UNIVERSITY OF CALIFORNIA PUBLICATIONS. COLLEGE OF AGRICULTURE. AGRICULTURAL EXPERIMENT STATION. SULFUR SPRAYS RED SPIDERS By W. H. VOLCK. BULLETIN No. 154 (Berkeley, June, 1903.) Red Spider, or Mite of the Almond. SACRAMENTO: SUPI 1903 BENJAMIN IDE WHEELER, Ph.D., LL.D., President oj the University. EXPERIMENT STATION STAFF. E. W. HILGARD, Ph.D., LL.D., Director and Chemist. E. J. WICKSON, M.A., Horticulturist, and Superintendent of Central Station Grounds. W. A. SETCHELL, Ph.D., Botanist. ELWOOD MEAD, M.S., C.E., Irrigation Engineer. R. H. LOUGHRIDGE, Ph.D., Agricultural Geologist and Soil Physicist. (Soils and Alkali.) C. W. WOODWORTH, M.S., Entomologist. M. E. JAFFA, M.S., Assistant Chemist. (Foods, Fertilizers.) G. W. SHAW, M.A., Ph.D., Assistant Chemist. (Soils, Beet-Sugar.) GEORGE E. COLBY, M.S., Assistant Chemist. (Fruits, Waters, Insecticides.) RALPH E. SMITH, B.S., Plant Pathologist. A. R. WARD,B.S.A.,D.V.M., Veterinarian, Bacteriologist. E. H. TWIGHT, B.Sc, Diploma E.A.M., Viticulturist. E. W. MAJOR, B.Agr., Dairy Husbandry. A. V. STUBENRAUCH, M.S., Assistant Horticulturist and Superintendent of Substations. WARREN T. CLARKE, B.S., Assistant Field Entomologist. H. J. QUAYLE, B.S., Assistant Entomologist. H. M. HALL, M.S., Assistant Botanist. GEORGE ROBERTS, M.S., Assistant Chemist, in charge Fertilizer Control. C. A. TRIEBEL, Ph.G., Student Assistant in Agricultural Laboratory. C. A. COLMORE, B.S., Clerk to the Director. EMIL KELLNER, Foreman of Central Station Grounds. JOHN TUOHY, Patron, ) y Tulare Substation, Tulare. JULIUS FORRER, Foreman, ) R. C. RUST, Patron, ) V Foothill Substation, Jackson. JOHN H. BARBER, Foreman, ) S. D. MERK, Patron, ) y Coast Range Substation, Paso Robies. J. H.OOLEY, Workman in charge, ) S. N. ANDROUS, Patron, ) ( Pomona y Southern California Substation, < J. W. MILLS, Foreman, ) ( Ontario. V. C. RICHARDS, Patron, T. L. BOHLENDER, in charge, ROY JONES, Patron, WM. SHUTT, Foreman, y Southern California Substation, ■] 1 y Forestry Station, Santa Monica. The Station publications (Reports and Bulletins), so long as available, will be sent to any citizen of the State on application. SULFUR SPRAYS FOR RED SPIDERS. The present Bulletin is based on the results obtained in the cooperative investigations of the Los Angeles County Board of Horticultural Commissioners, the Sutter County Board of Horticultural Commissioners, and the Entomological Department of the Experiment Station. Mr. Volck, a student in entomology at the University, working under the direction of the Entomologist, served as inspector in the two counties while the investigations here reported were being conducted. Special acknowledgments for assistance are due to Mr. J. W. Jeffreys, secretary of the Los Angeles Board ; to Messrs. Payne and Seeley, Horticultural Inspectors of Los Angeles County ; and to Messrs. Stabler, Kells, and Hull, Horticultural Commissioners of Sutter County. The formulae now offered seem to meet all the requirements for the successful control of these pests on both citrus and deciduous trees. C. W. WOODWORTH. Red spiders (a family of plant-feeding mites) appear as minute brownish-red, red, or yellow specks, found either moving about over the surface of the leaves or resting in protected places on the stems. Their eggs can easily be seen with a magnifying glass. In the case of I J FIG. 1. The Eggs, Shed Skins, and Molting Forms of the Red Spider of the Almond. the red spider of the orange, they will be found in numbers along the mid-rib on the upper side of the leaves, but are often found elsewhere. They are round, red before hatching, and white afterward. The eggs of the almond Bryobia are also red, but are usually deposited on the stems. The larger white specks and masses found on leaves and stems infested with mites, are composed of the shed skins of the young mites, for they molt several times before reaching the adult stage. 4 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. Mites feed by sucking; they pump out the more liquid parts of living cells and the chlorophyll or green bodies suspended in them. As the injury proceeds, the leaves become whiter and are finally killed and fall to the ground. THE USE OF SULFUR. Ever since the control of mites has been attempted, sulfur in various forms has been one of the principal remedial agents employed. This use of sulfur antedates entomological records, and the persistency with which it has been followed is a strong indorsement of its efficiency. Sulfur has been found especially adapted to the treatment of mites feeding on living plants, first, because of its efficiency in destroying the mites; and, second, because of its very neutral behavior toward foliage. Our own experiments were made on two species of mites commonly called red spiders, belonging to different genera — the Bryobia of the almond and other deciduous trees, and the Tetranychus on orange, which has also been called the purple orange mite. The