UNIVERSITY OF CALIFORNIA PUBLICATIONS COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT BY WILLIAM W. MACKIE and FRED N. BR1GGS (Based on investigations conducted under cooperative agreement, between the Office of Cereal Investigations, of the Bureau of Plant Industry, United States Department of Agriculture, and the Univer sity of California Agricultural Experiment Station.) BULLETIN No. 364 Berkeley, California, May, 1923 UNIVERSITY OF CALIFORNIA PRESS BERKELEY 1923 David P. Barrows, President of the University. EXPERIMENT STATION STAFF HEADS OF DIVISIONS Thomas Forsyth Hunt, Dean. Edward J. Wickson, Horticulture (Emeritus). , Director of Eesident Instruction. C. M. Haring, Veterinary Science, Director of Agricultural Experiment Station. B. H. Crocheron, Director of Agricultural Extension. C. B. Hutchison, Plant Breeding, Director of the Branch of the College of Agriculture at Davis. H. J. Webber, Sub-tropical Horticulture, Director of Citrus Experiment Station. William A. Setchell, Botany. Myer E. Jaffa, Nutrition. Ralph E. Smith, Plant Pathology. John W. Gilmore, Agronomy. Charles F. Shaw, Soil Technology. John W. Gregg, Landscape Gardening and Floriculture. Frederic T. Bioletti, Viticulture and Fruit Products. Warren "T. Clarke, Agricultural Extension. Ernest B. Babcock, Genetics. Gordon H. True, Animal Husbandry. Walter Mulford, Forestry. James T. Barrett, Plant Pathology. W. P. Kelley, Agricultural Chemistry. H. J. Quayle, Entomology Elwood Mead, Rural Institutions. H. S. Reed, Plant Physiology. L. D. Batchelor, Orchard Management. W. L. Howard, Pomology. "Frank Adams, Irrigation Investigations. C. L. Roadhouse, Dairy Industry. R. L. Adams, Farm Management. W. B. Herms, Entomology and Parasitology. John E. Dougherty, Poultry Husbandry. D. R. Hoagland, Plant Nutrition. G. H. Hart, Veterinary Science. L. J. Fletcher, Agricultural Engineering. Edwin C. Voorhies, Assistant to the Dean. DIVISION OF AGRONOMY J. W. Gilmore B. A. Madson P. B. Kennedy J. F. Duggar G. W. Hendry J. P. Conrad W. W. Mackie * la cooperation with Division of Agricultural Engineering, Bureau of Public Roads, U. 8. Department of Agriculture. FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT By WILLIAM W. MACKIE and FRED N. BRIGGS CONTENTS PAGE Fungicidal dusts for the control of bunt or stinking smut of wheat 533 Early experiments with chemical dusts for the control of bunt 536 Plan of procedure 537 Influence of spore load upon bunt attack 539 Control of bunt by solutions of standard fungicides 540 Effect of flowers of sulfur on bunt control 540 Control of bunt by copper sulfate powder 543 Copper sulfate dust as a substitute for copper corbonate 545 Miscellaneous chemical dusts 545 Effect of copper carbonate dust on control of bunt 545 Effect of dilution of copper carbonate on bunt control 548 Comparative effectiveness of some commercial samples of copper carbonate 549 Effect of fungicidal dusts upon seed germination 551 Stimulation of wheat seedlings by copper carbonate dust 553 Standards of chemical purity and physical fineness for copper carbonate dust 554 Suggested qualities for a standard copper carbonate 557 Machines for applying copper carbonate dust 560 Effect of copper carbonate dust upon operators 563 Demonstrations with copper carbonate dust on farms 563 Sources of copper carbonate 566 Summary 567 FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT OR STINKING SMUT OF WHEAT Bunt, or stinking smut, has long been recognized as a destructive disease of wheat. Its control, however, was not undertaken in a scientific or effective manner until about the middle of the last century, when Kuhn 18 began his classic experiments on the effect of copper sulfate on the spores of the bunt fungus. Although effective remedies for control of bunt have been found in the use of bluestone (copper sulfate and formaldehyde), their universal application has not been practiced for the following reasons: 1. Bluestone solutions of sufficient strength to destroy the bunt spores kills the wheat germ, or so affects it that the growth of the primary roots are delayed or the plumule is distorted and weakened. 534 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Forty to 60 per cent of the wheat treated by bluestone on our Cali- fornia farms never comes up. Solutions which do not injure the germ are too weak to prevent bunt infection. 2. The dipping of bluestone-treated wheat in a lime solution pre- vents the greater portion of the bluestone injury, but has the dis- Fig. 1. — No. 5, bunted White Australian head and bunt gall. No. 6, normal White Australian head and kernel. Natural size. Under competitive field con- ditions bunt attack reduces the size of the plant, head and kernel. advantages of extra cost in labor and time. The additional costs could be borne if this were all, but frequently heavy losses of seed treated by the bluestone-lime method have occurred when such seed has been stored too wet. When seed is properly dried, as usually is the case with seed treated early in the fall before the rainy season BULLETIN 364] FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT 535 is far advanced, no injury from heating or fermentation occurs. But when weather conditions force the farmer to store seed too wet, the lime coating prevents proper drying, and seed losses may follow. 3. Formaldehyde is an effective remedy against infection from seed-borne spores of the bunt fungus and several other smuts of cereals, but it, too, is limited by its destruction of seed germs under certain climatic conditions, as has been conclusively shown by investi- ng. 2. — Eoot development retarded by bluestone. Normal seedling to left. Seedlings with delayed root development frequently die. In others, delayed growth and maturity result. gations in California. 17 ' 21 The experience of farmers in California and other semi-arid regions 6 positively shows that seed injury results from formaldehyde-treated seed either when stored dry for a period of more than 48 hours before seeding or when seeded into soil too dry to cause immediate germination. This injury is seen in destroyed germs, distorted plumules, and weakened seedlings. Instances have been recorded in California where thousands of acres sown with 536 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION formaldehyde-treated seed failed to produce even a poor stand. Owing; to the necessity of California farmers having to sow much of their summer fallowed lands before the rainy season begins, formaldehyde cannot be used without liability to severe seed injury. 4. The loss of time at the busy seeding period tends to prevent seed treatment. It has been shown by von Tubeuf 29 that seed from a crop with only one or two per cent of bunt showing no visible spores may in the following crop produce 20 to 30 per cent of smutted plants. Seed treatment, therefore, should be practiced every year whether bunt appears to be present or not. In order to induce the farmer to treat his seed wheat for bunt every year, the difficulties presented in the use of solutions of blue- stone, bluestone and lime, and formaldehyde, must be obviated. An effective fungicide, which can be applied to seed long in advance of seeding operations, and which will not injure seed germs even in the hands of careless farm help, must be provided if universal con- trol of bunt is to be attained. The copper carbonate dust method of seed treatment appears to meet these requirements. The results of three years' experiments and tests to determine the effectiveness as well as the limitations of copper carbonate dust when applied to bunt-infested seed are here presented in support of this new method of seed treatment. EARLY EXPERIMENTS WITH CHEMICAL DUSTS FOR THE CONTROL OF BUNT Farmers always have desired a dry fungicide because of the difficulties and costs connected with the use of liquid preventives. Lime, either burnt or air-slaked, has long been applied as a powder, but ineffective control of bunt has prevented its acceptance. Bolley 3 tried many dry processes, testing among others "dry powdered formaldehyde mixed with chloride of lime and flowers of sulfur, and suggests that extended research might develop a satisfactory dry method. His own experiment gave little or no bunt control, and much seed injury. Copper carbonate dust as a smut fungicide was used by von Tubeuf in 1902, 29 who treated heavily bunted seed with copper car- bonate dust and secured only 1.7 per cent of bunted heads. At the same time untreated seed gave 29.3 per cent, while Bordeaux powder gave 14.9 per cent. No reason is given why the use of copper car- bonate dust was not continued. Darnell-Smith 7 ' 8 > 9 > ai experimented BULLETIN 364] FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT 537 with heavily bunt-infected seed at Cowra and at Wagga in New South Wales in 1915 and later. He secured better results in bunt control and seed germination with copper carbonate dust (2 ounces per bushel) than with standard methods. Following the success of Darnell-Smith, preliminary experiments with copper carbonate dust were made at Berkeley and Davis 22 - 23 in 1920. These experiments were highly encouraging, but were limited owing to late seeding (March 8 and April 9). During the years 1921 and 1922, a large number of experiments were conducted at Davis. Care was taken to check, with many duplications, all dust treatments with the standard bluestone and formaldehyde treatments. Because of the large number of experiments conducted, it has been found necessary to present these results in averages. PLAN OF PROCEDURE A method of seed treatment so new, and presenting so many obvious practical advantages if successful, must of necessity be tried out under the most rigid tests. The following methods, therefore, were followed in the two years' trials at Davis. 