Solution. Formula 17 Stone lime 50 pounds Sulfur (sublimed or powdered) 100 pounds Water to make 50 gallons Heat about one-third of the total volume of water required. When the water is hot add all of the lime, and then immediately all the sulfur, which should previously have been made into a thick paste with water. After the lime is slaked another third of the water should be added, preferably hot, and the cooking should be continued until a clear orange-colored solution is obtained (usually 45 to 60 minutes), when the remainder of the water should be added, either hot or cold, as is most convenient. The boiling due to the slaking of the lime thoroughly mixes the ingredients at the start, but subsequent stirring is necessary if the wash is cooked by direct heat in a kettle. After the wash has been prepared it must be allowed to settle and then strained through a fine sieve as it is being run into the spray tank. The resultant product is a concentrated solution of lime-sulfur, which should be diluted about six times with water for a winter spray. Alkali Sulfides. — Sulfides of soda ("soluble sulfur") are sometimes used in place of lime-sulfur solution and have some advantages over the liquid preparations. 58 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION CRUDE PETROLEUM The use of crude petroleum is almost entirely limited to the winter spraying of deciduous trees when the buds are entirely dormant. It is generally applied from November to February. The crude oil emul- sion is especially recommended for black scale (Sarissetia oleae), Euro- pean fruit Lecanium (Lecanium corni), European or Italian pear scale (Epidiaspis piricola), cherry scale {Lecanium cerasorum) , and other scales infesting deciduous fruit trees. It is practically the only spray treatment which has been effective against the European or Italian pear scale, and will destroy the winter eggs of many of the aphids, of the red spider, and of some of the defoliating caterpillars. When crude oil is thoroughly applied it sometimes penetrates the fruit buds to a considerable extent, and may injure and even kill some of them. The great majority of the buds are not injured, however, but appear to be stimulated to a more vigorous growth, and to the production of foliage resistant to disease. It is good practice, especi- ally in dry seasons, not to apply crude oil emulsion until there is indication of swelling of the buds. A natural crude petroleum, testing about 23° Baume, is preferred, as it contains some of the lighter and more penetrating oils. Heavier crude oils have given satisfactory results, even those testing 18° and even lower. Kesidium oils (the residue of crude petroleum after the lighter portions have been distilled off) can be used if natural crude oil is unobtainable, provided their content of asphaltum is not too high to prevent their emulsification. Crude Oil Emulsion. Formula 18 Water 175 gallons Liquid soap 3 gallons Natural crude petroleum (21°-24° Baume) 25 gallons Partly fill the spray tank with water, add the liquid soap, agitate thoroughly, for one minute, add crude oil and continue the agitation, while running in the remainder of the water. If liquid soap cannot be obtained, use 20 pounds of fish oil soap dissolved in 10 gallons of boiling water to which 3 pounds of caustic soda or lye have been added. To kill moss or lichens on fruit trees, add 2 pounds of caustic soda or lye to the formula. During the spraying operation this emulsion should be thoroughly agitated and great care taken to wet all of the twigs. From 8 to 10 gallons should be used on a tree. Circular 227] plant disease and pest CONTROL 59 PETROLEUM DISTILLATES Kerosene, of about 40° Baume, has been used to a considerable extent as an insecticide, particularly on citrus trees, applied in the form of an emulsion. The cheaper, unrefined distillates have now largely replaced kerosene as a foliage spray. These are more effective as insecticides, so that smaller percentages can be used in the emulsions, but coupled with their superior insecticidal properties is their greater toxicity to fruit and foliage. The toxicity varies with climatic con- ditions, foliage injury being most certain in dry weather with a tem- perature of 95° F. or more. Unfortunately, the season when spraying is most effective against scale insects on citrus trees is often during the hottest and driest months. It seems impossible to guarantee im- munity from damage