orange mite is best adapted to experimental work, since it devel- ops readily in cells constructed on oranges or other citrus fruits. Mites were inclosed in cells with very small amounts of sublimed sulfur, and check cells were provided in which no sulfur was placed. In every case the mites inclosed with sulfur either died shortly after exposure, or laid a few eggs which, while hatching, never reached maturity. In the check cells, however, the mites prospered as long as the food supply lasted. The record of one of these experiments is inserted here to show the gradual manner in which sulfur acts — some time elapsing after applica- tion before the full effect is obtained. On the 20th of October, 1902, mites were inclosed in seven cells, four of which were checks and three contained a small amount of sulfur. On the 18th of November 18 per cent of mites were alive in the sulfured cells, while in the checks 64 per cent were still alive. The average number of eggs laid in the sulfured cells was nineteen, while in the checks it was fifty. Similar experiments were also tried with foliage. Small mite-infested branches were dusted with sublimed sulfur and inclosed in paper bags without severing from the tree. In less than a month, the only traces of living mites were a very few eggs and newly-hatched young. DRY SULFURING. Dry sulfuring, or dusting with ground or with sublimed sulfur, has been the usual method of application. The conditions determining the success of dry sulfur are, first, the thorough distribution of the material over the entire surface of the tree; and, second, the retention of this sulfur for a period sufficient to allow it to act both on the mites present SULFUR SPRAYS FOR RED SPIDERS. 5 at the time of application, and on those which will hatch from the eggs always to be found in large numbers on infested plants. With dry sulfuring these conditions are often but imperfectly met. The retention of sulfur offers the greatest difficulty. It is best accom- plished by dusting the trees when they are wet with dew, but even then the results are not always satisfactory, since large areas of the foliage may become nearly free from sulfur, again allowing the mites to increase. Therefore, dry sulfuring, as generally practiced, can only be regarded as a method of partial control, and has proved a failure in certain refractory oases ; indeed, it has seldom been at all successful against the red spider of the orange in southern California, because this mite does most of its work in the fall, winter, and spring, when rains and winds greatly reduce the chances of dry sulfur adhering long enough to be effective. It is evident that neglecting to apply the sulfur thoroughly when the trees are wet will greatly reduce the chances of success, and may often result in failure. The practice of dusting the ground under the trees, or dusting the spider webs found on the ground, will have little or no effect. Our red spiders lay their eggs and spend their entire life on the infested plants. As far as we have been able to ascertain, they do not intentionally go to the ground at any time, but when they become very numerous on infested trees, they may be knocked off or fall with the dropping leaves in sufficient numbers to be noticeable on the ground, where, without doubt, the great majority die of starvation, being unable to find their way back to the tree. The web found on the ground, and the greater part of that on the trees, is the work of true spiders and not mites; these true spiders catch insects and are beneficial. The above remarks refer to the red spiders of the almond and orange and most other mites, but it may be that the Tetranychus, which is known as the yellow mite, spends the winter on native green plants, ascending the trees in the spring. SULFUR SPRAYING. Our attention was first called to the advantages of the wet method of applying finely divided sulfur by a grower at Upland, who mixed sulfur into water by constant agitation and applied it as a spray to a considerable number of orange trees, with very satisfactory results. The distribution had been much better than was possible with a dusting method, but the adhering qualities were not good. It was evident that if this difficulty could be overcome, much might be expected of this spray as a remedy for mites. Several adhesive materials were added to the mixture. Lime, which has long been used in paris green work, was rejected because of the bad appearance produced when used on citrus trees. After numerous trials 6 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. flour paste prepared according to a definite formula was adopted. If the flour-paste spray has sufficient time to dry, it withstands rain and winds very well. Prolonged rains will cause some shifting of the sulfur particles, but these set again on drying. Sulfur alone requires some time for its complete effects to develop, so if rapid disinfection as possible is