CALIFORNIA AGRICULTURAL EXTENSION SERVICE CIRCULAR 45 June, 1930 ZINC CHLORIDE TREATMENT FOR PEAR BLIGHT CANKERS LEONARD H. DAY Cooperative Extension work in Agriculture and Home Economics, College of Agriculture, University of California, and United States Department of Agriculture cooperating. Dis- tributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. B. H. Crocheron, Director, California Agricultural Extension Service. UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE BERKELEY, CALIFORNIA Digitized by the Internet Archive in 2011 with funding from University of California, Davis Libraries http://www.archive.org/details/zincchloridetrea45dayl ZINC CHLORIDE TREATMENT FOR PEAR BLIGHT CANKERS LEONAED H. DAY* INTRODUCTION The supply of Extension Circular 20, "Pear Blight Control in California, ' ' is exhausted and the circular cannot be republished until later. This circular is being issued on account of the present serious epidemic of pear blight in California. It also replaces the recent supplement to Circular 20 entitled "Further Suggestions for Pear Blight Control." Since the "zinc chloride" treatment was first introduced, con- siderable new information has been secured regarding its use in arrest- ing pear blight cankers. This method is the most effective way we now have to save trees affected with blight. It has been used with success by many growers over a period of three to five years. It is highly important however for the grower to understand that the zinc chloride solution must be properly applied, and that the treat- ment has its limitations. Without a proper appreciation and under- standing of these matters, the grower will be disappointed with results. Zinc chloride is intended primarily for new cankers on large branches and trunks. However, it can be used on small branches to advantage in saving fruit if the operators have time to apply it. But in trying to save fruit in the tops of trees the solution dropping on fruits below may blemish as many fruits as are saved by the treat- ment. This material is applied to blight cankers on large branches without surgery, other than cutting off blighted twigs in the infected area of the bark. NATURE OF THE ZINC CHLORIDE TREATMENT Blight travels at first in the outer bark without affecting the most vital portion of the tree, the cambium layer. That is the reason the canker can be cured with zinc chloride solution and the branch saved even though the blight may extend completely around the branch. After the cankers are one or two weeks old the blight runs * Assistant Pomologist in the Experiment Station. 4 California Agricultural Extension Service [Cerc. 45 deeper and then the solution also may penetrate deeper and kill the cambium layer under the diseased bark. Therefore, the earlier the treatment is applied, the better. The diseased bark is more absorptive of the zinc chloride solution than is healthy bark. In trunks and large scaffolds, however, even old cases are frequently cured and the parts saved. The zinc chloride treatment is not 100 per cent efficient ; but with careful work 85 to 98 per cent of the cankers treated can be cured, and if the cankers are new the branches can be saved. The percentage of cure is much less in the case of old cankers than with new ones. ZINC CHLORIDE TREATMENT OF BLIGHT IN DIFFERENT VARIETIES OF PEARS Most of the experience with control measures has been with the Bartlett variety. Other common commercial varieties respond to treatment in about the same way, except that the bark in the Easter Beurre and Beurre Hardy is perhaps less easily penetrated by zinc chloride and in the Bosc a little more easily penetrated. The disease runs so freely in Bosc, Glout Morceau and Beurre Hardy that the operator often does not detect the limits of the disease and hence fails to apply the material a sufficient distance along the branch. Rains occurring within a day after application sometimes wash off much of the solution, so these cases should be nagged for future observation. EQUIPMENT AND GENERAL PLAN OF WORK Each operator will require a pair of long-handled shears, a saw, a jar of each strength of zinc chloride solution to be used, paint brushes, a ladder, and a knife. It is well also to have at hand a small canteen or bottle of water and a damp towel for occasionally wiping zinc chloride off the hands; or, if a drop splashes in the eyes it can be washed out with water. A small bucket is handy for carrying some of this equipment. In cutting off blighted twigs the shears must be kept disinfected. It is also important to disinfect all cuts on trunks and main branches, but during an