under all conditions with any of the distillates obtainable. Little injury to citrus fruit and foliage occurs in the coast regions where distillate emulsions have been used, but in the interior sections the use of this insecticide is very hazardous. Spraying with distillates, or with any other material, is not recom- mended as a substitute for fumigation in commercial citrus orchards, except in the case of young orchards, trees about dooryards, or where fumigation may not be convenient, or infestation may be light or limited to occasional trees. In such cases, Formula 19 is considered the most satisfactory. Kerosene emulsion is the safest of the petroleum-distillate sprays, although the most expensive. The "W. W." or "Water White" is a trade name of a low-grade kerosene and is safer than the usual grade of material sold as "distillate." The highly refined "case goods" kerosene has been found to cause the least amount of injury of any of the petroleum derivatives, but its cost is prohibitive except on a small scale. If much of the keorsene emulsion is allowed to run down the trunks of young trees, injury is likely to occur just beneath the surface of the ground. The following formula is intended for use on citrus trees : Kerosene Emulsion. Formula 19 Kerosene 15 gallons Liquid soap % gallon (Or hard soap 4 pounds) Water 200 gallons If liquid soap is available, it is preferable to hard soap, since no heating is required. Hard soap, preferably fish oil soap, is cut in thin 60 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION slices and dissolved in hot water. The soap is placed directly in the spray tank with 10 or 15 gallons of water or more (the exact amount is not important) and the engine then started. The oil is now added slowly, and the materials are emulsified by being run through the pump under pressure. After a few minutes the rest of the water may be added, and the spray is ready to be applied. Certain "tree" distillates, testing 31° to 32° Baume, said to be selected and partially refined, have lately displaced to a considerable extent the heavier distillates of 27° to 28° for use on citrus trees. "Tree" Distillate Emulsion. Formula 20 Tree distillate (31°-32° Baume) 4 gallons Liquid soap % gallon (Or hard soap 5 pounds) Water 200 gallons These materials are emulsified in the manner explained for the kerosene emulsion, Formula 19. If the distillate is used without soap, the following is the formula : Straight "Tree" Distillate. Formula 21 Tree distillate (31°-32° Baume) 4 to 6 gallons Caustic soda (95 per cent) 7 pounds Water 200 gallons In the case of the straight distillate, the oil is kept in suspension in the water by agitation and forms an unstable mechanical emulsion, which separates quickly on standing. In using this it is necessary to have the spray outfit equipped with a powerful and efficient agitator, which must be kept going continuously during the spraying operations. The use of petroleum-distillate sprays against black scale on olive trees is now being recognized as profitable. For this purpose the heavier distillates of 28° to 30° Baume, being more effective, are used, since olive foliage is very resistant to spray injury, and also because the spray can be applied through the winter months when low temper- atures and high humidities are the rule. Distillates of this density are also much used as a dormant spray on deciduous trees, although crude oil sprays are replacing distillates more and more for this purpose. Circular 227] plant DISEASE AND PEST CONTROL 61 Heavy Distillate Emulsions. — For use on olives, the following mechanical emulsion is recommended : Formula 22 Distillate (28° Baume) 7 gallons Caustic soda (95 per cent) 5 to 7 pounds Water to make 200 gallons First dissolve the caustic soda in a small amount of water and add to the water in the spray tank ; begin the agitation and slowly add the distillate, continuing the agitation during application. This spray will also remove lichens or moss from trees. If the amount of crude oil is reduced from 25 gallons to 15 gallons in Formula 18, the crude oil emulsion may be used on olive trees for the control of black scale. For use on dormant deciduous trees the following is recommended : Formula 23 Distillate (27°-28° Baume) 20 gallons Fish oil soap 30 pounds Water to make 12 gallons Dissolve the fish oil soap in water, heating it to the boiling point, add the distillate, and agitate thoroughly while the