Parathion Spray Residue on Soft Fruits, Apples, and Pears KENNETH C. WALKER
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Washington Agricultural Experiment Stations, Wenatchee, Wash.
The amount of parathion spray residue on soft fruits is roughly proportional to the length of time between date of application and date of analysis. Parathion spray residue was lost from the surface of Delicious apples at the rate of 80 to 85% in 12 to 13 days and 93 to 100% in 30 to 32 days. The rate of loss was the same for 1-pound as for 4-pound concentrations. Fifty-five samples, collected from commercial orchards, were analyzed. No significant relationship was found between the number of days between spraying and analysis and the parathion residue. There was no significant difference in parathion residue due to the concentration of the spray mixture used. All residues were only a fraction of 1 p.p.m.
Parathion (0,0-diethyl O-p-nitrophenyl thiophosphate) is an ester of thiophosphoric acid with the empirical formula C10H14NO5PS. It is a high boiling deep-brown to yellow liquid, some samples of which possess a characteristic odor. Its boiling point has been calculated to be 375° C . or higher, at 760 m m . pressure ; its refractive index is n^ 1.15360 ; specific gravity is 1.26. The vapor pressure is 0.0006 m m . of mercury at 24° C . The technical grade has a purity of approximately 9 5 % . 5
Parathion is very slightly soluble i n water (20 parts per million), but is completely miscible i n many organic solvents including esters, alcohols, ketones, ethers, aromatic and alkylated aromatic hydrocarbons, and animal and vegetable oils. It is practically i n soluble i n such paraffinic hydrocarbons as petroleum ether, kerosene, and refined spray oils (about 2%) unless a mutual solvent is used (1). Parathion has been recommended i n the state of Washington (3) for the control of various species of mites and orchard aphids. Wettable powders, containing 15 or 2 5 % of parathion, have been used at concentrations ranging from 0.25 to 4 pounds per 100 gallons of water on an experimental basis and from 0.25 to 0.5 pound on a commercial basis.
Methods and Procedure Parathion spray residue on the surface of the fruit was determined b y the method of Averell and Norris (β). Samples of sufficient size of firm fruit completely to fill 1-gallon wide-mouthed glass jars were selected for analysis. The parathion was removed from the surface of the fruit with benzene (redistilled) in an end-over-end type tumbling machine at a speed of 72 revolutions per minute. A l l samples were washed i n this manner for a period of 0.5 hour. Reagent blanks and u n sprayed fruit blanks were run with all samples. A l l results, as reported, have been cor rected for reagent and fruit blanks. 123
AGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.
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124
Soft Fruit Although parathion has not been recommended to date for insect control on soft fruits, there are indications that some injurious insects may be controlled b y applications of parathion. Experimental sprays of 1 pound of the 2 5 % wettable powder per 100 gal lons of water were applied to soft fruits to determine the amount of parathion residue that would remain on the, surface at harvest time. The parathion residue at harvest time is presented i n Table I . Table I.
Parathion Residue on Surface of Soft Fruits at Harvest Time Days between Last Spray and Analysis
Surface Parathion, P.P.M.
Bing cherry
14 25 36 43
0.30 0.08 0.08 0.08
Morpark apricot
75 79 14 20 38 47 72
0.00 0.00 0.40 0.21 0.00 0.01 0.02
Yakamine
28
0.03
Italian prune
60
0.00
Elberta peach
7 30 55 75 97
1.63 0.80 0.03 0.00 0.01
Golden Jubilee peach
38 38 53
0.57 0.76" 0.00
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Variety
Tilton apricot
J. H . Hale peach a
Two sprays of 2 pounds of 25% wettable powder per 100 gallons.
Parathion, used for the control of injurious insects on soft fruits, would be applied more than 30 days prior to harvest. Infestation of the various potential insects is relatively early i n the spring. Where sprays of 1 pound of 2 5 % wettable powder per 100 gallons of water were applied more than 30 days before harvest, the parathion residue at harvest time on B i n g cherries, M o r p a r k and Tilton apricots, Yakamines, Italian prunes, Elberta and J . H . Hale peaches ranged from 0.00 to 0.08 p.p.m., as shown i n Table I . When less than 30 days were allowed to elapse between spraying and analysis, the parathion residue on the above soft fruits ranged from 0.30 to 1.63 p.p.m. Increased concentrations of parathion applied to Golden Jubilee peaches resulted i n a higher parathion residue. The amount of parathion residue was roughly proportional to the length of time be tween date of application and date of harvest. Table II. Variety Bartlett pear Bartlett pear D'Anjou pear D'Anjou pear Jonathan apple Delicious apple Winesap apple a
a
α
Parathion Residue on Pears and Apples
North side
South side
0.01 0.02 0.04 0.02 0.02 0.04 0.02
0.00 0.04 0.03 0.00 0.02 0.02 0.03
Area Sampled and Parathion Residue, P . P . M . East West side side Top Average 0.00 0.04 0.04 0.00 0.01 0.01 0.04
0.03 0.00 0.05 0.04 0.01 0.01 0.04
0.01 0.02 0.04 0.00 0.03 0.03 0.04
0.01 0.02 0.04 0.01 0.02 0.02 0.03
Range 0.00 0.00 0.03 0.00 0.01 0.01 0.02
to 0.03 to 0.04 to 0.05 to 0.04 to0.03 to 0.03 to 0.04
Plots sampled twice.
Apples and Pears Single tree plots of Bartlett and D ' A n j o u pears and Jonathan, Delicious, and Winesap apples were sprayed on June 2 and 28 with 1 pound of 2 5 % wettable paraAGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.