epidemic this operation consumes too much time to warrant disinfection of cuts on smaller branches. The zinc chloride solution can be used for disinfecting the shears and cuts on trunks and scaffolds. The shear blades should be kept thoroughly wet with the solution. The 53 per cent solution is pre- 1930] Zinc Chloride Treatment for Pear Blight Cankers 5 ferable because it is more syrupy than the others and hence will stick to the shears longer than the weaker solutions. If, in an emergency, the grower has not sufficient men to cut out the twig blight and at the same time to treat all of the cankers on main branches every week or ten days, the following procedure is advised : first, go over the orchard and cut off all blighted spurs and twigs on the scaffold branches within 5 or 6 feet of the ground. After cutting off a diseased twig or spur where there is danger that the infection has already entered the main branch, zinc chloride should be applied to the bark 8 or 10 inches above and below the cut. If the disease is already visible in the branch the solution should be applied for a foot or more, up and down the branch, beyond any visible signs of the blight in the bark. The solution should be applied completely round the branch in this latter case. While treating these scaffold branches the operator should also treat in the same manner cases on side branches out for several feet, the distance depending on how many minutes the operator may spend on each tree and yet cover the orchard within a week or ten days. This treatment should be repeated over the whole orchard a second time, but this time with a ladder to reach still higher upon scaffold branches and to follow the side branches out to a practical distance. The third time the orchard is gone over the twig blight may be cut out, Off-season blossoms should also be removed during this last operation. If the weather has been favorable, many of the infections in twigs and smaller branches will by this time have dried up, and much heavy pruning will thus be avoided. The details of the procedure will of course, vary according to the age and size of the trees and the number of competent men available. All twigs and spurs within a cankered spot on a branch must be cut back to stubs about an inch long, for if the twigs are cut off close, the solution will kill a small spot of the cambium layer round each cut and thus may kill the branch. Also these stubs serve as indicators to show later where zinc chloride has been used. All except the cut ends of the stubs must be covered with the solution. It is not safe to leave twigs, spurs, or leaves in the blighted area of bark, because blight bacteria may have already progressed into them, even though they may appear healthy. If active blight has run down a twig to within 6 or 8 inches of its attachment to the scaffold, zinc chloride should be painted onto the scaffold for 8 to 10 inches above and below the cut. In the case of new sucker growths, the blight may extend one foot or more below the point where the twig has turned dark. 6 California Agricultural Extension Service [Circ. 45 In cutting twig blight towards ends of branches the operator should, if possible, make the cut back into wood one or two years older than the affected tip. Blight may run downward in twigs and small branches at a rate of a fraction of an inch to six inches or more per day. Suckers and succulent shoots in the lower parts of trees should not be removed during the blight season for the reason that the disease gets into the fresh wounds. Only after a sucker growth becomes diseased should it be removed. After removal of the diseased sucker or shoot the bark should be treated with zinc chloride of the proper strength. Beginning about the middle of May inspection of the lower parts of trees for body blight should be made throughout the summer every week or ten days, by careful examination of the trees and gouging into suspicious looking areas in the bark. This should not cease during the harvest season. All inspection cuts should be disinfected with zinc chloride (33 per cent). Zinc chloride keeps the cuts disin- fected a much longer time than do other disinfectants commonly used. The zinc chloride solution makes reddish spots and streaks within the bark and sometimes causes a watery condition in the canker and may cause gum to ooze out upon the surface. After a little experience the operator can usually distinguish this from active blight. However, to make later inspections more accurate on trunks and main branches it is very important to drive in a small nail at each end of the zinc chloride treatment. The