EPA-540/9-77-015 PARTICLE SIZE OF HOME AND GARDEN PESTICIDES CONTAINING FUNGICIDES JUNE 1977 U.S. Environmental Protection Agency Washington, D. C. 20460 ------- PARTICLE SIZE OF HOME AND GARDEN PESTICIDES CONTAINING FUNGICIDES H. L. Dooley Northwest Biological Investigations Station, Technical Services Division, U. S. Environmental Protection Agency, 3320 Orchard Avenue, Corvallis, Oregon 97330 June 1977 EPA-540/9-77-015 ------- PARTICLE SIZE OF HOME AND GARDEN PESTICIDES CONTAINING FUNGICIDES H. L. Dooley ABSTRACT Nineteen different commercial home and garden pesticide formulations containing fungicides from 17 manufacturers were evaluated for particle size by wet- and dry-sieve methods. Significantly different results were obtained by each method. The wet-sieved method showed that at least 90% of the particles were smaller than 75 urn in 17 formulations, while the dry-sieved method indicated that 70% of the particles were smaller than 75 urn in only seven formulations. The dry sieving method was found to be most appropriate for the evaluation of dusts. The mean particle size of most currently marketed commercial pesticide dusts for home and garden use is 149 urn or smaller. The relationship between particle size and pesticide effectiveness is well known (4, 5, 6, 7, 8, 9, 10). Pesticide manufacturers frequently specify the portion of their product that will pass a 325-mesh sieve (i.e. 44 um). Methods for particle size determination vary among manufacturers, but wet and dry sieving are most common (1, 2). The work reported here was undertaken to determine the particle size of commercially available home and garden pesticide dusts containing fungicides and to compare the two methods used for determining size. MATERIALS AND METHODS Home and garden pesticide formulations often contain both fungicides and insecticides. Fungicldal components involved in this study were: Folpet, Folpet plus sulfur, Chlorothalonil plus Karathane, zinc salts, and a copper zinc chromate complex. A sulfur compound and a copper zinc chrornate complex were the only products that did not contain insecticides in their formulation. ------- Both dry- and wet-sieving (1, 2) methods were evaluated in this study. Nineteen pesticide dust formulations registered for domestic use, including 60 different samples collected from 17 distributors, were sieved using both methods. Dry sieving; Three aliquots containing 10 g each of each pesticide formulation were Independently dry sieved through a nest of Tyler standard sieves consisting of 149, 74, and 44 urn openings (100, 200, and 325-meshes per inch). The samples were placed on the top s^eve (149 urn) and the nest was shaken for 10 minutes on a model R202 Tyler Portable Sieve Shaker. Dust remaining on each sieve and in the bottom pan was weighed at the conclusion of the shake cycle and the mean percent weight of the material on each sieve was calculated. Wet sieving: Three aliquots containing 10 g each of each pesti- cide formulation were Independently wet sieved through a nest of Tyler standard sieves consisting of 149, 74, and 44 urn openings (100, 200, and 325-meshes per inch). The sieves were thoroughly wet with tap water before the sample was placed on the upper sieve of the nest. Then the sample was washed through the sieves with a continuous stream of tap water (about 1100-1200 ml/minute). Samples were considered completely sieved when the water passing the 44 jan sieve was clear. Material retained on each sieve was individually washed into a separate petri dish and the uncovered dishes were placed in a drying oven at 27 C for 24 hours. After cooling, weights of the pesticide formulation were determined and the mean percent weight of material on each sieve was calculated. ------- RESULTS AND DISCUSSION The percentage of each dust retained on 100, 200, and 325-mesh sieves and the percentage that passed the 325-mesh sieve were expressed as particle size groups based on sieving behavior (Table 1). More than 70% of the particles in formulations A, B, C (Folpet), H (Folpet plus sulfur), J (Captan), P (sulfur), and Q (Karathane plus Chlorothalonil) were smaller than 75 um as determined by the dry-sieve method. However, more than 90% of the particles of 17 wet-sieved formulations contained particles smaller than 75 jim. Formulations L (Captan), R (copper zinc chromate), and S (zinc salts) contained the majority of particles larger than 149 um by the dry-sieve method. Eighty percent of the particles from Folpet (A), Captan (J and L), and sulfur (P) formulations measured less than 45 jim in size when tested by the wet-sieve technique. The particle size distribution of similar dry-sieved formulations was often distinctly different. For example, in one Captan formulation (J) less than 1% of the particles