1. The bunt spores were grown during the preceding year and consisted only of spores of Tilletia tritici (Bjerk.) Wint. 2. As previous experiments had been rendered inconclusive by irregular smut infection, a graduated scale of bunt spore dosage was used. Before the seed was treated with the fungicide, each lot was dosed with a given weight of bunt spores to a given weight of wheat seed, as follows: Grades Bunt Spores in Grams Wheat Seed in Grams 1 1 30 2 1 250 3 1 500 4 1 750 5 1 1000 6 1 1500 7 1 2000 8 1 2500 9 1 3000 3. Little Club wheat, highly susceptible to bunt (pi. 3), but very resistant to lodging and shattering, was used in 1921. Because of its late maturity and susceptibility to stem rust, it was replaced in 1922 by White Federation, an equally bunt-susceptible but much earlier variety and fairly resistant to lodging and shattering. 538 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 4. The quantity of chemical dusts applied to the seed was grad- uated into four rates, except flowers of sulfur, for which greater quantities were used. 5. The plots were arranged in rows separated by a space of one foot. The seed was accurately weighed so as to give 150 ± 2 kernels per rod row. Fig. 3. — No. 1, bunted Little Club and bunt gall (natural size). No. 2, normal Little Club bead and kernel. Bunted Club wheat shows reduced thickness of head. 6. Because both plants as well as heads were to be counted, the seeds were dropped by hand and spaced at an average distance of 1% inches. As approximately 50 per cent of the seed fails to produce plants in the soil at Davis, the harvested plants were separated on the average by more than 2y 2 inches, thus making possible an accurate separation of the plants at harvest time. To prevent breaking of plants, the soil was softened by irrigation previous to pulling. BULLETIN 364] FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT 539 INFLUENCE OF SPORE LOAD UPON BUNT ATTACK Field observations supported by counts of bunt spores on seed wheat indicate that the number of spores per kernel decidedly in- fluence the bunt attack. Seed carrying no more than ten spores on each kernel has not been observed to give infection. The seed for the 1921 crop was separated into nine lots, according to the quantity of bunt spores applied. The dosage by weight ranged from 1 part of bunt spores to 30 parts of seed wheat (1-30) to 1 to 3000 parts (1-3000). This last, or lightest dosage, yielded several hundred bunt spores per kernel (pis. 1 and 2). The effect of variation in the dosage of bunt spores on seed is shown in table 1. TABLE 1 Summary of Bunt Attack According to the Dosage of Spores. Experiments Conducted During 1921 and 1922 at Davis Per Cent of Bunt by Head Count Spore Dosage to Seed by Weight 1-30 Bunt 1-250 Bunt 1-500 Bunt 1-750 Bunt 1-1000 Bunt 1-1500 Bunt 1-2000 Bunt 1-2500 Bunt 1-3000 Bunt per cent per| cent perl cent per cent per cent per cent per cent per cent • per cent Average 1921 61.6 37.3 37.0 28.7 20.7 ■ 16.3 16.1 10.6 10.3 Average 1922 36.8 41.4 45.5 39.6 25.7 31.9 21.0 These results show that the bunt attack is reduced as the dosage is decreased. The influence of spore dosage upon the effectiveness of various chemicals is very marked and conforms generally to the scale of bunt reduction shown in table 1. The scale of spore dosage is therefore conducted as an essential part of every set of experiments with fungicidal solutions or dusts. Those results agree closely with those secured by Heald, at Pullman, Washington, 15 whose researches caused him to believe that an accurate prediction of the possible bunt per cent in a crop can be made from determination of the number of spores on the seed sown. 540 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION CONTEOL OF BUNT BY SOLUTIONS OF STANDARD FUNGICIDES Standard solutions previously proven effective in preventing infection from seed-borne spores were used as checks for comparison wherever fungicides in the dust or powder form were being tested. TABLE 2 Relative Effectiveness of Standard Fungicidal Solutions in Preventing Bunt Infection Under Varying Dosages of Spores in Experiments Conducted at Davis Per Cent of Bunt by Head Count Treatment Check (Untreated) Bluestone (1-5) 3" Bluestone (1-4) 3" + Lime d-8)5" Formaldehyde (1-40) 10" .... Spore Dosage to Seed by Weight 1-30 Per Cent Bunt 49.2 2.5 .7 1.1 1-250 Per Cent Bunt 1.2 1-500 Per Cent Bunt 41.2 .4 .6 .2 1-750 Per Cent Bunt 34.1 1-1000 Per Cent Bunt 23.2 .3 .1 0.0 1-1500 Per Cent Bunt 24.1 0.0 .1 .1 1-2000 Per Cent Bunt 18.5 .1 .1 .1 1-2500 Per Cent Bunt 10.6 0.0 .1 .1 1-3000 Per Cent Bunt 10.3 0.0 0.0 .2 All three of the standard fungicidal solutions are shown to be practically completely effective when properly applied even for the very heaviest dosage of bunt spores used in these experiments. It remains, therefore, to compare the effectiveness of fungicidal dusts and powders with the fungicidal solutions. EFFECT OF FLOWERS OF SULFUR ON THE CONTROL OF BUNT Farmers from time to time have reported successful control of bunt by means of flowers of sulfur. To test the efficacy of this dust, exhaustive experiments were conducted at Davis in 1919, 1920 and 1921. The experiments in 1919 indicated that sulfur was not fully effective against infection when the seed was blackened with bunt. The experiments in 1920 showed that sulfur and seed wheat mixed and drilled at the rate of 25 pounds of flowers of sulfur to 100 pounds of seed reduced bunt to one-tenth (61.8 per cent to 6.3 per cent), but in no case eliminated it. Sulfur produced no effect in preventing infection from spores already in the soil. In order finally to determine the limitations of flowers of sulfur as a bunt fungicide, 135 tests with this dust were made at Davis in 1921. The usual rod-row method was employed. The dosage of bunt BULLETIN 364] FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT 541 spores applied to the seed was arranged in nine lots, varying from 1-30 to 1-3000 by weight. The results of these duplicate experiments are summarized in table 3. TABLE 3 Effectiveness of Flowers of Sulfur in Preventing Bunt Infection Under Varying Dosages of Spores in Experiments Conducted During 1921 at Davis Per Cent of Bunt by Head Count Treatment Check (Untreated) Dipped Bluestone (1-5) 3" .. Dipped bluestone (1-4) 8"; limed (1-8) 5"...., Dipped formaldehjyde (1-40) 10" Sulfured 25 lbs. per 100 lbs. seed Sulfured 15 lbs. per 100 lbs. seed Sulfured 5 lbs. per 100 lbs. seed Sulfured 2 lbs. per 100 lbs. seed Sulfured 1 lb. per 100 lbs. seed Sulfured Y 2 lb. per 100 lbs. seed Sulfured \i lb. per 100 lbs. seed Spore Dosage to Seed by Weight 1-30 Per Cent Bunt 61.5 .9 .2 2.4 32.6 43.5 37.0 49.9 48.6 56.8 65.4 1-250 Per Cent Bunt 47.3 1.5 .1 3.0 7.2 5.6 18.1 28.0 44.0 35.4 51.9 1-500 Per Cent Bunt 51.3 .6 0.0 .2 5.2 9.3 19.0 20.3 28.0 32.1 34.6 1-750 Per Cent Bunt 35.4 .3 0.0 0.0 6.9 6.2 10.5 14.2 21.6 22.6 18.4 1-1000 Per Cent Bunt 31.6 .3 .4 0.0 4.0 4.2 9.5 14.4 17.5 17.0 20.4 1-1500 Per Cent Bunt 26.5 0.0 0.0 0.0 2.5 4.8 5.2 7.4 16.4 11.7 16.5 1-2000 Per Cent Bunt 21.6 0.0 0.0 0.0 .6 2.2 4.0 7.1 6.8 7.2 7.9 1-2500 Per Cent Bunt 21.3 0.0 0.0 0.0 .1 .5 3.8 .2 4.2 7.0 5.2 1-3000 Per Cent Bunt 10.9 0.0 0.0 0.0 .1 1.0 .6 2.6 2.6 4.4 8.7 The evidence of these experiments with sulfur indicate: (1) that flowers of sulfur sown with seed at rates varying from % to 25 pounds of sulfur per 100 pounds of seed, reduces seed-borne infection but does not wholly prevent it; (2) as the quantity of sulfur is increased from 14 pound to 25 pounds per 100 pounds of seed, the bunt attack is correspondingly reduced, but even the 25 pound rate does not entirely prevent infection; and (3) because of these limitations flowers of sulfur cannot be recommended as a practical remedy for bunt control. 542 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Ml o *}&$& 9 >-"£"£ Igll g ^ ■"1 o H rrj § 1 § -° n ft g pq Ph ' a; H. 'Offl ' 6 3 'Offl _L Ph r > rr. qoio o o O . a o a> . «H N^ N^ Ny-, h I (N I CO U I i?i?i?T? 5?, ©©© HCOiONOCO-^cO IT. ©©© lOffiHOlNN "tf HH(MCO.t COCOCC iO Hiio iO iO "O »o iO A © i-H C NiQHOOOOOO X © t^ oc (NCONN^NHiO X co t^oc ©©OS©©©©© 3 .o ,5 M M E3 rQ 3 r, 00 ,0 ,0 0)^2 ^2 o hNhfthNhft ID O (D . CD G .. MfflCQIBtBWOQtC ~o;ajcviCpia;a>Ct)Cui rM ■■s P S £ Sppp^PPPS -|pqpQPt< a. | pq m pq pq pq pq pq pq U &Q Q Bulletin 364] FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT 543 CONTROL OF BUNT BY COPPER SULFATE POWDER Bluestone and bluestone-lime solutions for seed treatment are preferred on the Pacific Coast to formaldehyde because seed injury is generally less, and, in addition, bluestone has a residual repressive effect against infection from bunt-infested soils. It is natural, there- fore, that bluestone and bluestone-lime powder should be tested when dry treatments were considered. 