nails will then be about one foot from each end of the canker. This will also aid the manager in correcting mis- takes of the operators. In determining the extent of the canker to be treated, only a few small inspection cuts should be made in the bark because the solution will kill a small spot of bark to the wood wherever a wound has been made. In applying zinc chloride to a canker near the end of a large branch which is cut back to a point free from blight, leave several inches untreated at the end, because the solution usually kills buds at the end of stubbed branches. The greatest loss of trees from blight usually occurs during the summer and fall. These losses are from infections which get into the trunks and lower parts of the scaffold branches. In May and June both rain and insects carry the disease down from the blossom and twig infections above into new shoots, pushing buds, wounds and growth cracks about the lower parts of the tree. On many of the trees these infections do not enlarge until July or August. In some 1930] z INC Chloride Treatment for Pear Blight Cankers 7 years these body infections occur chiefly after harvest season when new buds push out in the lower parts of the tree and off-season blos- soms open. INSPECTION OF TREATED CANKERS In inspecting treated cankers it is important to remember that the blight color inside of the cankered area often does not disappear for some weeks after the treatment. The best plan is to consider a treated canker dead or dying as long as active blight does not begin to run beyond the ends of the canker and into or beyond the healthy bark showing zinc chloride blotches. In this connection the nails mentioned above are of great assistance for if active blight is not found in the areas between the nails and the ends of the canker (or beyond the nails) the case can be considered as probably cured. It is not known how long the bacteria live in the cankers following the treatment. Frequently in old cankers a small spot of live blight can be found in the canker a month or two following the treatment but this infection seldom is able to work through the zinc chloride in the bark, and the disease finally dies out. The cure of the canker is thus seen to often be a rather slow process. The important thing then is merely to watch for cases in which the disease does creep out beyond the ends of the treated canker. Many valuable branches have been cut off by operators who did not understand this point. Operators are apt to worry about cases which become sappy or that bleed or ooze out gum following the treatment. This is not a sign of blight but is almost invariably the effects of the zinc chloride. In re-treating cases in smooth-barked branches it is better to use a weaker solution than that used the first time, unless the disease has run beyond the marking nails or beyond the zinc chloride spots in case nails were not used. A second treatment often penetrates too deeply into the old treatment on smooth-barked branches and kills the cambium layer. Growers are apt to be unduly concerned about uncured cankers spreading the blight to other trees. All evidence seems to indicate that there is little danger from this. There is apparently very little long-distance carrying of blight after the blossoming season is over and throughout the summer and fall. Fall and winter cases are often very deep before discovered, and in some cases small spots of blight may remain within the canker for a long time after treatment but nearly always die out by February. 8 California Agricultural Extension Service [Cntc. 45 A few weeks before the blossoming time all treated cankers should be inspected and if spots of active blight are found the canker should be re-treated. Cured cases often become sappy at this time of the year and this, along with a pinkish cast to healing bark and to regenerating cambium, and reddish streaks in the bark and wood are apt to be confusing until the operator learns to distinguish these conditions from the color of active blight. Re-treating at this time is very effect- ive in stopping blight. Some growers have feared that there would be so many zinc chlo- ride cases awaken at blossoming time that it might be a serious source of blossom blight. Observations over several years indicate that very little blossom blight originates in this way. In the present epidemic the orchards in which zinc chloride was used during the previous year have, if anything, less blossom blight than the average neighbor- ing orchards in which zinc chloride was not used. There are prob- ably so many small infections in the orchard, not discovered