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WALKER— PARATHION SPRAY RESIDUE ON SOFT FRUITS, APPLES, AND PEARS
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thion powder and 2 pounds of 5 0 % 2,2-bis-p-chlorophenyl-l,l,l-trichloroethane ( D D T ) . Samples of one full box (1 bushel) were selected from the north, south, east, and west sides and from the top of the tree. These samples were subsampled i n the laboratory and analyzed b y the same procedure as the samples i n Table I . The results are presented i n Table I I .
2
12
22
30
JULY
Figure 1.
Loss of Parathion Residue under Field Conditions
Statistical analysis of the data i n Table I I shows no significant difference between varieties or between positions on the tree. The average parathion residue on a l l varieties is equal to or slightly less than the variation between samples.
Loss of Parathion Residue under Field Conditions Spray programs of 1 and 4 pounds of 2 5 % wettable parathion powder per 100 gallons of water were applied to Delicious apples on July 2 (plots 1 and 2). Samples were taken as soon as the fruit became dry and at 10- to 13-day intervals for a period of 32 days. These plots were sprayed again on August 3 with the same mixtures and resampled over a 30day period (plots 3 and 4). The results and the percentage of loss of parathion are shown in Table I I I and Figure 1. A l l plots lost from 80 to 8 5 % of their parathion residue from the surface of the fruit i n 12 to 13 days and from 93 to 100% i n 30 to 32 days. Plots 3 and 4 were sprayed later i n the season (August 3) than plots 1 and 2 (July 2), and the slightly smaller loss of parathion residue from the surface of the fruits at the later date may be due to a decrease i n volatility of parathion because of lower day and night temperatures.
Relation of Concentration of Spray Mixture to Residue Cover sprays, at concentrations ranging from 0.25 to 4 pounds of the 2 5 % wettable parathion powder per 100 gallons of water, were applied to Delicious apples. These sprays were applied on June 7, J u l y 2, and August 3. The residue samples were selected at harvest time and held i n cold storage (32° F.) for a period of time and then analyzed. The elapsed period of time between spraying and analysis was 90 days. The results are presented i n Table I V . Under normal insect infestations (mites and aphids) encountered i n the state of Washington, a spray program of not more than three cover sprays at a concentration of not more than 0.5 to 1 pound of the 2 5 % wettable powder per 100 gallons of water should give AGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.
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very excellent control of the insects. Normally, a period of 90 days between the last ap plication and harvest would not elapse (45 to 60 days would be expected). The parathion residue at harvest time resulting from a program of 0.5 to 1 pound of 2 5 % wettable powder applied 45 to 60 days before harvest could be expected to be 0.10 p.p.m. or less. The application of sprays with a concentration i n excess of 0.5 to 1 pound (25%) would result i n no measurable increase i n insect control, waste of materials, and higher parathion spray residues. Table III.
Parathion Residue and Rate of Loss under Field Conditions Parathion Residue, P.P.M.
Plot No.
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1°
5.1" 1.0 0.1 0.0
Days between Spraying and Analysis
Loss,
0 12 20 32
0 80 98 100
%
2«
19.1 3.2 1.1 0.8
0 12 20 32
0 83 94 96
36
4.7 0.7 0.4 0.3
0 13 21 30
0 85 91 94
46
18.9 3.5 2.0 1.4
0 13 21 30
0 81 89 93
Sprayed July 1. 6 Sprayed August 3.
a
Table IV.
Relation of Concentration of Spray Mixture to Residue
Plot No.
Concentration", Lb.
Parathion Residue, P.P.M.
1 2 3 4 5 6
4 3 2.56 2 1 0.25
0.60 0.19 0.18 0.18 0.08 0.01
Pounds of 25% wettable parathion powder per 100 gallons of water. 6 Four cover sprays applied June 7 and 23, July 2, and August 3.
α
Parathion Spray Residue on Commercially Sprayed Apples Fifty-five samples of apples—Jonathan, Delicious, Rome Beauty, and Winesap— were collected from commercially sprayed orchards that had received a single parathion spray and where the spray program was known. These samples were analyzed b y the pre viously described method and the results are presented in Table V . Table V.
Parathion Spray Residue on Commercially Sprayed Apples
Spray Program
No. of Samples
Days between Spraying and Analysis
Parathion Residue, P.P.M.
V2 L b . 15% wettable powder/100 gallons water /% Lb. 15% wettable powder/100 gallons water V 4 L b . 15% wettable powder/100 gallons water
29 5 21
32- 81 (av. 55.5) 33- 79 (av. 54.0) 29-78 (av. 51.9)
0.00-0.14 (av. 0.041) 0.00-0.07 (av. 0.010) 0.00-0.07 (av. 0.026)
1
Regression analysis comparing the number of days from spraying to analysis and the parathion spray residue show no significant relationship. The difference i n parathion residue due to the V -, and y - p o u n d applications was not significant. A l l residues were only a fraction of 1 p.p.m. 3
4
AGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.
WALKER—PARATHION
SPRAY RESIDUE ON SOFT FRUITS, APPLES, AND PEARS
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Acknowledgment Appreciation is expressed to W . J . O ' N e i l l and E . W . A n t h o n of the D i v i s i o n of E n t o mology, State College of Washington, for their k i n d assistance i n the field.
Literature Cited
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(1) American Cyanamid Co., Tech. Bull. 2 (1949). (2) Averell, P. R., and Norris, M . V., Anal. Chem., 20, 753 (1948). (3) Washington State College Extension Service, Bull. 279, revised (February 1949),
AGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.