22 The results of two years' experiments with bluestone powder are reported in table 4. Bluestone was prepared in various ways to test its effectiveness. First, powdered bluestone was shaken up with wheat at the rates of one, two, three, and four ounces per bushel of seed. As powdered bluestone is simply a mass of finely-divided crystals, the term powder is employed to differentiate it from copper carbonate dust, which is not crystalline, but amorphous. As bluestone powder appeared to be caustic to seed germs, 22 lime dust was added in sufficient quantities to react with the bluestone — usually two parts of bluestone to one part of lime, as is the case with the liquid bluestone-lime method of seed treatment. The increase in the amount of the bluestone powder from one to two ounces per bushel of seed in every case markedly increased its efficiency, but further increase to three and four ounces per bushel reduced the bunt attack little or not at all. It is evident, therefore, that two or three ounces per bushel are ample for the most effective control by this fungicidal powder. Because seed injury from bluestone dust was anticipated, lime dust (CaC0 3 ) was added in sufficient quantities to react chemically with the bluestone. The results show in every case that the addition of lime decreased the effectiveness of the bluestone by increasing the bunt attack from two to four times. As sound seed does not show any injurious effect from the bluestone powder for any of the doses from one to four ounces per bushel, there appears to be no necessity for adding the lime. One disadvantage of copper sulfate is its tendency to consolidate into masses, losing its powder form. This condition was thought to be due to the five molecules of water contained in bluestone (CuS0 4 .5H 2 0). Bluestone was heated to 103° C. and 206° C. respec- tively. Of the water of crystallization, only one molecule remained (CuS0 4 .H,0) at 103° C, and water-free anhydrous copper sulfate (CuSOJ was secured at 206° C. After months of exposure to air, these anhydrous copper sulfate powders still remained powdered and apparently unaltered. 544 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION TABLE 5 Use of Anhydrous Copper Sulfate in Preventing Bunt Infection Under a Dosage of Spores of 1 : 750 Experiments Conducted During 1922 at Davis Per Cent of Bunt by Head Count Treatment Germination Per Cent Lab. Field 99.8 68.0 49.3 35.0 92.0 36.6 99.6 48.2 98.0 51.0 100.0 54.3 99.0 55.0 98.0 48.0 100.0 53.3 98.0 54.6 Per Cent Bunt Check (untreated) Dipped bluestone (1-5) 3" Dipped bluestone (1-4) 3"; limed (1-8) 5" Dipped formaldehyde (1-40) 10" Dusted bluestone* — -2 oz Dusted bluestone* — 4 oz Dusted bluestone dehydrated f at 103° C. — 2 oz. Dusted bluestone dehydrated f at 103° C. — 4 oz. Dusted bluestone dehydrated f^at 206° C .— 2 oz. Dusted bluestone'dehydratedfat 206° C. — 4 oz. 28.6 0.0 0.0 0.0 6.6 1.2 .1 0.0 0.0 0.0 * Bluestone analyzed 98.27 per cent pure. t Bluestone (CuS0 4 .5H 2 0) dehydrated at 103° C. loses 4 molecules of water, becoming CuS0 4 .H 2 0. (CuS0 4 ) is secured. When dehydrated at 206° C, the pure anhydrous form The tests in table 5, made in duplicate, gave the following results for a bunt dosage of 1 to 750 : 1. The checks with the standard solutions of bluestone, bluestone- lime, and formaldehyde were practically completely effective (over 99 per cent). 2. Other experiments not here reported showed that the addition of salt (NaCl) or lime (CaC0 3 ) to the bluestone powders did not materially help its efficiency, but, on the contrary, lime sometimes reduced bunt control. Germination was not affected. 3. Bluestone, dehydrated at temperatures of 103° C. and 206° C, caused no material change in the effectiveness of the bluestone powder. 4. The results obtained with anhydrous copper sulfate indicate no improvement in the control of bunt or the prevention of seed injury. However, the anhydrous form remains in a pulverized con- dition much more certainly than powdered bluestone. BULLETIN 364] FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT 545 COPPER SULFATE DUST AS A SUBSTITUTE FOE COPPER CARBONATE As copper sulfate, or bluestone, is the basis for copper carbonate manufacture, there appears to be no reason why sufficient quantities of copper carbonate should not be manufactured. Malachite, a copper carbonate mineral occurring in the United States, was investigated, but it was found to be available in very limited quantities, and rather impure. Experiments demonstrated that malachite as a bunt preventive was greatly inferior to well- prepared copper carbonate dust. If, however, copper carbonate dust is not available in sufficient quantities, powdered bluestone may be used as a good substitute. Experiments conducted at Davis and in cooperation with farmers were successful, but the results were not as satisfactory as those in which copper carbonate dust was used. The greatest difficulty offered by bluestone lies in the fact that it is not easily reduced to a powder and in the further fact that it is difficult to maintain it in a loose powdered form sufficiently fine to adhere to seed. MISCELLANEOUS CHEMICAL DUSTS In addition to copper sulfate powder and copper carbonate dust, many other chemical powders and dusts were tested in an attempt to secure a common and relatively cheap fungicide. The list included malachite, paris green, barium carbonate, lead carbonate, ferrous sulfate, manganese dioxide, calcium carbonate, potassium sulfate, ammonium sulfate, sodium nitrate, superphosphate, sodium carbonate, sodium chloride, magnesium sulfate, and various combinations of lime and fungicides and of fertilizers. Some of them possess decided fungi- cidal properties, but all were far inferior to copper carbonate and copper sulfate in control of bunt. Seed injury occurred with paris green and superphosphate, but the addition of lime dust reduced or removed the injurious effects. EFFECT OF COPPER CARBONATE DUST ON THE CONTROL OF BUNT The accuracy of scientific experiments increases with the number of replications. The experiments with copper carbonate dust con- ducted for three years were repeated in duplicate in many series. During this period approximately 1,600,000 plants and 8,100,000 heads were individually examined, counted, and recorded. 546 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION m w M o 1-3000 Per Cent Bunt oo o q ©o o o lO 2 Ph m fe - o o us q q o o o 1— 1 CM CM • 1 • 1 1 1 KJ w o O w o § » s s t^ O O rH O rH cM O Oi-HOOOOOO O i— i o o o o oooooo T— 1 CM A H §^ N ffi O O O "* rH rH CM r- H O O O CM O O pa CO H K o a, OQ H Z pq CO h O O O CO OOO OO ea Q 2 1|H © N t^OOOOO OcOOOOOOO OS >0 ooooo o oooooo CM £ > O H o !?! 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C .aftftaaft CD CD O CD CD 21 and great reduction in germination. When such seed is sown in the field, poor stands result unless overcome by a very heavy increase in the rate of seeding. Farmers have reported sowing from 120 to 200 pounds of wheat per acre in an effort to overcome seed losses, a very considerable portion being due to seed treatment. As will be shown later, the soil itself takes a heavy toll of seed. When seed is dusted with copper carbonate it may be left in- definitely without fear of seed injury so far as the fungicide is concerned. 14 It even appears to have a somewhat repellent effect upon grain weevils. As copper carbonate dust does not attract moisture from the air, no reaction occurs until it comes in contact with the soil moisture. When there is sufficient soil moisture to start germination, moisture conditions are satisfactory for causing the copper carbonate to go into solution and become active. All treated seed sown in the plots was tested in the seed-testing laboratory of the United States Department of Agriculture.