and not treated, that the few treated cases that were not cured do not consti- tute much extra hazard. Zinc chloride treatment has been of great value in saving the fruit on large branches even if the blight cankers on the lower part of the branches have already killed the cambium layer before the treatment is made. Such treatments made five or six weeks before harvest usually allows the fruit to mature before the branch withers, and the blight is permanently arrested. With a little observation leaves and tender shoots burned with zinc chloride can be distinguished from those affected by blight. Blighted twigs, fruits, and leaves are usually darker in color, more watery, more glossy and usually have small beads of gum upon the surface. DIRECTIONS FOR PREPARING ZINC CHLORIDE Three strengths of solution are used, depending upon the age and size of the branch and the time of year. The strongest solution con- tains 53 per cent by weight of zinc chloride powder, and 47 per cent by weight of a solvent consisting of denatured alcohol, water, and hydrochloric acid. The medium strength contains 43 per cent zinc chloride and the weakest one contains 33 per cent zinc chloride. These solutions may be purchased already prepared, or may be mixed at home according to the following directions. 1930] Zinc Chloride Treatment for Pear Blight Cankers Formula for 53 per cent solution To 2 pints hot water add 3 ounces concentrated hydrochloric acid and dissolve in this 9 pounds of dry zinc chloride powder, using an enameled kettle. If the powder does not dissolve readily, the mix- ture may be brought to the boiling point on the stove. The water and acid solution of zinc chloride should then be poured into 7 pints of denatured alcohol. Since alcohol is combustible it must not be brought near the stove. Formula for 43 per cent solution To 2 pints hot water add 3 ounces concentrated hydrochloric acid and dissolve in this 6 pounds of dry zinc chloride powder, adding this to 7 pints of denatured alcohol. The same method of preparation is used as for the 53 per cent solution. This strength of solution can also be prepared by diluting the 53 per cent solution at the rate of 1 gallon to 3 pints of denatured alcohol. Formula for 33 per cent solution To 2 pints hot water add 3 ounces concentrated hydrochloric acid and dissolve in this 4 x /2 pounds of dry zinc chloride powder, adding this to 7 pints of denatured alcohol. The same method of preparation is used as for the 53 per cent solution. This strength of solution can also be prepared by diluting the 53 per cent solution, at the rate of 1 pint to 1 pint of denatured alcohol, or by diluting the 43 per cent solution at the rate of 2 pints to 1 pint of denatured alcohol. In dissolving zinc chloride, stir thoroughly while hot and crush all hard lumps with a wooden paddle. Cool as rapidly as possible, covering with a lid to prevent evaporation. Keep in large bottles or cans, well stoppered. If much of the alcohol evaporates the strength of the solution is increased. While using in the field only enough should be taken out in the open jar to last a few hours at a time. Sediments consist of impurities. It is not necessary to stir the solu- tion before using because the sediments are not useful. Keep the dry zinc chloride powder well sealed for it absorbs moisture very rapidly. To distinguish the solutions in the field without stopping to read the labels the 43 per cent can be colored with a few drops of laundry bluing and the others can be distinguished by the fact that the 53 per cent is somewhat syrupy. Also different sizes of jars with different 10 California Agricultural Extension Service [Gntc. 45 sizes of brushes can be used. For example, use a 2-inch brush for the 53 per cent, a lV^-inch brush for the 43 per cent, and a 1%-inch brush for the 33 per cent. STRENGTH OF ZINC CHLORIDE TO USE The penetration of zinc chloride into bark varies with varieties, age of trees, temperature, soil conditions, climate, etc. But the grower should begin with the strengths of solutions recommended for the various sizes of branches, and then make changes if experience seems to warrant. For instance, if too many cankers fail to stop he can conclude that a stronger solution should have been used. Also, if too many branches die, then perhaps the solution was too strong for that size of branch at that time of year, providing that the cankers on the dead branches were not too old when they were treated. In interior sections of California the solutions penetrate much more freely after the hot summer weather begins, sometime in June. Also very high temperatures sometimes