desired it can be used in connection with some contact insecticide. For this purpose sulfid of potash has proved best adapted; it kills by contact, but has no lasting effect. THE TREATMENT OF THE ORANGE MITE (RED SPIDER). The orange tree is very difficult to treat satisfactorily, and very few sprays are adapted to citrus conditions; the difficulty being the danger of injuring the fruit rind or the leaves, or both. Even dry sulfur may be harmful if applied in such a manner as to leave large blotches lodged on the young fruit, in which case serious burning of the rind may result. FIG The Red Spider of the Orange. The injury is doubtless due to the presence of sulfuric acid in the sulfur. All powdered sulfur contains more or less sulfuric acid, owing to gradual oxidation by contact with the air. In the preparation of the sulfur spray for the orange mite the acid may be neutralized with a small amount of lime or better, by the addition of sulfid of potash. During the fall and winter of 1902 the writer treated about one hun- dred orange trees, that were affected by the mite, with the sulfur spray. The results were entirely satisfactory, as the trees and fruit were not injured by the application, while the mites were very greatly reduced, and possibly exterminated in some cases. Both sublimed and ground sulfur were used with good results. Some- what more ground sulfur was required, since part of it is in very coarse SULFUR SPRAYS FOR RED SPIDERS. / particles, and so not available; the amounts of sulfur varied between 10 and 20 pounds to 100 gallons of water. It was found that 15 pounds of sublimed sulfur per 100 gallons were ample as a fall or winter wash, while 10 pounds would do just as well in the spring, after the danger of prolonged rains is over. The proportion of paste found most satisfac- tory was at the rate of 4 pounds of wheat flour to 100 gallons of water. Much more than this causes loss by scaling off of the paste film, and a less amount will not be sufficient to stick the sulfur. The lime used to neutralize the acid was slaked and strained and not more than 1 pound used to 100 gallons of spray. The application of this spray was very thorough; the trees were large Navels, and an average of 13 gallons of spray was used. Great care was taken to wet the under sides of the leaves and fruit, as well as the stems and interior. Some of the trees treated were under observation for over a month, and passed through heavy rains without material loss of sulfur. The trees were not sprayed in a solid block, but alternate rows were taken, so that untreated trees remained throughout the treated area. The result was that in less than a month the treated trees were practically clean, while the checks were still well-infested. Some attention was paid to the removal of the sulfur from the fruit, and it was found that dry brushing, as ordinarily practiced to clean off dust, was sufficient. Since the work at Azusa was completed the horticultural inspector at Monrovia has used this spray on a larger number of trees, and reports very perfect results. It ma}' be added that the sulfur spray prepared by the formula used has, so far as observed, no injurious effect on the tree or fruit, and can be applied at any time without danger. SULFUR SPRAYING FOR THE ALMOND MITE (RED SPIDER ). The red spider of almonds and prunes is a serious pest in the interior valleys of California, but in general dry sulfuring has proved sufficiently effective to keep it in check, and where persisted in, whether the spider is present in numbers or not, has resulted in the practical cleaning up of some orchards. While this is true in general, there are a few cases in which dry sul- furing has proved a failure. The most refractory case known was that of the McMilin almond orchard in Sutter County ; and owing to the cooperation of the County Board of Horticultural Commissioners, we have been able to test, on an entirely different mite and under different climatic conditions, the formula developed in southern California. The red spider of the almond is larger and harder-bodied than the orange species, and experiments have shown it to be about four times as resistant to insecticides. For this reason and also because the mites were very numerous and doing a large amount of injury every day, it was decided to use sulfid of potash with the sulfur spray. 