* At harvest time all plants were pulled and counted, and were then classified as bunted or clean. In this manner, a practical check on the survival of the seed sown in the soil was recorded. The germina- tion of seed under laboratory and field conditions are given in table 9. It is evident at once that the chemical solutions cause a great deal of injury to germination. On an average, only 31.4 per cent of the bluestoned seed survives in the soil, and but slightly more (39.6 per cent) under germination in the laboratory. The bluestone- lime dips show very favorable germination in the laboratory (73.6 per cent), but little more than half (53.8 per cent) as much when germinated in the soil. The lime bath following the bluestone solu- tion saves 26 per cent of the seed when compared with the bluestone alone. The formaldehyde under the favorable soil and moisture con- ditions at Davis gave as high germination in the soil as bluestone-lime. The chemical dusts, as a whole, cause practically no injury when compared with the untreated checks. Some depression appeared 552 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION when common salt (NaCl) was added to the bhiestone powder. To offset the depression caused by the salt, lime was added, with the result that the germination in soil was considerably superior to the untreated check plots. The addition of the lime, however, reduced the control of bunt. Copper carbonate dust in a large number of experiments gave somewhat better germination in the soil than the untreated seed. TABLE 9 Influence of Seed Treatment on the Per Cent of Germination of Seed Tested in the Laboratory at Berkeley and Seed Planted in the Field at Davis During 1921 and 1922 Fungicide and Treatment No. of tests Germination Per Cent *Lab. Field Check (Untreated) Solutions: Bluestone (1-5)3" Bluestone (1-4) 3"; limed (1-8) 5" Formaldehyde (1-40) 10" Dusts: Copper carbonate — 4 oz. to bu Bluestone — 4 oz. to bu Bluestone +lime (2-1) — 6 oz. to bu Bluestone dehydrated at 103° C — 4 oz. to bu.f Bluestone dehydrated at 206° C — 4 oz. to bu.... 1 part CuC0 3 to 3 parts gypsum — 4 oz. to bu... 1 part CuC0 3 to 1 part gypsum — 4 oz. to bu. .. 3 parts CuC0 3 to 1 part gypsum — 4 oz. to bu. . Sulfur: 25 lbs. per 100 lbs. seed 112 112 112 112 32 32 32 2 2 6 6 6 18 95.1 38.1 73.6 93.6 96.2 95.4 97.2 98.0 98.0 98.0 94.0 95.0 99.0 53.8 31.4 39.6 41.5 54.2 53.0 53.3 48.0 54.6 51.6 52.3 50.6 53.2 * We are indebted to Miss Etta Gilbert and Miss Grace Cole of the California Branch of the Seed Laboratory for germination tests. t Bluestone (CuS0 4 .5H 2 0) dehydrated at 103° C. loses 4 molecules of water, becoming CuS0 4 .H 2 0. When dehydrated at 206° C. the pure anhydrous form, CuS0 4 , is secured. The effect of the soil (Yolo silt loam) at Davis on seed germination was to reduce the natural air germination of seed wheat from 95.1 per cent to 53.8 per cent. Soils of a sandier texture would, of course, give better germination than those at Davis, but, on the other hand, harsher, heavier, poorly drained soils would give poorer germination and stands of grain. Undoubtedly the rate of seeding and consequent stand of grain is greatly influenced by the effect of soil texture on treated as well as untreated seed. PLATE 1 White Federation wheat. Dorsal side, X 30 diameters. Bunted at the rate of 1 part bunt spores to 3000 parts of seed. Approximately 1600 bunt spores per kernel. 15 As these are so few they are not visible to the naked eye and the seed passes as bunt free. PLATE 2 X 30 White Federation wheat. Ventral side, X 30 diameters. Bunted at the rate of 1 part of bunt spores to 3000 parts of seed. Approximately 1600 bunt spores per kernel. 15 As these are so few they are not visible to the naked eye and the seed pass as bunt free. PLATE 3 Little Club. Bunt free. Dorsal and ventral sides. X 30 diameters. The surface of seed wheat appears smooth to the naked eye, but the surface is here seen to be quite rough and capable of holding spores and copper carbonate dust readily. BULLETIN 364] FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT 553 STIMULATION OF WHEAT SEEDLINGS BY COPPEE CAEBONATE DUST Although the experiments conducted during 1920 22 - 23 were very limited in scope, they clearly indicated that no injury to germination resulted from treating seed wheat with copper carbonate. Germina- tion tests conducted in the laboratory at Berkeley and in the field at Davis in connection with a large number of experiments during Fig. 4. — Stimulation of wheat seedlings by copper carbonate dust. a. Effect of fungicidal dusts on wheat seedlings. Left to right: No. 1, un- treated seed; No. 2, bluestone dust applied at the rate of 4 ounces per bushel; No. 3, bluestone-lime dust mixed (2 to 1) and applied 6 ounces per bushel; No. 4, copper carbonate dust, 4 ounces per bushel. b. Effect of fungicidal solutions upon wheat seedlings: left to right: No. 5, untreated seed; No. 6, bluestone solution (1 lb. to 5 gals.), soaked 3 minutes; No. 7, bluestone dip (1 lb. to 4 gals.), soaked 5 minutes, followed by lime bath (1 lb. to 8 gals.), applied 5 minutes; No. 8, formaldehyde solution (1 pt. to 40 gals.), submerged 10 minutes. 1921 and 1922, show that seed treated with copper carbonate dust is equal to untreated seed and is superior to seed treated by the standard solutions. Seed treated with copper carbonate sprouted a few days earlier and grew more vigorously throughout the season than the others. Preliminary greenhouse experiments on wheat seedlings likewise indicate a decided stimulation following the use of copper carbonate. 554 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Numerous demonstrations on the use of copper carbonate treat- ments have been conducted throughout the state under the supervision of the farm advisors. All agree that no seed injury is evident where copper carbonate is used. Many report that seedlings from copper- carbonate treated seed emerge earlier and grow more vigorously than seedlings from untreated seed or from seed treated with the usual solutions. Others note no stimulation whatever. Reports from Washington 31 and Oregon 1 corroborate the observa- tions made in California on the absence of seed injury and apparent stimulation of seedlings by copper carbonate. STANDAEDS OF CHEMICAL PUKITY AND PHYSICAL FINENESS FOE COPPEE CAEBONATE DUST Commercial copper carbonate contains to a small extent various foreign ingredients due to the process of manufacture. The basis of manufacture consists of bluestone (CuS0 4 .5H 2 0), which usually contains a small quantity of iron, a survival in the manufacture of sulfuric acid from iron pyrites. Sodium carbonate is added to the copper sulfate solution, with the result that the copper carbonate is precipitated and the soluble sodium sulfate, a product of the reaction, is washed out, thus removing the sulfuric acid ion. When dried, the resultant powder is amorphous, entirely without crystals if pure, and greenish in color. Blue color indicates the presence of copper sulfate and an incomplete product. The chemical formula appears to be as follows: CuC0 3 .Cu(OH) 2 . The proportions of CuC0 3 and Cu(OH) 2 vary widely, according to the care exercised in its manu- facture. If too much heat is applied, carbon dioxide, added as sodium carbonate (Na 2 C0 3 ), is driven off as gas. This increases the propor- tion of copper hydrate at the expense of the copper carbonate. Still further heating decomposes the rather unstable copper hydrate, leaving as a result inert, dark brown copper oxide. The commercial product consists of a basic copper carbonate, amorphous in texture, very stable under ordinary conditions, and not subject to deliquescence or crystallization. Copper carbonate is listed as insoluble in pure water, but it is slowly soluble in dilute acids, such as carbonic, dicar- bonic, and undoubtedly many organic acids which normally occur in the soil. It is this quality of slow but certain solubility which enables this fungicide to exert for a considerable period a continuous repressive and lethal effect upon germinating bunt spores whether held upon the seed or occurring in the soil in the immediate vicinity of the seed. Bulletin 364] FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT 555 As copper carbonate is normally manufactured for use in the arts, and not for fungicidal purposes, no special efforts were made to standardize its chemical and physical composition. At the incep- tion of the experiments with copper carbonate dust, variations in its chemical and physical composition were noted. These variations were reflected in its efficiency as a preventive of bunt. Farmers complained of this condition and requested information concerning standards of TABLE 10 Chemical Analysis of the Four Lots of Copper Carbonate, the Effectiveness of which is Eeported in Table 8 Sample Number Chemical Analysis in Per Cent Copper (Cu)...,_ Carbon dioxide (C0 2 ) Hydroxylion (OH) .* Sulfuric anhydride (S0 2 ) Iron (Fe) Calcium oxide (CaO) Loss on ignition Insoluble residue 54.4 19.4 14.0 tr. v.sm. 29.4 53.8 18.3 14.4 v.sm. 30.3 small 46.6 15.9 16.3 some' 30.2 small 21 8 7 27 24 21 Recombined as Salts Copper carbonate (CuC0 3 ) Copper hydrate Cu (OH) 2 Copper sulfate (CuS0 4 ) Basic copper carbonate CuC0 3 .Cu (OH) 2 . 54.6 40.3 94.9 51.5 41.5 93.0 44.8 46.9 92.0 24.3 20.7 45.1 Density — Physical Fineness Pounds per cubic foot 28.12 43.75 76.25 36.25 1 Analyses by Prof. M. E. Jaffa, Harold Goss and Thos. B. Swift. * We are indebted to Prof. M. E. Jaffa and Mr. Harold Goss of the University of California, and Mr. Thos. B. Swift, for the analyses in table 10. purity and efficiency. Analyses were made of various samples of copper carbonate dust sold to the farmers. Representative samples were tested for bunt control and reported in table 8. Chemical analyses of these samples are given in table 10.