seem to "scald" the treated bark, on smooth-barked branches, even if the high temperature occurs some weeks after the application. This occurs particularly on branches exposed to the direct rays of the sun. Along the coast the temperature perhaps has less influence — though there has not been enough expe- rience in treating blight in coast districts from which to draw accu- rate conclusions. Cankers that have stopped running, on smooth-barked trunks and branches, can be treated with a solution weaker than would be neces- sary for an active canker, on the same size of branch. Such cankers if not treated will continue to penetrate inwardly and kill the cam- bium layer and also many would later awaken and run downward into the trunks and roots. The following table has been prepared to give, as definitely as possible, the available information upon this point. From the nature of the subject, however, it is impossible to give specific directions which will fit all cases. Strength of Solution to Use Under Varying Conditions Orchards over 20 years of age 53% on all branches and trunks at all times of year. 43% on roots over 2% inches in diameter. 33% on roots under 2% inches in diameter. 1930] z INC Chloride Treatment for Pear Blight Cankers 11 Orchards 6 to 20 years of age Before and after hot weather 53% on trunks. 53% on all scaly-barked branches. 53% on smooth-barked branches over 2 inches in diameter. 43% on smooth-barked branches under 2 inches in diameter. 43% on roots over 2% inches in diameter. 33% on roots under 2y 2 inches in diameter. During hot weather 53% on all scaly-barked branches. 53% on trunks over 7 years, or younger if scaly bark has developed. 53% on smooth-barked branches over 4 inches in diameter. 43% on smooth-barked branches 2% to 4 inches in diameter. 33% on branches under 2% inches in diameter. 43% on roots over 3 inches in diameter. 33% on roots under 3 inches in diameter. Orchards 2 to 5 years of age Before and after hot weather 43% on trunks 4 to 5 years; or 53% on 5-year trees, if exceptionally large. 33% on trunks 2 to 3 years old; or 43% on 3-year trees, if exceptionally large. 43% on branches over 1*4 inches in diameter. 33% on branches under iy 2 inches in diameter. 33% on roots. During hot weather 43% on trunks of 5-year trees, if exceptionally large. 33% on trunks of trees 2 to 5 years of age. 33% on branches of all sizes. 33% on roots. When in doubt as to which solution to use on a branch, use the stronger solution, for it is better to kill the branch than not to stop the disease. In old orchards - (over 20 years of age) the strongest solution (53 per cent) is used on all sizes of branches. At times this may over- penetrate and kill young, thin-barked branches, under 1% inches in diameter in old trees. But loss from that cause is over-balanced by failure to stop some cases of blight with weaker solutions ; for the bark is often rather thick even on small branches in old trees. If sufficient experienced help is available a 43 per cent solution can be used to advantage in saving thin-barked branches in old orchards. The weaker solutions should not be used on scaly-barked branches, no matter how small. In treating scaly-barked trunks and branches a higher per- centage of cure is obtained if the loose scales are scraped off before applying the 53 per cent solution. In so doing avoid as much as 12 California Agricultural Extension Service [Cerc. 45 possible exposing" live, white bark beneath. Saturate scaly bark thoroughly with the solution. In treating cankers on trees fifty or sixty years of age, it is necessary to shave the thick, dead, outer bark inwardly until streaks of live bark begin to appear. Streaks of blight often run downward a long distance in old cankers in these old trees. In younger orchards (6 to 20 years of age) 43 per cent solution is used in the spring time on branches under 2 inches in diameter. But after the hot weather begins, it is used on smooth-barked branches 2 x /2 to 4 inches in diameter, and 33 per cent is used on branches under 2% inches in diameter. During the summer the 53 per cent solution is used on trunks of trees over six or seven years of age and on scaly- barked branches of such trees. Even a scaly or corky condition in crotches of smooth-barked branches may prevent proper penetration of the weaker solutions unless care is taken to thoroughly saturate such places with the solution. In very young orchards (2 to 5 years of age), only the 33 and 43 per cent solutions are necessary. In this age of trees in the spring- time, 33 per cent is used on branches under 1% inches in diameter and 43 per cent on larger