solution is hot. For use, add 20 gallons of water to each gallon of the above mixture. Commercial Prepared Emulsions and Miscible Oils. — Many grow- ers realize the difficulty in securing proper materials for home-made emulsions and the variability of the home-made mixtures even under the best conditions. They prefer to buy manufactured products, especi- ally when only small quantities are needed, but the commercial emul- sions and miscible oils are no more effective than a good home-made preparation and are only more convenient. These preparations are on the market in great variety, many being sold under trade names. Practically all grades of petroleum distillates, as well as crude petro- leum, are obtainable in a form ready to be used, after simple dilution with water. If these ready-made preparations are to be used, it is especially important to purchase only from reliable and well-known manufacturers or dealers. The commercial products in general are satisfactory for use for the purposes indicated for the above formulas. 62 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION The following is recommended for the control of thrips : Distillate Emulsion and Tobacco Extract. — Government formula. Formula 24 The government formula for the control of pear thrips is the following : Distillate emulsion . 10 gallons "Black Leaf 40" 1 pint Water to make 200 gallons When this formula was first prepared there were few commercial oil sprays on the market, so that it was necessary first to make a dis- tillate emulsion (Formula 23). In recent years there have appeared the miscible oils, which may be used as follows : Formula 24a Miscible oil 5 gallons "Black Leaf 40" 1 pint Water to make 200 gallons These formulas are for use against the adult "black thrips," and should be applied liberally as soon as any considerable number of in- sects are found upon the trees. Bo not fail to make daily inspections after the buds begin to swell. Applications should be repeated if neces- sary until the adults begin to lessen in numbers. In case the "white thrips" appear in destructive numbers later, the same formula may be safely used if the oil content is decreased and the nicotine increased as follows : Fobmula 246 Distillate emulsion 6 gallons "Black Leaf 40" 1% pints Water to make 200 gallons Formula 24c Miscible oil 3 gallons "Black Leaf 40" 1% P^ts Water to make 200 gallons For work with thrips, the greater force and volume delivery of the spray gun has rendered it superior to the spray rod, insuring not only a better but a quicker and easier job. The loss in material is more than overcome by the rapidity and ease of operation. Circular 227] plant disease and pest control 6H The resin wash is chiefly used for young and tender nursery stock, because it does not cause the injury often following the application of petroleum distillates. The preparation is : Formula 25 Resin . 10 pounds Caustic soda (76 per cent to 95 per cent) 3 pounds Fish oil 1% pounds Water to make 50 gallons To a gallon of hot water in an iron kettle add the fish oil and the resin, and heat until the latter is softened. After first dissolving the caustic soda in a small quantity of water add it and stir the mixture thoroughly. After this pour in enough water to make 50 gallons of spray material. Crude Carbolic Acid Emulsion. — For citrus trees. Formula 26 Fish oil soap 40 pounds Crude carbolic acid 5 gallons Water to make 40 gallons Dissolve the soap in hot water completely, add the carbolic acid and heat to the boiling point for twenty minutes (reserve some water to add in case the mixture begins to boil over). For use, add 20 gallons of water to every gallon of the above solution. The emulsion needs little or no agitation. CRUDE CARBOLIC ACID AND DISTILLATE EMULSION Formula 26a Fish oil soap (or liquid soap, 5 gallons) 40 pounds Crude carbolic acid (25 per cent) 5 gallons Distillate (27°-28° Baume) 5 gallons Water to make 50 gallons Prepare as with Formula 26, adding the distillate after the crude carbolic acid. This mixture is specially recommended for mealybugs on dormant deciduous fruit trees. Dilute 1 to 20 for use. TOBACCO PREPARATIONS Concentrated commercial preparations of tobacco have almost en- tirely superseded the home-made tobacco infusions on account of their greater convenience and uniformity. A material containing 40 per cent nicotine in the form of nicotine sulfate is recommended for the 64 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION preparation of contact insecticides containing nicotine. The usual formula is : Formula 27 Tobacco extract (nicotine sulfate, 40 per cent) 1 pint Fish oil soap 4 to 5 pounds Water 100 to 150 gallons For small quantities, use 1 teaspoonful to 1 gallon of water. Formula 21a Nicotine sulfate, 40 per cent 1 pint Dry billboard paste 2 pounds Water 150 gallons Make a paste of the dry material and add it to the water and nico- tine. This spray is intended for plants, like potatoes, tomatoes, etc., which are sensitive to soap mixtures. Tobacco Dust. — Finely ground tobacco dust finds some use as an insecticide, particularly in the control of aphids. Fifty per cent of kaolin or hydrated lime is sometimes mixed with it as a diluent. NICODUST AND COMBINATIONS Nicodust, invented and named by Professor Ralph E. Smith, is composed of a carrying substance, like finely powdered kaolin or lime, treated with a concentrated solution of nicotine sulfate, commercially known as "Blackleaf 40." The nicotine in such combination, especially with lime, becomes very volatile and is quickly driven off by heat. In this form therefore it acts largely as a fumigant, but may be effective as a contact poison as well. As soon as mixed, the dust should be packed in air-tight containers to retain the nicotine content. The best results in killing insects have been secured when the tempera- ture is over 70° F., and very poor results have followed its use in cold weather. The various strengths are usually denoted by the amount of "Blackleaf 40" contained, as follows: 2 per cent "Blackleaf 40," 4 per cent, 5 per cent, 6 per cent, 10 per cent, etc. A statement of the actual amount of nicotine is more accurate and is required in the guarantee of commercial preparations. The name nicodust does not belong exclusively to any particular mixture or company, but was originated as a convenient name for all mixtures of this sort. Arsenate of lead and sulfur are mixed with nicodust at the time of manufacture and give convenient combinations for treating different Circular 227] plant disease and pest control 65 types of insects or insects and fungus diseases at one application. Sulfur-nicodust, under actual field tests, appears to be more efficient in killing insects than ordinary nicodust containing the same percent- age of "Blackleaf 40." Thus in the control of the rosy apple aphis, a sulfur-nicodust containing 50 per cent of sulfur, 6 per cent of "Blackleaf 40," and 44 per cent of inert material gave far better results than a 6 per cent nicodust. The strengths commonly used are 2 per cent nicodust for walnut aphis and cherry or pear slug, 5 or 6 per cent for most of the aphids, thrips, etc., and a 10 per cent dust for the more resistant aphids such as the pea aphis. Nearly all of the hairy caterpillars, such as the tent caterpillars, webworms, thistle butterfly larvae, as well as the velvety cabbage worms, to which the nicodust adheres readily, are easily killed with a 6 per cent dust if applied while the caterpillars are quite young. Smooth caterpillars, like cutworms, on the other hand, do not readily succumb to any ordinary treatment with the material. Insects which are protected with a waxy or cottony material, like the woolly apple aphis, the mealy plum louse, mealybugs, etc., are not susceptible to nicodust at all, while those which have a wet or slimy covering, like the cherry or pear slug, or glandular hairs, like the walnut aphis, are easily killed with very weak nicotine contents. MISCELLANEOUS Corrosive Sublimate (Bichloride of Mercury). — This is a very poisonous substance and is one of the most powerful of germicides; it is employed to some extent in plant disease treatment. The usual strength is : Formula 28 Corrosive sublimate 1 ounce Water 8 gallons Or 1 part to 1000. Tablets to make this strength when added to 1 pint of water may be obtained at drug stores. Distilled or rain water should be used; the solution must not be kept in a metal container. It is also quickly spoiled by contact with clay or an organic substance such as the cut surface of potatoes. Another formula is recommended by Mr. C. F. Reimer for dis- infecting tools and cuts in pear blight control work. It will probably be found superior to Formula 28 for general tree work of this kind. 66 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION It is: Formula 28a Mercuric chloride 1 ounce Mercuric cyanide 1 ounce Water 4 gallons Or 1 part of each ingredient to 500. Whitewash. Formula 29 (Ordinary Formula) Water .. 