* In regard to bunt control, one of the samples (No. 3, table 8) gave poor results. This sample contained but slightly less copper (No. 3, table 10) than those samples which gave good results. On examin- ation it was found to be gritty and to contain crystals blue in color. Zinc oxide was present in considerable quantities, together with quan- 556 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION tities of soluble chlorides and other salts. Sample No. 4 contained sulfates in large quantities, apparently in the form of calcium sulfate. The calcium sulfate may have resulted from the peculiar processes of manufacture, or from addition of calcium sulfate as a dilutant. As has been shown in numerous experiments (table 7), the addition of various quantities of lime (CaC0 3 ) or gypsum (CaS0 4 .2H 2 0) caused a corresponding reduction in efficiency of bunt control. The addition of dilutants appears to be a practice of doubtful value. The results indicate that the farmer should use the best and purest copper carbonate dust obtainable, even at an increase in price over less efficient and less costly copper carbonate compounds. It is difficult to increase copper carbonate in basic copper car- bonate beyond 55 per cent. By comparing the per cent of this copper carbonate with copper in satisfactory samples, it is seen that copper and copper carbonate are approximately equal. Wide departures from this proportion should be carefully scrutinized. The first three samples of copper carbonate dust employed in the experiments in table 8 contained sufficient quantities of copper to insure good results, judging by comparative analyses (table 10). However, No. 3 gave poor bunt control. On examination, its physical condition was found to be poor — that is, the particles were coarse, and the fine, silky feeling common to the best samples was lacking. This led to the examination of fineness of the particles of copper carbonate dust in order to arrive at a reasonable standard for fineness. The results of the physical analyses of four samples tested in table 8 are reported in table 10. In determining the physical condition of copper carbonate dusts, two tests were found necessary: (1) the determination of the density (weight of a given volume) of the dust, and (2) the fineness of the dust particles. The density was determined by shaking down a given weight in a measured cylinder, and the fineness by passing the material through a 200-mesh sieve while in aqueous suspension. By these tests those samples which gave the best control of bunt were found to average about 31 pounds per cubic foot. Over 99 per cent of this material passed through the 200-mesh sieve. On the other hand, it should be noted that the copper carbonate (sample No. 3, table 8) which gave the poorest bunt control returned the highest density, 78.84 pounds per cubic foot, with reduced quantities, 91.85 per cent passing through the 200-mesh sieve (sample No. 3, table 10). As the amount of copper (47.3 per cent) was not too low for fair results, the lack of bunt control may be charged to the excessive density and coarseness of the material, i.e., poor physical condition. Bulletin 364] FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT 557 SUGGESTED QUALITIES FOR A STANDARD COPPER CARBONATE With a method as new as the copper carbonate dust treatment, it is difficult to fix a standard for chemical and physical qualities. The experiments conducted at Davis, and the reports from farmers over the Pacific Coast States, indicate the necessity for an approximate TABLE 11 Comparison of the Per Cent of Copper in a Number of Commercial Lots of Copper Carbonate Basic Sample No. Copper (Cu) Per Cent Copper carbonate (CuC0 3 ) Per Cent Copper hydrate (Cu(OH) 2 ) Per Cent Copper sulfate (CuS0 4 ) Per Cent Calcium oxide (CaO) Per Cent Iron (Fe) Per Cent copper carbonate CuC0 3 .Cu (OH) 2 ) Per Cent Density lbs per cubic ft. 1 54.37 54.14 39.93 .30 .48 94.07 30.90 2 53.12 51.76 46.81 .76 98.57 3 55.80 54.97 43.46 .57 98.43 4 50.80 3.81 55.81 39.81 .75 2.30 59.62 5 47.32 60.38 23.59 5.90 ( 3 ) .81 .47 83.97 78.84 6 12.85 29.73 23.54 35.70 36.410) .35 53.27 34.71 7 21.90 25.01 19.74 15.55 24.33 .54 44.75 31.88 8 55.80 65.41 34.01 .65 99.42 9 53.24 8.87 48.78 42.57 .56 .66 57.65 55.82 10 51.88 1.19 93.70 11 55.58 65.41 33.69 .65 99.10 12 54.11 55.75 39.05 tr. .56 94.80 13 54.40 54.61 40.38 v. small tr. 94.99 28.12 14 53.80 51.51 41.50 v. small 92.01 43.75 15 53.30 51.48 40.55 small 92.03 35.00 16 46.60 48.80 46.95 some 95.75 76.25 17 50.60 52.61 40.47 small 93.08 62.50 18 53.80 52.35 38.92 v.v. small tr. 91.27 51.25 19 21.30 24.38 20.75 v.lge( 2 ) .73 45.13 36.25 20 52.90 53.68 39.20 large 92.88 66.35 Copper average in 12 uniform samples 55.30 per cent Copper carbonate average for the same 12 samples 53.96 per cent Copper hydrate average for the 12 samples 39.83 per cent 1 The calcium oxide combined as calcium carbonate in this mixture. 2 The calcium oxide is here combined as barium sulfate in large proportions. 3 This material is zinc oxide which may be combined as zinc sulfate. standard. The results of experiments reported in tables 10 and 11 indicate that the following qualifications for copper carbonate dust may be required without materially adding to the cost of manu- facture, but which will at the same time provide the farmer with an effective copper carbonate dust: 558 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 1. Copper carbonate dust should consist of 51 to 54 per cent of CuC0 3 and 39 to 42 per cent of Cu(OH) 2 . The former may range from 50 to 60 per cent, and the latter from 35 to 48 per cent of the dust, but best results may be anticipated from the more regular com- position. The combination of CuC0 3 .Cu(OH) 2 should comprise 94 Fig. 5. — California Dusting Machine, front view. per cent of the fungicide, but may vary from 92 to 98 per cent for good material. 2. Copper should not be less than 50 per cent, may average 53 per cent to advantage, and may rise to 55 per cent of the dust. It should be found solely in the carbonate and hydrate forms and not as sulfates or oxide. BULLETIN 364] FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT 559 3. Inert or foreign matter may include iron, silica, and slight amounts of sodium sulfate and non-fungicidal material not to exceed 6 or 7 per cent. Fig-. 6. — California Dusting Machine, rear view. 4. Copper carbonate dust should not be of greater density than 32 pounds per cubic foot when shaken down in a graduated tube. Lower density is desirable. 5. Not less than 99 per cent of the copper carbonate dust in aqueous suspension should pass through a 200-mesh sieve. 560 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION MACHINES FOE APPLYING COPPER CARBONATE DUST In Australia copper carbonate dust has given good results, 7 ' 8 > 9 - 10 but has not been used extensively except by small farmers. This, it is stated, is due to the lack of proper machinery for applying the dust thoroughly and economically to large quantities of seed. 7. — California dusting machine. Side view showing sprockets and opening Dden container. Fig. < . — v^fcui to the wooden container. The barrel churn has been used where small lots are treated. A modification of the barrel churn, or concrete mixer, has been put out by the Division of Agronomy of the University of California Experiment Station. This machine is a modification of the Washing- BULLETIN 364] FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT 561 ton State College smut treating machine. 14 It is constructed almost entirely of wood and can be made on the farm with common tools if the wheels and sprockets for tumbling the container be provided. It has a capacity of one sack of seed wheat every five minutes. Two minutes are required to mix the seed and dust and three minutes for filling, emptying and charging with the dust. Blueprints of this machine may be secured from the Agricultural Extension Service Division, at Berkeley. to'WSC plan Fig. 8. -California dusting machine. Diagram. UNIVERSITY,? CALIFORNIA COLLEGE: „ AGRICULTURE B£XK£L.