branches and trunks. After hot weather begins the 33 per cent is used exclusively on these trees. On trunks of trees 2 to 3 years of age use 33 per cent solution at all times of the year. On trunks of trees 4 to 5 years of age use 43 per cent in the spring and 33 per cent in the summer. On trunks of trees 6 years of age and over use 53 per cent during the spring, but in summer reduce to 43 per cent on trunks of trees 6 to 7 years of age unless considerable scaly bark has developed. A tree under 10 or 12 years of age in which the root crown has greatly outgrown the trunk is apt to be overpenetrated by the zinc chloride at that point. In such cases excess solution at the root crown should be mopped up with a wet cloth. The graft or bud union of young trees is more readily injured by zinc chloride than are other parts of the trunk and root-crown. Whether the blight penetrates more deeply at that point has not been determined. This injury is especially common when the solution is applied from the root-crown and up the trunk to, or above, the crotches. In these long cankers the zinc chloride solution creeps down- ward and thus increases the concentration at the root-crown. Treat- ments at the root-crown which extend only a short distance up the trunk seldom overpenetrate the graft union unless the blight canker was old at the time of treatment. 1930] Zinc Chloride Treatment for Pear Blight Cankers 13 In treating root cases use 43 per cent on all roots over 2% or 3 inches in diameter, and 33 per cent solution on roots smaller than this. If the solution runs down into the soil the saturated soil should be removed as soon as it has stopped running to prevent excessive penetration into the bark. During the summer exposed roots on young trees are often scalded by the sun so these should be protected by straw until after the zinc chloride has dried sufficiently to admit of covering with soil. Avoid as much as possible scarring the roots and crown with the shovel. METHOD OF APPLYING ZINC CHLORIDE In applying zinc chloride, lift the brush carefully from the solu- tion so that it will be dripping-full of the liquid. Paint from the top downward, with the handle pointed upward and the brush down- ward. It is better not to rub or scrub. Merely allow the solution to run freely over the bark so that it will creep into all the crevices and breathing pores. Also, rubbing soon ruins the brush. A dish mop is used by some operators, but the general tendency is not to apply enough solution when the dish mop is used. It is especially useful in the tops of trees since it does not drip the solution as freely as a brush. On larger branches the brush does much more rapid and thorough work. On trunks and lower parts of scaffold branches a two-ounce bulb syringe, throwing a solid stream, facilitates more rapid work. Avoid spattering the solution for it will burn fruit, leaves, and tender shoots. It is caustic to shoes and woolen clothing and painful to the eyes. Zinc chloride solution is very painful to the eyes and a large quan- tity accidentally spilled over the face might cause serious injury to the eyes. The solution irritates the skin of some persons more than others. It will burn the skin if the clothing becomes saturated and is allowed to remain in contact with the skin for some time. However, some operators have their fingers wet with the solution day after day without serious annoyance. Handled with care, it is not necessary to wear rubber gloves or goggles. A large wet towel should be used to wipe the solution off the skin. In case any considerable amount gets into the eyes wash them out with water and apply olive oil or salad oil, or whites of eggs. Cotton clothing is not greatly damaged by zinc chloride, but woolens, shoes, and leather gloves are. Rubber shoes and rubber gloves are not harmed. If any special problems arise in connection with pear blight that are not covered in this publication, the grower should consult the county farm advisor. AGRICULTURAL EXTENSION SERVICE CIRCULARS No. 1. 2. 3. 4. 5. 9. 10. 11. 13. 14. 15. 16. No. Series on Califorina Crops and Prices: 17. Peaches. Home Preparation of Jelly and Marma- 19. lade. 20. Feeding Beef Cattle in California. 21. Irrigation by Overhead Sprinkling. 22. Series on California Crops and Prices: 23. Lettuce. 24. Care and Management of the Milk Goat. Suggestions on Grapefruit Culture in 25. Imperial Valley. 26. Diseases and Parasites of Poultry in 29. California. Rabbit Raising. 30. The Home Preparation of Fruit Candy. Cauliflower Production. 31. The Manufacture of Monterey Cheese. Selection and Care of Electrical Equip- 32. ment Used in Dairy Manufacturing. 