2 gallons Quicklime 10 pounds Add more water after slaking to bring the wash to the desired consistency. A more durable whitewash : Formula 30 Quicklime 5 pounds Salt i/o pound Sulfur % pound Slake the lime slowly with water and add the salt and sulfur while it is boiling. Add enough more water to make a good wash. This is good for whitewashing the bodies of trees in the fall. In localities where there are deer this whitewash is not recommended, as the deer are said to be attracted by the salt it contains and injure the trees. Government Whitewash. Formula 31 Quicklime 40 pounds Salt - 15 pounds Rice flour 3 pounds Spanish whiting i/2 pound Glue - 1 pound Water 5 gallons Grafting Wax. — Many different combinations are used for this purpose, most of them being various combinations of beeswax and resin. The following formula is a good one : Formula 32 Resin 4 pounds Beeswax 1 pound Linseed oil 1 pint The ingredients are all melted and mixed together in a kettle. In hot weather use more resin. Circular 227] PLANT DISEASE AND PEST CONTROL 67 Some use one pound of tallow as a substitute for the linseed oil. One ounce of lampblack or one pint of flour is sometimes added. Asphaltum is used to some extent as a substitute for resin and bees- wax, and, in fact, straight asphaltum is used successfully in some cases for grafting wax. Carbon Bisulfide. — A liquid which evaporates quickly when ex- posed to the air, forming a heavy and inflammable vapor of great penetrating power. In using the material for fumigation, it is essen- tial that it be placed near the top of the room in a shallow container in order that the heavy vapors as they are given off may thoroughly diffuse through the air contained in the space to be fumigated. The proper amount to use depends upon the type of room being fumigated and ranges from 10 pounds to about 30 pounds to 1000 cubic feet in ordinary rooms where the walls and floor have not been made especially tight. The best results are obtained by doing this work when the temperature is above 70° F. Carbon bisulfide is one of the best agents for destroying ground squirrels that have failed to take poisoned grain, or having once sur- vived the poison refuse to take it again. It is most effective if used during the winter season when the ground is wet. The best methods of applying it are by the use of the "waste-ball" and of the "de- structor." The common waste-ball method is to pour a tablespoonful of carbon bisulfide on a piece of cotton waste, corncob, horse manure, or other absorptive material, and then to throw this as far down the hole as possible, closing the opening immediately with earth. Ex- ploding the gas with a torch before closing the opening is recommended where the ground is damp and there is no danger of fire. The ex- plosion of the gas forms new compounds which are poisonous and may diffuse somewhat more rapidly than the vapors of the material. The "destructor" pumps the vaporized carbon bisulfide into the burrow, and is said to be as effective as exploding the gas. Poisoned Barley. — Below is the latest government formula for preparing poisoned barley for California ground squirrels: Formula 33 Barley (clean grain) 16 quarts Strychnin (powdered alkaloid) 1 ounce Bicarbonate of soda (baking soda) 1 ounce Thin starch paste % pint Heavy corn syrup 14 pint Glycerin 1 tablespoonful Saccharin X 10 ounce 68 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Mix thoroughly 1 ounce of powdered strychnin and 1 ounce of common baking soda. Stir this into three-quarters pint of thin, hot starch paste and stir to a creamy mass. (The starch paste is made by dissolving 1 heaping teaspoonful of dry starch in a little cold water, and then adding it to three-quarters pint of boiling water; boil and stir constantly until a thin clear paste is formed.) Add one-quarter pint of heavy corn syrup and 1 tablespoonful of glycerin and stir thoroughly. Add one-tenth ounce of saccharin and stir thoroughly. Pour this mixture over 16 quarts of clean barley and mix well so that each grain is coated. Caution. — All containers of poison and all utensils used in the preparation of poisons should be kept plainly labeled and out of reach of children, irresponsible persons, and live stock. SPREADERS Spreaders are often added to sprays to give them a more even dis- tribution over the surface of the leaves