£ Y. CAC/FOAH/A SMUT TREATING MACWA/E •Scale /^ m =/rr- /Vox /, /9ZZ Machines patterned after the automatic screw elevator type of machine, such as used in whitening smutty or dark colored barley at the large exporting warehouses, are in use. This type of machine automatically receives the seed and dust, mixing them in the passage of the seed through the enclosed screw elevator, but the loss of dust into the air is detrimental to workers. A very successful automatic duster is in use at Westhaven, Fresno County. The principle on which the process depends consists in gravity action operating as the seed is received from the cleaner and grader. Copper carbonate dust is automatically blown into the top of the machine and is sucked down through it by means of a fan driven by a % h.p. electric motor. Baffle boards tumble the descend- ing grain, mixing it thoroughly with the fungicidal dust. This 562 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION machine is simpler than the others and far less costly in construction. It is air-tight, being made of tongue and groove lumber. No dust escapes except at the sack filler, and here in such small quantities that the operator does not require a mask. In size it is 116 inches high, and 36 inches by 19 inches for the cross section. It is designed SEED CONDITIONER AND DUSTER APPARATUS Fig. 9. — Universal duster. Cleaned and graded seed received at the upper end. The dust is mixed by gravity and a forced blast. Capacity: 150 to 300 bushels per hour. No dust mask was required when the machine "was well fitted and thoroughly varnished to fill all cracks. Frederick Steigmeyer, Inventor. Patent applied for. Fig. 10. — Diagram of the Universal dust- ing machine. to thoroughly dust 150 bushels per hour, but can be adjusted to double this capacity. When used in connection with seed cleaning machinery, no extra help is required, as the grain may either be sacked or elevated to a bin and stored awaiting seeding time. This type of dusting machine should be very serviceable in connection with grain elevators or warehouses where seed is cleaned, graded and sold. A centralized treating plant equipped with such a machine might BULLETIN 364] FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT 563 well be operated by the farm bureau or similar organizations. With little or no additional expense beyond the cost of the copper carbonate dust, seed wheat may be treated ready for seeding at time of cleaning. Automatic seed treatment by this method should cheapen this process much below the cost to the farmer under ordinary farm operations. Loss of time may be eliminated at the seeding season by treating the seed in advance since no seed injury results from storing seed treated with copper carbonate dust. 14 It is hoped that this dusting of seed wheat with copper carbonate dust by automatically operated machinery will lead to universal seed treatment. If such practices could be put continuously into effect, there is evidence that bunt might be reduced to a small minimum, and in many areas entirely eliminated. EFFECT OF COPPER CARBONATE DUST UPON OPERATORS Many complaints have been received concerning the nauseating effect of copper carbonate dust when inhaled. In some instances farmers have reverted to the liquid treatment of seed wheat, even though the copper carbonate method is preferable, because of this irritating quality of the dust. In the process of manufacture it causes the same trouble, but the use of masks permits the operators to work indefinitely in its presence without injury. The mask found to give the best service at these plants (fig. 11) depends in one form upon a wet sponge for its effectiveness and in the other on a dry filter paper. Both are light and permit easy breathing and ordinary con- versation while working. The cost retail is $1.75 and $2.00 each. If the worker cannot secure a mask, it is possible to avoid con- siderable dust irritation by tying a wet bandana handkerchief or similar cloth over the nose and mouth. Although no feeding tests have been made, it does not seem advis- able to feed wheat which has been treated, because copper carbonate is poisonous. DEMONSTRATIONS WITH COPPER CARBONATE DUST ON FARMS Many demonstrations were made on California grain farms in 1921. 24 In 1922, cooperative demonstrations were made in eighteen counties, under the direction of farm advisors or county agents. Almost 15,000 acres were sown with copper carbonate dusted seed. Similar demonstrations were held in Washington 31 and Oregon. 1 The results secured for the 1922 harvest in these three Pacific Coast states are recorded in table 12. 564 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION The control of bunt by copper carbonate dust, as shown in the records of table 12, indicate that : in California it is almost completely effective; in Washington, more so than other fungicides; and in Oregon, as efficient as bluestone. Since bluestone, bluestone-lime, and iiSffy-fU'. w Fig. 11. — An effective device which carbonate dust. successfully prevents inhalation of copper formaldehyde are recognized preventives of infection from seed- borne spores, the lack of complete control denotes either that the seed was too heavily smutted or that the attack came from bunt-infested soil and was therefore beyond the reach of fungicides applied to the seed. The details of these investigations are reported in the discussion which follows. BULLETIN 364] FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT 565 A critical point in bunt control lies in the thorough application of the copper carbonte dust to the seed. Lack of intimate mixing has been reported as the cause for lack of better control. So tenacious are the small amorphous particles of copper carbonate that with a low power microscope they are seen to adhere to every portion of the seed coat in a manner not unlike that of the bunt spores themselves. Even when dusted seed wheat is sown by the broadcast seeder, the particles of copper carbonate dust still adhere to all parts. In the TABLE 12 Summary of Bunt Control Tests with Copper Carbonate in the Pacific Coast States for the 1922 Harvest Counties reporting Farms reported Bunt, untreated seed Bunt, bluestoned seed Bunt, bluestone-limed seed Bunt, formaldehyded seed Bunt, formaldehyde-lime seed. Bunt, copper carbonate Washington 0) Num- ber trials 9 75 8 28 10 33 3 75 Bunt per cent 93.7 10.7 9.0 6.9 6.6 5.4 Oregon 0) Num- ber trials 31 17 1 14 31 Bunt per cent 0.0 2.4 0.0 0.8 0.0 2.3 California Num- ber trials 18 40 31 16 7 8 35 Bunt per cent 6.0 3.0 2.0 2.0 0.0 .6 1 These tests were conducted under the supervision of county agents and reported for Oregon by Prof. H. P. Barss, 1 Plant Pathologist, Oregon Agricultural Experiment Station, and for Washington by Prof. George L. Zundel, 28 Extension Plant Pathologist of the Washington State College. drill, friction removes bnt little of the dust, and in addition any excess dust over that held by the seed coat is sown with the seed, adding to its effectiveness. Farmers have complained of poor bunt control by copper car- bonate compounds lacking in physical fineness and chemical purity similar to the qualifications set forth in table 10. The absence of germ injury to seed wheat treated with copper carbonate has been conclusively demonstrated by hundreds of care- fully controlled tests. Everywhere farmers have observed the same results. While complaints of seed injury caused by formaldehyde and bluestone treatments have been frequent, none have been received against copper carbonate. According to the reports from county agents on the Pacific Coast, the percentage of plants per acre for copper carbonate-treated seed, compared with other seed treatments, 566 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION is greater by 30 to 50 per cent, but in many cases the range is much greater. Occasionally some farmer complains of too thick a stand from copper carbonate treated seed. Certainly a better stand is secured from copper carbonate-treated seed than from seed treated with either bluestone or formaldehyde-treated seed sown at the same rate. Many farmers report that the copper carbonate-dusted seed sprouted several days ahead of seed otherwise treated, or untreated. When these fields have been contrasted, the differences are quite evident. Stimulation of seedlings by copper carbonate frequently pushes them out of the soil before crusts form to delay emergence. Thicker stands have caused weed suppression and increased yields. The majority of the farmers who used copper carbonate dust in 1922 report better yields from fields sown with dusted seed than from fields sown with seed treated by liquid fungicides, or from fields sown with untreated seed. Farm tests are more or less variable, owing to variations in appli- cation of the fungicide and the spore load. Soil infestation by bunt spores also disturbs bunt control. The application of copper car- bonate dust will undoubtedly be improved when serviceable dusting machinery is available. It is not to be expected that this dust fungicide will give better control of seed-borne bunt than the standard solutions, but that it will equal them in this respect except when the seed is blackened with bunt spores. Though the control of bunt by copper carbonate is no better than with the standard fungicide, the increase in the number of plants and heads per acre has resulted in better yields. These outstanding advantages following the use of copper carbonate should result in the general adoption of this dust fungicide as a bunt preventive. SOURCES OF COPPER CARBONATE Difficulty in securing copper carbonate in sufficient quantities has been encountered. If the use of this fungicide is to become general, then sufficiently large supplies should be available to meet all needs. Three sources of supply exist: (1) importations from Germany; (2) manufacturers on the Atlantic seaboard; and (3) local manufacturers. The copper carbonate from abroad and from eastern sources is manu- factured for the metallic arts and not for use as a dust fungicide, and it may be at times too coarse for entirely successful control of infection from seed borne spores. No doubt this difficulty can be BULLETIN 364] FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT 567 remedied if special orders are placed for copper carbonate of a speci- fied physical quality and chemical purity. In the San Francisco bay region three or four chemical concerns are now manufacturing copper carbonate dust for use as a fungicide. By consultation with these firms the specifications for the qualities of effective copper carbonate have become understood, and improvement in the quality of the fungicide put out has followed. Owing to the comparative newness of the dust method for bunt control, manufacturers are reluctant to create large stocks which may remain unsold. Many farmers complain, however, that they have had to treat their seed by the old methods for lack of supplies of copper carbonate. In 1920, only a few ounces were used ; in 1921, about 12,000 to 15,000 acres were sown with treated seed ; but in 1922, estimates place the acreage at more than 250,000. SUMMARY 1. Many fungicidal solutions, though destructive to bunt spores on the seed, injure and destroy seed germs. Distorted plants, delayed growth, and poor stands frequently occur. Bluestone represses root growth, and formaldehyde represses plumule development. 