33. Pork Production in California. Irrigation of Orchards by Contour Fur- 34. rows. 35. Liver Fluke and Stomach Worm of Sheep. Artificial Incubation of Eggs. Pear Blight Control in California. Bovine Tuberculosis. Thinning Sugar Beets. Strawberry Culture in California. Enterprise Efficiency Studies on Cali- fornia Farms. Bush Fruit Culture in California. The Home Vegetable Garden. Control of Pocket Gophers and Moles in California. Elements of Grape Growing in Cali- fornia. Powdery Mildew of the Grape and Its Control in California. What to Do About Bovine Tuberculosis. Rearing Dairy Heifers free from Tuber- culosis and Abortion Diseases. Plum Growing in California. Alfalfa Production. STATION PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION BULLETINS No. 253. Irrigation and Soil Conditions in the Sierra Nevada Foothills, California. 263. Size Grades for Ripe Olives. 277. Sudan Grass. 279. Irrigation of Rice in California. 283. The Olive Insects of California. 304. A Study of the Effects of Freezes on Citrus in California. 310. Plum Pollination. 313. Pruning Young Deciduous Fruit Trees. 331. Phylloxera-resistant stocks. 335. Cocoanut Meal as a Feed for Dairy Cows and Other Livestock. 343. Cheese Pests and Their Control. 344. Cold Storage as an Aid to the Market- ing of Plums, a Progress Report. 346. Almond Pollination. 347. The Control of Red Spiders in Decid- uous Orchards. 348. Pruning Young Olive Trees. 349. A Study of Sidedrai't and Tractor Hitches. 353. Bovine Infectious Abortion, and Asso- ciated Diseases of Cattle and New- born Calves. 354. Results of Rice Experiments in 1922. 357. A Self-Mixing Dusting Machine for Applying Dry Insecticides and Fun- gicides. 361. Preliminary Yield Tables for Second- Growth Redwood. 362. Dust and the Tractor Engine 363. The Pruning of Citrus Trees in Cali- fornia. 364. Fungicidal Dusts for the Control of Bunt. 366. Turkish Tobacco Culture, Curing, and Marketing. 367. Methods of Harvesting and Irrigation in Relation to Moldy Walnuts. 368. Bacterial Decomposition of Olives During Pickling. 369. Comparison of Woods for Butter Boxes. 370. Factors Influencing: the Development of Internal Browning of the Yellow Newtown Apple. 371. The Relative Cost of Yarding Small and Large Timber. 373. Pear Pollination. 374. A Survey of Orchard Practices in the Citrus Industry of Southern Cali- fornia. 380. Growth of Eucalyptus in California Plantations. 385. Pollination of the Sweet Cherry. 386. Pruning Bearing Deciduous Fruit Trees. 388. The Principles and Practice of Sun- Drying Fruit. 389. Berseem or Egyptian Clover. 390. Harvesting and Packing Grapes in California. 391. Machines for Coating Seed Wheat with Copper Carbonate Dust. 392. Fruit Juice Concentrates. 393. Crop Sequences at Davis. 394. I. Cereal Hay Production in California. II. Feeding Trials with Cereal Hays. 395. Bark Diseases of Citrus Trees in Cali- fornia. 396. The Mat Bean, Phaseolus Aconitifolius. 397. Manufacture of Roquefort Type Cheese from Goat's Milk. 400. The Utilization of Surplus Plums. 405. Citrus Culture in Central California. 406. Stationary Spray Plants in California. 407. Yield, Stand, and Volume Tables for White Fir in the California Pine Region. No. 408. Alternaria Rot of Lemons. 409. The Digestibility of Certain Fruit By- products as Determined for Rumi- nants. Part I. Dried Orange Pulp and Raisin Pulp. 410. Factors Influencing the Quality of Fresh Asparagus After it is Harvested. 412. A Study of the Relative Value of Cer- tain Root Crops and Salmon Oil as Sources of Vitamin A for Poultry. 414. Planting and Thinning Distances for Deciduous Fruit Trees. 415. The Tractor on California Farms. 416. Culture of the Oriental Persimmon in California. 418. A Study of Various Rations for Fin- ishing Range Calves as Baby Beeves. 419. Economic Aspects of the Cantaloupe Industry. 420. Rice and Rice By-Products as Feeds for Fattening Swine. 421. Beef Cattle Feeding Trials, 1921-24. 423. Apricots (Series on California Crops and Prices). 425. Apple Growing in California. 426. Apple Pollination Studies in California. 427. The Value of Orange Pulp for Milk Production. 428. The Relation of Maturity of California Plums to Shipping and Dessert Quality. 430. Range Grasses in California. 431. Raisin By-Products and Bean Screen- ings as Feeds for Fattening Lambs. 432. Some Economic Problems Involved in the Pooling of Fruit. 433. Power Requirements of Electrically Driven Dairy Manufacturing Equip- ment. 434. Investigations on the Use of Fruits in Ice Cream and Ices. 435. The Problem of Securing Closer Rela- tionship between Agricultural Devel- opment and Irrigation Construction. 