8 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. Two gallons of the stock solution (made according to. the formula given below) were used to 100 gallons of mixture. The paste was used in the same proportions as in spraying orange trees. Sublimed sulfur was used in two strengths — 10 and 20 pounds to 100 gallons of mixture. Every effort was made to spray the trees thoroughly on both the upper and lower surfaces of the twigs and leaves. Trees, 15 to 20 feet in diameter, received from 8 to 12 gallons of spray; the trees were in full leaf, so the amount was not excessive. This entire orchard was treated and the work has now been under observation for over a month. The injury being done by the mite was stopped at once, the majority being killed. The adults all died in about fifteen days. Very few eggs remain, and the sulfur is killing the young as fast as they hatch ; in fact, it seems as if complete disinfection of many trees would result. At the time of spraying, the leaves of many of the trees were bleached out by the constant work of the spider; since the spraying, the color of these affected leaves has improved until many of them can not be recog- nized as mite-injured. This is due to the fact that mites feed by suck- ing, and their mouth parts are so small that they can puncture the cells of the leaf and draw off the more fluid portions, including the green matter, without killing them. Microscopic sections of leaves very badly injured by mites show the cells to be intact, except that most of the chlorophyll granules have been removed. These results show that the foliage can be saved even in very advanced cases of mite injury. THE SULFUR SPRAY COMPARED WITH DISTILLATES. Contact sprays can not compare with the sulphur spray as a remedy for mites, for when properly applied, the sulfur spray remains active for a sufficient length of time to kill the young as they hatch from the egg, and may, as before stated, result in complete disinfection. Of the contact sprays, the distillates are perhaps the most efficient, and the eggs of the red spider of the orange are readily killed by them. But no matter how thorough the application, some mites and eggs will escape contact with the spray mixture; the mites thus left, because of their wonderful reproductive powers, will soon increase, making another treatment necessary. This repeated treatment with oily sprays will prove injurious to the trees, and is not advisable if a better remedy is available. The effects of sulfur on higher plants is so slight, if any, that it has never been serious enough to attract the attention of the most careful observers. There are two theories to explain the insecticidal and fungicidal properties of sulfur. The action is most probably due to the vapor of sulfur; others attribute it to that vapor being oxidized, by the action of SULFUR SPRAYS FOR RED SPIDERS. 9 the air, into sulfurous acid. The deadly properties of sulfurous acid, or sulfur smoke, are well known, and it is usually considered to be more fatal to plant than to animal life. Whichever theory is correct, it is quite certain that the sulfur has to evaporate before it becomes effective; therefore the larger the evaporating surface, the better the result. The evaporating surface of a substance is enormously increased by pulverizing it into a fine powder, and the finer the powder the greater the surface. There is no reason why the ground sulfur should not be as good as the sublimed, if the pulverization were as fine; but the ground sulfur on the market is composed of some particles very much finer than the particles of sublimed sulfur, and many others vastly coarser. If these large particles were bolted out and repulverized, an article supe- rior to sublimed sulfur might be produced. GROUND. SUBLIMED. FIG. 3. Photo-micrograph of Ground and Sublimed Sulfur. The left side of the accompanying illustration shows the irregular lumps and particles of ground sulfur; the right side shows the uniform globular bodies of sublimed sulfur collected in small masses. If the efficiency of sulfur depends on the part vaporized, it is evident that good results demand the retention of the vapor. This could be accomplished by placing a tent over the tree, as in cyanide fumigation; but the time required for sulfur to affect mites is so great, that this is impracticable. The same result can be obtained by a uniform and thorough distribution of the sulfur particles over the surface of the tree; when this has been accomplished, the mites will always be in close proximity to particles giving off vapor. 10 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. PREPARATION OF SULFUR SPRAYS. The ingredients of the sulfur sprays are prepared as follows: Flour Paste. — Take one pound of wheat flour to one gallon of water. Place the flour in a box with a screen bottom (common window screen- ing), and pour the water through it, until all the flour has been washed into the receiving vessel. It will then be finely divided and free from lumps. The mixture should then be brought to the boiling point, being stirred constantly, thus forming a thin paste, without lumps. The paste is conveniently made in 20-gallon lots, using the common 25-gallon kettles so often found on California ranches; if large kettles are not available, the paste can be boiled in less water and then diluted to the above proportions before cooling. The paste should be strained before using. Sulfid of Potash Stock Solution. — Granulated, or powdered concen- trated lye, 15 pounds; sulfur, 18 