2. All poor stands are not caused by seed treatment, for soil and weather conditions prevent a large jjortion of the seed from develop- ing into seedlings. A reduction of germination to almost 50 per cent occurs commonly on the University Farm at Davis, California (table 9). 3. Seed treated by fungicidal solutions showed reductions in germ- ination in the soil when compared with laboratory germinations in 112 tests as follows : Formaldehyde 96.3 to 41.5 per cent Bluestone 38.1 to 31.4 per cent Bluestone-lime 73.6 to 39.6 per cent 4. Flowers of sulfur reduced bunt to about one-tenth of the infec- tion which occurred in similar unsulfured seed even where the dosage of smut spore was light. Sulfur is not a dependable bunt fungicide. 5. The amount of bunt in a crop depends in large part upon the quantity of bunt spores borne by the kernel. The per cent of bunt decreases with the spore dosage. 6. Bluestone powder applied to seed at the rate of two or three ounces per bushel is almost as effective as copper carbonate in con- trolling bunt infection. The difficulty of its use lies in the fact that 568 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION it may not retain its powdered form because it becomes massed by absorbing moisture. Therefore, if copper carbonate dust is not avail- able, bluestone powder or anhydrous copper sulfate may be used as a fair substitute. 7. Copper carbonate dust applied to seed wheat at the rate of two ounces or more to the bushel effectively controls bunt when the seed is not blackened with spores. For heavily bunted seed, bluestone and formaldehyde solutions are more effective, but are liable to cause severe seed injury. 8. Seed wheat treated with copper carbonate dust is not injured by the fungicide even when held in storage for an indefinite period. This permits the treating of seed during the slack season, thus avoid- ing loss of valuable time during seeding operations. 9. Germination of seed wheat is not inhibited by copper carbonate dust. Excellent stands usually are secured and less seed required per acre than when fungicidal solutions are used. Seed treated by the standard liquid methods frequently have to be sown 30 to 70 per cent heavier than is necessary for copper carbonate-dusted seed (table 9). 10. Seed treated with copper carbonate dust germinates earlier and makes a more vigorous seedling growth than seed treated with fungicidal solutions. Prompt emergence from the soil and early root development combined with a superior stand are usually reflected in an increased yield. 11. Dilution of copper carbonate dust does not appear to be warranted because: (1) only a limited quantity can be retained upon the surface of the seed (less than two ounces per bushel) ; (2) diluted copper carbonate dust applied at two ounces per bushel is not com- pletely effective in bunt control; and (3) dilutions may favor poor processes in manufacture, resulting in inferior bunt control (table 6). 12. The best standard for effective copper carbonate dust appears to be as follows : Copper in the form of copper carbonate (52 to 54 per cent) and copper hydrate (39 to 42 per cent), totaling 93 to 94 per cent of these two, with impurities amounting to 6 or 7 per cent of the whole mass. Fineness : Ninety-nine per cent in aqueous solution should pass through a 200-mesh sieve. Density after shaking down dry : not over 32 lbs. per cubic foot. Color: light green, never blue. Bulletin 364] FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT 569 13. Copper carbonate dust when inhaled causes nausea and other forms of irritation. These inconveniences can be avoided by wearing a dust mask as prescribed by law for workers in factories producing this and other chemical dusts. A wet sponge or wet handkerchief tied over the nose and mouth will give considerable relief. 14. A serious drawback to the extension of the copper carbonate dust treatment lies in the limited supply of the chemical. It may be imported, but it is then likely not to comply with the standards of fineness and purity demanded. A limited number of factories are now producing satisfactory copper carbonate dust in the San Fran- cisco bay region. 15. The price of copper carbonate usually is more than double that of bluestone. As copper carbonate contains more than double the amount of copper (52-55 per cent) contained in bluestone (25.04 per cent), from which it is made, this ratio is not unreasonable. How- ever, the saving in the cost of labor with the dust treatment is many times greater than this difference in price. 16. The greatest obstacle to the universal adoption of copper carbonate dust lies in the lack of proper machinery to dust econom- ically and effectively large quantities of seed in a short time. This difficulty is rapidly being overcome by the invention of automatic ducting machinery. This machinery should properly become part of the local warehouse or elevator where seed may be cleaned, graded and dusted at one operation, and stored ready for use. 17. A few reports unfavorable to the use of copper carbonate have come from other regions, 16 but in the great majority of instances the reports have been very satisfactory. Reports are now available from Australia, Canada, Denmark, Italy, and several parts of the United States. 5 - 13 - 19 > 25 18. Organic mercuric fungicides, usually consisting of chlor- phenol-mercuric compounds in varying porportions, have been found to be excellent bunt preventives without germ injury when used as solutions, but less effective when applied as dusts. These compounds : Chlorophol, 12 ' 27 > 28 Seedosan, Germisan, etc., are not readily available and are apparently very expensive. 19. All seed wheat should be treated every year because a slight quantity of bunt spores may cause wholesale infection, as each bunted kernel or gall contains from one to eight million spores. 4 570 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION LITERATURE CITED i Barss, H. P. Results of tests with copper carbonate. Harvest of 1922. Pre- liminary Report. Oregon Agric. Exp. Sta., Circ. 30. August 10, 1922. 2 Bolley, H. L. The use of the centrifuge in diagnosing the plant diseases. Proc. Soc. for the Prom, of Agric. Sci., 23:82-85. 1902. s Bolley, H. L. New work upon the smuts of wheat, oats, and barley, and a resume of the treatment experiments for the last three years. No. Dak. Agric. Exp. Sta, Bull. 27. 1897. 4 Cobb, N. A. Quantitative estimation of bunt spores in seed wheat. Agric. Gazette, New South Wales, 16:1113-1117. 1905. 5 Coons, G. H. Copper-dust treatment for stinking smut. Michigan Quarterly Bull., 5:1, pp. 8-11. August, 1922. 6 Darnell-Smith, G. P., and Carne, W. M. Effect of formalin on germination of plants. In 3rd Rept. Gov't. Bull. Microbiol. N. S. W. 1912. 7 Darnell-Smith, G. P. The use of copper carbonate as a fungicide. Agric. Gazette, N. S. W., 26 (1915), No. 3, p. 242. s Darnell-Smith, G. P. The prevention of bunt. Experiments with various fungicides. Agric. Gazette, N. S. W., 28:185-189. March 2, 1917. 9 Darnell-Smith, G. P., and Ross, H. A dry method of treating seed wheat for bunt. Agric. Gazette, N. S. W., 30:685-692. 1919. io Darnell-Smith, G. P. Fungicidal dusts for control of smut. Agric. Gazette, N. S. W., 32:796-798. 1921. ii Darnell-Smith, G. P. Dry copper carbonate for bunt. Agric. Gazette, N. S. W., 33 (1922), No. 10, pp. 754-755. 12 Heald, P. D. Div. of Plant Pathology. Wash. Coll. Sta. Bull. 167 (1922), pp. 38-43. is Heald, F. D., and Smith, L. J. The dusting of wheat for bunt or stinking smut. Wash. Agric. Exp. Sta. Bull. 168, p. 15. June, 1922. 14 Heald, F. D., and Smith, L. J. The dusting of wheat for bunt or stinking smut. Wash. State Coll. Agric. Exp. Sta. Bull. 171. October, 1922. is Heald, F. D. The relation of spore load to the per cent of stinking smut appearing in the crop. Phytopath., 11:269-278. 1921. 16 Hungerford, C. W. The News Letter. The University of Idaho. Published by the College of Agric. Vol. 8, No. 8. September 25, 1922. 