were greater than 150 jim but in a similar formulation (L) over 74% of the particles were larger than 150 /um. A similar disparity of particle size distribution occurred with two similar Folpet formulations (A vs. G). Smaller particles may cause over-application when used in plastic squeeze dusters (3). It is difficult to achieve uniform coverage with these dusters when the dust formulation is principally composed of small particle sizes. For example, with formulation A approximately 2.8 times as much dust was applied as when plants were dusted with similar formulation G. Formulations which contain smaller particles may result in over application and reduce photosynthesis of the leaves ------- unless the excess dust is removed following application. Larger parti- cles applied with plastic squeeze dusters may result in poor distribution of the dust on the leaf surface if the duster orifice becomes clogged. Particle size affects applicator effectiveness. This work demonstrates that the method by which particle size is determined is an important factor in achieving desired results. Because dusts are applied dry, the most appropriate method of evaluation is dry sieving. Both the wet- and dry-sieving methods are necessary to determine particle size of products which may be used as dusts or sprays. Significant differences between aliquots did not exist and consistent results were obtained using both methods. The amount of pesticide formulation to be sieved is Important. Ten grams of material can be sieved without overloading the sieves. Therefore, 10 gram aliquots were used. Material may be effectively sieved in 10 minutes provided that only three sieves are used. Samples containing Folpet as the only fungicide ingredient were from different manufacturers (except E and F). All other samples containing the same fungicide components were from different manu- facturers. The results illustrate that various manufacturers strive for different particle size ranges or have poor quality control. Some manufacturers may blend fungicides and Insecticides of different particle sizes to prepare combination products. Particle size is not regulated unless specified on the product label but can be an important factor in product effectiveness. ------- !. Jartlcle slze dl3trlbutlon oŁ Pesticide Sample desig- nation A B C D E F G H I J K L M N 0 P Q R S No. of samples tested 4 6 3 2 3 3 1 1 11 2 2 3 4 2 5 2 3 2 1 Fungicide content Folpet Folpet Folpet Folpet Folpet Folpet Folpet Folpet Sulfur Folpet Sulfur Captan Captan Captan Captan Sulfur Captan Sulfur Captan Sulfur Sulfur 5% 5% 6.5% 5% 5% 7.5% 5% 7.5% 10% 7.5% 30% 5% 4% 5% 5% 20% 4% 25% 10% 25% Karathane 0.9% Chlorothalonil 5% Copper Zinc Chromate 89% Zinc 3 .9% Percentage > 150 urn Dry 1.3 1.6 2.3 3.6 5.5 22.4 14.2 6.1 26.2 0.7 39.5 74.6 15.2 37.8 12.3 0.7 1.4 53.8 76.6 Wet 0.3 0.3 0.1 0.1 0.6 0.3 0.1 2.7 0.1 0.2 0.2 13.7 2.3 0.4 1.0 17.2 0.1 0.4 0.1 of pesticide in various 75-149 urn Dry 3.0 12.5 15.1 36.0 30.0 52.9 33.7 16.5 56.4 6.1 41.7 3.2 42.1 39.2 70.2 3.2 15.0 34. A 16.9 Wet 9.3 1.8 2.2 3.1 1.2 2.4 1.5 2.3 2.9 4.1 2.1 10.1 2.3 2.8 4.0 6.1 1.0 1.2 2.3 45-74 urn Dry 12.3 30.5 33.5 29.4 50.0 17.8 47.0 56.6 10.6 26.9 12.2 19.3 24.2 17.1 12.1 19.3 33.5 3.5 2.5 Wet 45.0 13.1 14.9 6.8 5.7 5.2 5.2 8.5 7.0 25.1 16.5 9.3 7.5 11.3 20.0 16.7 6.6 1.6 5.3 particle size groups < 44 w Dry 83.2 54.7 45. 7' 31.0 14.6 7.0 5.1 20.8 5.0 66.3 6.7 2.9 18.5 5.9 5.3 76.9 50.2 8.3 3.9 Wet 45.3 84.6 82.8 90.1 92.5 92.1 93.2 86.5 90.0 70.7 82.2 66.8 87.9 '85.5 75.0 60.1 92.3 96.8 92.3 ------- Literature Cited 1. American Society for Testing and Materials. 1969. Manual on Test Sieving Methods. ASTM Special Tech. Publ. 447. 43 pp. 2. CIPAC Handbook. 1970. Analysis of Technical and Formulated Pesticides. Collaborative International Pesticides Analytical Council Limited. W. Heffer and Sons Ltd., Cambridge, England. Vol. 1. 1079 pp. 3. Dooley, H. L. 1971. Application Characteristics of Plastic Squeeze and Pump Gun Type Garden Dusters. Plant Dis. Reptr. 55:1014-1017. 4. Lyle, E. W. 1943. Black-Spot on Rose Canes. Amer. Rose Annu. 28:155-156. 5. Massey, L. M. 1939. Fungicides for Roses. Amer. Rose Annu. 24:103-111. 6. Massey, L. M. 1946. Blackspot Can Be Controlled. Amer. Rose Annu. 31:111-119. 7. Meyer, L. J. 1930. Dusting Roses. Amer. Rose Annu. 15:79-81. 8. Robinson, R. H. 1922. The Physical Properties of Commercial Arsenates of Lead. The J. of Ind. and Eng. Chem. 14:313-317. 9. Streeter, L. R. 1927. Physical Properties of Commercial Dusting and Spraying Materials. N. Y. State Agr. Exp. Sta. Geneva Tech. Bull. 125. 12 pp. 10. Thatcher, R. W. and L. R. Streeter. 1925. The Adherence to Foliage of Sulfur in Fungicidal Dusts and Sprays. N. Y. State i Agr. Exp. Sta. Geneva Tech. Bull. 116. 18 pp. ------- |