436. I. The Kadota Fig. II. The Kadota Fig Products. 438. Grafting Affinities with Special Refer- ence to Plums. 439. The Digestibility of Certain Fruit By- Products as Determined for Rumi- nants. II. Dried Pineapple Pulp, Dried Lemon Pulp, and Dried Olive Pulp. 440. The Feeding Value of Raisins and Dairy By-Products for Growing and Fattening Swine. 444. Series on California Crops and Prices: Beans. 445. Economic Aspects of the Apple In- dustry. 446. The Asparagus Industry in California. 447. A Method of Determining the Clean Weights of Individual Fleeces of Wool. 448. Farmers' Purchase Agreement for Deep Well Pumps. 449. Economic Aspects of the Watermelon Industry. 450. Irrigation Investigations with Field Crops at Davis, and at Delhi, Cali- fornia, 1909-1925. 451. Studies Preliminary to the Establish- ment of a Series of Fertilizer Trials in a Bearing Citrus Grove. 452. Economic Aspects of the Pear Industry. 453. Series on California Crops and Prices: Almonds. 454. Rice Experiments in Sacramento Val- ley, 1922-1927. BULLETINS— (Continued) No. No. 455. Reclamation of the Fresno Type of 465. Black-Alkali Soil. 466. 456. Yield. Stand and Volume Tables for Red Fir in California. 467. 458. Factors Influencing Percentage Calf 468. Crop in Range Herds. 459. Economic Aspects of the Fresh Plum 469. Industry. 470. 460. Series on California Crops and Prices: Lemons. 471. 461. Series on California Crops and Prices: Economic Aspects of the Beef Cattle 474. Industry. 462. Prune Supply and Price Situation. 464. Drainage in the Sacramento Valley 475. Rice Fields. Curly Top Symptoms of the Sugar Beet. The Continuous Can Washer for Dairy Plants. Oat Varieties in California. Sterilization of Dairy Utensils with Humidified Hot Air. The Solar Heater. Maturity Standards for Harvesting Bartlett Pears for Eastern Shipment. The Use of Sulfur Dioxide in Shipping Grapes. Factors Affecting the Cost of Tractor Logging in the California Pine Region. Walnut Supply and Price Situation. CIRCULARS No. 115. Grafting Vinifera Vineyards. 117. The Selection and Cost of a Small Pumping Plant. 127. House Fumigation. 129. The Control of Citrus Insects. 164. Small Fruit Culture in California. 166. The County Farm Bureau. 178. The Packing of Apples in California. 203. Peat as a Manure Substitute. 212. Salvaging Rain-Damaged Prunes. 230. Testing Milk. Cream, and Skim Mi]l< for Butterfat. 232. Harvesting and Handling California Cherries for Eastern Shipment. 239. Harvesting and Handling Apricots and Plums for Eastern Shipment. 240. Harvesting and Handling California Pears for Eastern Shipment. 241. Harvesting and Handling California Peaches for Eastern Shipment. 243. Marmalade Juice and Jelly Juice from Citrus Fruits. 244. Central Wire Bracing for Fruit Trees. 245. Vine Pruning Systems. 248. Some Common Errors in Vine Pruning and Their Remedies. 249. Replacing Missing Vines. 250. Measurement of Irrigation Water on the Farm. 253. Vineyard Plans. 255. Leguminous Plants as Organic Ferti- lizers in California Agriculture. 257. The Small-Seeded Horse Bean (Vicia faba var. minor). 258. Thinning Deciduous Fruits. 259. Pear By-Products. 261. Sewing Grain Sacks. 262. Cabbage Production in California. 263. Tomato Production in California. 265. Plant Disease and Pest Control. 266. Analyzing the Citrus Orchard by Means of Simple Tree Records. No. 269. 270. 276. 277. 278. 279 282. 284. 287. 288. 289. 290. 292. 294. 295. 296. 298. 300. 301. 302. 304. 305. 307. 308. 309. 310. 311. 312. 313. 314. 315. An Orchard Brush Burner. A Farm Septic Tank. Home Canning. Head, Cane, and Cordon Pruning of Vines. Olive Pickling in Mediterranean Countries. The Preparation and Refining of Olive Oil in Southern Europe. Prevention of Insect Attack on Stored Grain. The Almond in California. Potato Production in California. Phylloxera Resistant Vineyards. Oak Fungus in Orchard Trees. The Tangier Pea. Alkali Soils. Propagation of Deciduous Fruits. Growing Head Lettuce in California. Control of the California Ground Squirrel. Possibilities and Limitations of Coop- erative Marketing. Coccidiosis of Chickens. Buckeye Poisoning of the Honey Bee. The Sugar Beet in California. Drainage on the Farm. Liming the Soil. American Foulbrood and Its Control. Cantaloupe Production in California. Fruit Tree and Orchard Judging. The Operation of the Bacteriological Laboratory for Dairy Plants. The Improvement of Quality in Figs. Principles Governing the Choice, Oper- ation and Care of Small Irrigation Pumping Plants. Fruit Juices and Fruit Juice Beverages. Termites and Termite Damage. The Mediterranean and Other Fruit Flies. 15m-6,'30