17 Hurd, Annie May. Injury to seed wheat from drying after disinfection with formaldehyde. Jour. Agric. Res., V, No. 3. November 1, 1920. is Hurd, Annie May. Seed-coat injury and viability of seeds of wheat and barley as factors in susceptibility to molds and fungicides. Jour. Agric. Rec, Vol. 21, No. 2. April 15, 1921. is KiJHN, J. G. Krankheit die Kulturgewachse, p. 85, 1859. 20 Lambert, E. B., and Bailey, D. L. Results of treating seed of spring wheat and oats with copper carbonate dust to prevent smut. Phytopath., 12. 1922. BULLETIN 364] FUNGICIDAL DUSTS FOR THE CONTROL OF BUNT 571 21 Mackie, W. W. Seed treatments for the prevention of cereal smuts. Cal. Exp. Sta. Cire. 214. September, 1919. 22 Mackie, W. W., and Briggs, F. N. Fungicidal dusts for control of bunt. Science, n.s., Vol. 52, No. 1353, pp. 540-541. December 3, 1920. 23 Mackie, W. W., and Briggs, F. N. Chemical dusts for the control of bunt. Phytopath., 11:38-39. 1921. 24 McLeod, George E. Control of smut. Agric. Dept., Sperry Flour Co., Stock- ton, Calif. November 18, 1921. 25 Morettini, A. Sulla efficacia dei trattamenti polverulenti contro la "carie" del frumento. (Efficiency of powders for controlling smuts of cereals.) Trans, by Theo. Holm. Stoz. Sperim. Agric. Ital., Vol. 54, pis. 7-10 (Mo- dena), pp. 293-315. 1921. 26 Perkins, A. J. Eandom agricultural jottings. Jour. Dept. Agric. So. Africa, 23:287-290. 1919. 27 Eiehm, E. Prufungeiniger Mittel zur Bekampfung des Steinbrandes. (Experi- ments with some fungicides to combat bunt, or stinking smut.) Trans, by Theo. Holm. Nitth. aus d. Kais. Biol. Aust. f. Land. u. Forstwiss. Noft. 14, Berlin, pp. 8-9. 1913. 28 Eemy, Th., and Vasters, J. Beobachtungen ueber chlorphenol-quecksilber als Pflanzenschutzmittel. (Observations on Chlorphenol-Mercury as a Fungi- cide.) Trans, by Theo. Holm. Illust. Landwirt Zeitung, 34th year, Berlin, 1914, pp. 769-771. 29 Tubeuf, von Eeg. Eath, Dr. Freiherr, Studien ueber die Brandkrankheiten des Getreides und ihre Bekampfung. Mit 1 Tafel (VIII) und 19 Testfiguren Arbeiten aus der Biologischen abcheilung fur Land- und Forstwithschoft am Kaiserl. Gesundheitsamte. II pt. 4, Berlin. 1902. so Wheeler, W. A. Preliminary experiments with vapor treatments for the pre- vention of the stinking smut of wheat. So. Dakota Agric. Coll. Exp. Sta. Bull. 89. November, 1904. 3i Zundel, George L. Summary of copper carbonate treatment for the control of smut. State of Washington 1922 Crop. Wash. Agric. Exp. Sta. August 2, 1922. 572 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Fig. 12. — No. 3, bunted Propo head and bunt gall. No. 4, normal Propo head and kernel. When bunted plants are supplied with an excess of space, light, moisture and plant food, the disease may stimulate excessive growth as indicated here. STATION PUBLICATIONS AVAILABLE FOR FEEE DISTRIBUTION BULLETINS No. No. 253. Irrigation and Soil Conditions in the 332. Sierra Nevada Foothills, California. 334. 261. Melaxuma of the Walnut, "'Juglans regia." 335. 262. Citrus Diseases of Florida and Cuba Compared with these of California. 336. 263. Size Grades for Ripe Olives. 268. Growing and Grafting Olive Seedlings. 337. 270. A Comparison of Annual Cropping, Bi- 339. ennial Cropping, and Green Manures on the Yield of Wheat. 341. 273. Preliminary Report on Kearney Vine- 342. yard Experimental Drain. 343. 275. The Cultivation of Belladonna in Cali- 344. fornia. 276. The Pomegranate. 345. 278. Grain Sorghums. 279. Irrigation of Rice in California. 346. 280. Irrigation of Alfalfa in the Sacramento 347. Valley. 283. The Olive Insects of California. 348. 285. The Milk Goat in California. 349. 286. Commercial Fertilizers. 287. Vinegar from Waste Fruits. 350. 294. Bean Culture in California. 351. 297. The Almond in California. 352. 298. Seedless Raisin Grapes. 299. The Use of Lumber on California Farms. 353. 304. A study on the Effects of Freezes on 354. Citrus in California. 355. 308. I. Fumigation with Liquid Hydrocyanic 356. Acid. II. Physical and Chemical Prop- erties of Liquid Hydrocyanic Acid. 357. 312. Mariout Barley. 313. Pruning Young Deciduous Fruit Trees. 316. The Kaki or Oriental Persimmon. 358. 817. Selections of Stocks in Citrus Propa- gation. 359. 319. Caprifigs and Caprification. 360. 821. Commercial Production of Grape Syrup. 324. Storage of Perishable Fruit at Freezing 361. Temperatures. 325. Rice Irrigation Measurements and Ex- 362. periments in Sacramento Valley, 363. 1914-1919. 328. Prune Growing in California. 364, 331. Phylloxera-Resistant Stocks. Walnut Culture in California. Preliminary Volume Tables for Second- Growth Redwoods. Cocoanut Meal as a Feed for Dairy Cows and Other Livestock. The Preparation of Nicotine Dust as an Insecticide. Some Factors of Dehydrater Efficiency. The Relative Cost of Making Logs from Small and Large Timber. Studies on Irrigation of Citrus Groves. Hog Feeding Experiments. Cheese Pests and Their Control. Cold Storage as an Aid to the Market- ing of Plums. Fertilizer Experiments with Citrus Trees. Almond Pollination. The Control of Red Spiders in Decidu- ous Orchards. Pruning Young Olive Trees. A Study of Sidedraft and Tractor Hitches. Agriculture in Cut-over Redwood Lands. California State Dairy Cow Competition. Further Experiments in Plum Pollina tion. Bovine Infectious Abortion. Results of Rice Experiments in 1922. The Peach Twig Borer. Observations on Some Rice Weeds in California. A Self-mixing Dusting Machine for Applying Dry Insecticides and Fungicides. Black Measles, Water Berries, and Related Vine Troubles. Fruit Beverage Investigations. Gum Diseases of Citrus Trees in Cali- fornia. Preliminary Volume Tables for Second Growth Redwood. Dust and the Tractor Engine. The Pruning of Citrus Trees in Cali- fornia. Fungicidal Dusts for the Control of Bunt. CIRCULARS No. No. 70. Observations on the Status of Corn 166. Growing in California. 167. 82. The Common Ground Squirrel of Cali- 170. fornia. 87. Alfalfa. 172. 110. Green Manuring in California. 173. 111. The Use of Lime and Gypsum on Cali- fornia Soils. 174. 113. Correspondence Courses in Agriculture. 175. 117. The Selection and Cost of a Small Pumping Plant. 178. 127. House Fumigation. 179. 136. Melilotut indica as a Green-Manure Crop for California. 182. 144. Oidium or Powdery Mildew of the Vine. 148. "Lungworms." 183. 151. Feeding and Management of Hogs. 184. 152. Some Observations on the Bulk Hand- 188. ling of Grain in California. 190. 155. Bovine Tuberculosis. 193. 157. Control of the Pear Scab. 198. 159. Agriculture in the Imperial Valley. 199. 160. Lettuce Growing in California. 201. 161. Potatoes in California. 202. 165. Fundamentals of Sugar Beet Culture under California Conditions. 203. The Country Farm Bureau. Feeding Stuffs of Minor Importance. 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. The Packing of Apples in California. Factors of Importance in Producing Milk of Low Bacterial Count. Extending the Area of Irrigated Wheat in California for 1918. Infectious Abortion in Cows. A Flock of Sheep on the Farm. Lambing Sheds. Agriculture Clubs in California. A Study of Farm Labor in California. Syrup from Sweet Sorghum. Onion Growing in California. Helpful Hints to Hog Raisers. County Organizations for Rural Fire Control. Peat as a Manure Substitute. CIRCULARS — Continued No. 205. 206. 208. 209. 210. 212. 214. 215. 217. 218. 219. 224. 228. 230. 232. 233. 234. 235. 236. 237. Blackleg. Jack Cheese. Summary of the Annual Reports of the Farm Advisors of California. The Function of the Farm Bureau. Suggestions to the Settler in California. Salvaging Rain-Damaged Prunes. 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. The Present Status of Alkali. Control of the Brown Apricot Scale and the Italian Pear Scale on Decid- uous Fruit Trees. Vineyard Irrigation in Arid Climates. Testing Milk, Cream, and Skim Milk for Butterfat. Harvesting and Handling California Cherries for Eastern Shipment. Artificial Incubation. Winter Injury to Young Walnut Trees during 1921-22. Soil Analysis and Soil and Plant Inter- relations. The Common Hawks and Owls of Cali- fornia from the Standpoint of the Rancher. Directions for the Tanning and Dress- ing of Furs. No. 238. 239. 240. 241. 242. 244. 245. 246. 247. 248. 249. 250. 251. 252. 253. 254. 255. 256. 257. 258. 259. The Apricot in California. Harvesting and Handling Apricots and Plums for Eastern Shipment. Harvesting and Handling Pears for Eastern Shipment. Harvesting and Handling Peaches for Eastern Shipment. Poultry Feeding. Central Wire Bracing for Fruit Trees. Vine Pruning Systems. Desirable Qualities of California Bar- ley for Export. Colonization and Rural Development. Some Common Errors in Vine Pruning and Their Remedies. Replacing Missing Vines. Measurement of Irrigation Water on the Farm. Recommendations Concerning the Com- mon Diseases and Parasites of Poultry in California. Supports for Vines. Vineyard Plans. The Use of Artificial Light to Increase Winter Egg Production. Leguminous Plants as Organic Fertil- izer in California Agriculture. The Control of Wild Morning Glory. The Small-Seeded Horse Bean. Thinning Deciduous Fruits. Pear By-products.