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.
------- |