pounds; water to make 20 gallons. Stir the sulfur and lye together in a vessel which will allow plenty of room for boiling. When well mixed, add about one pint of water, placing it in a slight hollow in the mixture, and stir in slowly. The mixture will soon begin to melt and boil, forming a red fluid; stir until the boiling ceases, and then add water to make 20 gallons. This stock solution will keep for awhile, or indefinitely when protected from the air. Preparation of the Spray Mixture with Sulfid of Potash. — Place 10 to 15 pounds of sublimed sulfur, or 14 to 20 pounds of ground sulfur in the spray tank with 4 gallons of flour paste and 1 to 2 gallons of the sulfid of potash stock solution; add water to make 100 gallons. For summer or spring spraying after the danger of rains is over, the minimum amount of sulfur is sufficient. Without Sulfid of Potash. — Made as before, except that the sulfid of potash is omitted. The sulfid of potash is not necessary to kill the red spider of the orange, but will neutralize any sulfuric acid that may be present. One gallon of the stock solution will be sufficient. It can be omitted with the red spider of the almond if the application be made in time; that is, before the injury has become very serious. The ingredients of the sulfur spray must be kept constantly and strongly agitated while in use. A common garden hoe is a good instru- ment to stir with in hand outfits, especially where the opening in the tank is small. When used to agitate the mixture the blade of the hoe should be turned up, but when used to scrape the sulfur from the bottom of the tank the blade should be held down as in hoeing. A power outfit provided with a mechanical agitator is very desirable in working with this spray. SULFUR SPRAYS FOR RED SPIDERS. 11 Spray Nozzles. — In our experience nozzles of the plug-cock type, which can be cleaned by the simple turning of a valve, are best adapted for the sulfur spray. Method of Spraying. — Much of the success of any spraying operation depends upon the thoroughness of the application. With the sulfur spray, every effort should be made to wet both the upper and the lower surfaces of both leaves and twigs and also the interior of the tree. This is best accomplished by beginning at the top and working the spray well through the upper branches, finishing with the lower parts. This method should be followed around the tree, lapping well over the section sprayed at the beginning. The sulfur spray is cheap, and material should not be spared. A symmetrical almond tree 20 feet in diameter will take from 12 to 14 gallons of spray, and an orange tree of the same size, from 14 to 18 gallons. SUMMARY. The old idea that sulfur is a good remedy for mites is fully supported by recent experiments. Dry sulfur is usually successful as a method of partial control. Sulfur spraying has been found many times more efficient than other methods of application and is perfectly successful where dry sulfuring has failed. The efficiency of the sulfur spray has been demonstrated for the red spider of the orange (Tetranychus mytilaspidis) in southern California, and for the almond Bryobia in Sutter County. REPORTS AND BULLETINS AVAILABLE FOR DISTRIBUTION. REPORTS. 1896. Report of the Viticultural Work during the seasons 1887-93, with data regarding the Vintages of 1894-95. 1897. Resistant Vines, their Selection, Adaptation, and Grafting. Appendix to Viti- cultural Report for 1896. 1898. Partial Report of Work of Agricultural Experiment Station for the years 1895-96 and 1896-97. 1900. Report of the Agricultural Experiment Station for the year 1897-98. 1902. Report of the Agricultural Experiment Station for 1898-1901. BULLETINS. No. 115. Remedies for Insect and Fungi. (Revised.) 121. The Conservation of Soil Moisture and Economy in the Use of Irrigation Water. 125. Australian Saltbush. 127. Bench-Grafting Resistant Vines. 128. Nature, Value, and Utilization of Alkali Lands. 129. Report of the Condition of Olive Culture in California. 131. The Phylloxera of the Vine. 132. Feeding of Farm Animals. 133. Tolerance of Alkali by Various Cultures. 134. Report of Condition of Vineyards in Portions of Santa Clara Valley. 135. The Potato-Worm in California. 136. Erinose of the Vine. 137. Pickling Ripe and Green Olives. 138. Citrus Fruit Culture. 139. Orange and Lemon Rot. 140. Lands of the Colorado Delta in Salton Basin, and Supplement. 141. Deciduous Fruits at Paso Robles. 142. Grasshoppers in California. 143. California Peach-Tree Borer. 144. The Peach-Worm. 145. The Red Spider of Citrus Trees. 146. New Methods of Grafting and Budding Vines. 147. Culture Work of the Substations. 148. Resistant Vines and their Hybrids. 149. California Sugar Industry. 150. The Value of Oak Leaves for Forage. 151. Arsenical Insecticides. 152. Fumigation Dosage. 153. Spraying with Distillates. Copies may be had by application to the Director of the Experiment Station, Berkeley, California.