and to prevent them from col- lecting into drops. Some of them also have insecticidal value and others act as adhesives. So much is claimed for these materials which is not fully warranted that many persons have come to feel that none should be recommended. However, the advantages gained should not be entirely overlooked, and we include here some of the more important substances used for these purposes. Casein. — This is a comparatively new material for use as a spreader and adhesive in sprays. It is a dry product which readily mixes in cold water and is put up in small or large containers. One and one- half pounds are sufficient for 200 gallons of the diluted spray. Casein is soluble only in alkaline solutions and is therefore worthless in acid insecticides and fungicides which are, however, seldom used. Flour Paste, Billboard Paste. — These materials are excellent spreaders and act as adhesives as well. They may be used with safety in all sprays, because they give no chemical reactions. Flour paste and certain of the dry billboard and paperhanger ? s pastes should be mixed in a small quantity of hot water before adding to the spray tank, and are somewhat difficult to handle. A specially prepared bill- board and paperhanger 's paste, known as "steamed paste," is already cooked, and as a wet paste mixes readily with cold water. It may be obtained in barrel lots or in small quantities from paint and paper dealers. The amounts to be used are as follows : Circular 227] PLANT DISEASE AND PEST CONTROL G9 Flour (cheap grade), 2 to 4 pounds to 200 gallons of dilute spray material. Dry billboard paste, 2 pounds to 200 gallons of dilute spray ma- terial. Steamed paste, 4 pounds to 200 gallons of dilute spray material. Glue. — As a spreader and adhesive, glue has long been used in sprays, and, like the flour pastes, may be used in all kinds of materials. Two ounces of dry glue dissolved in hot water are sufficient for 200 gallons of diluted sprays. Oil Emulsions and Miscible Oils. — Because of their penetration, these materials are often of value in carrying other materials, like nicotine. They should be used sparingly, about 2 gallons to 200 gallons of diluted spraying materials. When so diluted they have little value except as spreaders. Resin-fish oil soap (see Formula 10a) is often used with Bordeaux mixture. It is somewhat tedious to prepare and may now be purchased ready to use. This is very similar in character to the resin wash (see Formula 25). Soap. — This is one of the oldest and best known spreaders and is often used in sprays for this purpose as well as for an emulsifier and insecticide. As a spreader for such materials as arsenate of lead, for codling moth, use 5 pounds fish oil soap to 200 gallons of diluted spray material. V STATION PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION BULLETINS No. 185. 241. 246. 251. 253. 261. 262. 263. 266. 267. 268. 270. 271. 273. 275. 276. 278. 279. 280. 282. 283. 285. 286. 290. 294. 297. 298. 299. 300. 301. Report of Progress in Cereal Investiga- tions. Vine Pruning in California, Part I. Vine Pruning in California, Part II. Utilization of the Nitrogen and Organic Matter in Septio and Imhoff Tank Sludges. Irrigation and Soil Conditions in the Sierra Nevada Foothills, California. Melaxuma of the Walnut, "Juglans regia." Citrus Diseases of Florida and Cuba Compared with Those of California. Size Grades for Ripe Olives. A Spotting of Citrus Fruits Due to the Action of Oil Liberated from the Rind. Experiments with Stocks for Citrus. Growing and Grafting Olive Seedlings. A Comparison of Annual Cropping, Bi- ennial Cropping, and Green Manures on the Yield of Wheat. Feeding Dairy Calves in California. Preliminary Report on Kearney Vineyard Experimental Drain. The Cultivation of Belladonna in Cali- fornia. The Pomegranate. Grain Sorghums. Irrigation of Rice in California. Irrigation of Alfalfa in the Sacramento Valley. Trials with California Silage Crops for Dairy Cows. The Olive Insects of California. The Milk Goat in California. Commercial Fertilizers. The June Drop of Washington Navel Oranges. Bean Culture in California. The Almond in California. Seedless Raisin Grapes. The Use of Lumber on California Farms. Commercial Fertilizers. California State Dairy Cow Competition, 1916-1918. No. 302 Control of Ground Squirrels by the Fumi- gation Method. A Study on the Effects of Freezes on Citrus in California. I. Fumigation with Liquid Hydrocyanic Acid. II. Physical and Chemical Pro- perties of Liquid Hydrocyanic Acid. I. The Carob in California. II. Nutritive Value of the Carob Bean. Plum Pollination. Mariout Barley. Pruning Young Deciduous Fruit Trees. The Kaki or Oriental Persimmon. Selections of Stocks in Citrus Propagation. The Effects of Alkali on Citrus Trees. Control of the Coyote in California. Commercial Production of Grape Syrup. The Evaporation of Grapes. Heavy vs. Light Grain Feeding for Dairy Cows. Storage of Perishable Fruit at Freezing Temperatures. Rice Irrigation Measurements and Ex- periments in Sacramento Valley, 1914- 1919. 326. Brown Rot of Apricots. 328. Prune Growing in California. 329. A White Fir Volume Table. 330. Dehydration of Fruits. 331. Phylloxera-Resistant Stocks. 332. Walnut Culture in California. 333. Some Factors Affecting the Quality of Ripe Olives Sterilized at High Tem- peratures. 334. Preliminary Volume Tables for Second- Growth Redwoods. 335. Cocoanut Meal as a Feed for Dairy Cows and Other Livestock. 336. The Preparation of Nicotine Dust as an Insecticide. 337. Some Factors of Dehydrater Efficiency. 304. 308. 309. 310. 312. 313. 316. 317. 318. 320. 321. 322. 323. 324. 325. CIRCULARS No. No. 70. Observations on the Status of Corn 155. Growing in California. 157. 76. Hot Room Callusing. 153. 82. The Common Ground Squirrels of Cali- 159. fornia. 160. 87. Alfalfa. 161. 110. Green Manuring in California. 164. 111. The Use of Lime and Gypsum on Cali- 165. fornia Soils. 113. Correspondence Courses in Agriculture. 166. 114. Increasing the Duty of Water. 167. 115. Grafting Vinifera Vineyards. 168. 126. Spraying for the Grape Leaf Hopper. 127. House Fumigation. 169. 128. Insecticide Formulas. 170. 129. The Control of Citrus Insects. 130. Cabbage Growing in California. 172. 135. Official Tests of Dairy Cows. 173. 138. The Silo in California Agriculture. 174. 139. The Generation of Hydrocyanic Acid Gas 175. in Fumigation by Portable Machines. 144. Oidium or Powdery Mildew of the Vine. 176. 148. "Lungworms." 151. Feeding and Management of Hogs. 177. 152. Some Observations on the Bulk Handling 178. of Grain in California. 179. 153. Announcement of the California State Dairy Cow Competition, 1916-18. 181. 154. Irrigation Practice in Growing Small 182. Fruits in California. Bovine Tuberculosis. Control of the Pear Scab. Home and Farm Canning. Agriculture in the Imperial Valley. Lettuce Growing in California. Potatoes in California. Small Fruit Culture in California. Fundamentals of Sugar Beet Culture under California Conditions. The County Farm Bureau. Feeding Stuffs of Minor Importance. Spraying for the Control of Wild Morning- Glory within the Fog Belt. The 1918 Grain Crop. Fertilizing California Soils for the 1918 Crop. Wheat Culture. The Construction of the Wood-Hoop Silo. Farm Drainage Methods. Progress Report on the Marketing and Distribution of Milk. Hog Cholera Prevention and the Serum Treatment. Grain Sorghums. The Packing of Apples in California. Factors of Importance in Producing Milk of Low Bacterial Count. Control of the California Ground Squirrel. Extending the Area of Irrigated Wheat in California for 1918. CIRCULARS — Continued No. 183. Infectious Abortion in Cows. 184. A Flock of Sheep on the Farm. 185. Beekeeping for the Fruit-grower and Small Rancher or Amateur. 188. Lambing Sheds. 189. Winter Forage Crops. 190. Agriculture Clubs in California. 191. Pruning the Seedless Grapes. 193. A Study of Farm Labor in California. 198. Syrup from Sweet Sorghum. 201. Helpful Hints to Hog Raisers. 202. County Organizations for Rural Fire Con- trol. 203. Peat as a Manure Substitute. 205. Blackleg. 206. Jack Cheese. 208. Summary of the Annual Reports of the Farm Advisors of California. 209. The Function of the Farm Bureau. 210. Suggestions to the Settler in California. No. 214. Seed Treatment for the Prevention of Cereal Smuts. Feeding Dairy Cows in California. Methods for Marketing Vegetables in California. Advanced Registry Testing of Dairy Cows. 219. The Present Status of Alkali. 220. Unfermented Fruit Juices. 221. How California is Helping People Own Farms and Rural Homes. Fundamental Principles of Co-operation in Agriculture The Pear Thrips. Control of the Brown Apricot Scale and the Italian Pear Scale on Deciduous Fruit Trees. 226. Protection of Vineyards from Phylloxera. 227. Plant Disease and Pest Control. 228. Vineyard Irrigation in Arid Climates. 229. Cordon Pruning. 215. 217. 218. 222. 223 224.