December 1945 w-076
United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
CONTROLLING THE PEACHTREE BORER WITH PROPYLENE DICHLORIDE EMULSION
Ey Oliver I. Snapp, Division of Fruit Insect Investigations
Experiments conducted during the last 5 years in central Georgia and 1 year at Beltsville, Md., have shown that propylene dichloride emulsion has a number of distinct advantages over ethylene dichloride emulsion and paradichlorobenzene for the control of the peachtree borer (Sanninoidea exitiosa (Say)). On various dry and wet soils it has given excellent control of this insect without tree injury when used at one-half the recommended strength of ethylene dichloride, and, as these materials cost approximately the same oer pound, the propylene dichloride treatment is the cheaper. Propylene dichloride emulsion, like the emulsion of ethylene dichloride, is effective at low soil temperatures and can therefore be used late in the fall and early in the spring, when it is too cold to use oaradichlorobenzene effectively. It is safer around young trees, easier to apply, and more effective than paradichlorobenzene. Furthermore, the propylene dichloride treatment requires a minimum of preparation of the soil before application and no attention subsequent to mounding after treatment.
Pronylene dichloride is a clear, colorless liquid with an odor
similar to that of ethylene dichloride. According to information furnished by the manufacturer, it boils at 95.40 C. (203.70 F.), freezes at -700 C. (-940 F.), has a specific gravity at 250/250 C. of 1.159, and, like ethylene dichloride, is inflammable. It is very soluble in alcohol or ether at 250 C., but its solubility in water is only 0.27 gram oer 100 grams of water at 200 C.; however, it is fairly sta0le in the presence of water. One gallon of the compound at 250 C. weighs
9.64 pounds. No harmful results should be feared in working with propylene dichloride unless it is breathed at high concentrations over a protracted period.
Preparing Propylene Dichloride Emulsion
To avoid concentration of the vapor and any prolonged breathing of it, the emulsion should be prepared out of doors or in a wellventilated room. It is desirable that the air temperature be between 500 and 800 F. Since the compound boils at temperatures below the boiling point of water, heat should not be employed in making the emulsion, and the liquid should be kept away from fire and oen-flame lights. Propylene dichloride is somewhat more difficult to emulsify
than ethylene dichloride; however, a suitable stock emulsion can be prepared by stirring 8 parts by volume of the compound into 1 part by volume of a good grade of potash fish-oil soap- that is, one without an excess of caustic -Potash and containing approximately 30 percent of olid material and 70 percent of water. To make the emulsion, place the notash fish-oil soap in a container and add the propylene dichl~oride slowly at intervals, stirring constantly. When the propylene dichloride is thoroughly emulsified with the soap, add water slowly with constant stirring until the emulsion measures 2 parts for each part of propylene dichloride used. The stock emulsion will then contain 50 percent of propylene dichloride. The stock emulsion should be diluted with water before use, the amount of dilution depending upon the age of the tree and the dosage required (table 1).
Table 1.- Dilution of stock emulsion, strength of diluted emulsion,
and quantity recommended for trees of different ages
Quantity to make 10
Age of :gallons of diluted :Strength of Diluted
trees :emulsion :diluted :emulsion for
(years) :*emulsion :each tree
Gallons Gallons Percent Pint
4 2 10 1/2
3 8 1/2 1 1/2 7.5 1/2
2 8 1/2 1 1/2 7.51/
1 9 1 5 1/8
If the stock emulsion breaks down after nreparation, which will be indicated by the presence of a curdled mass, or a layer of clear pronylene dichiloride on the bottom of the container, and if it cannot bereadily remixed by moderate agitation, the material must be reemulsified. This is done by numnping the mixture from one container to another and back into the same container, or-by starting over again with a small quantity of p~otash fish-oil soap to which small quantities of the broken-down emulsion are added slowly at intervals with constant stirring.
Dilution and Dosage
'fable 1 gives the quantity of water to be added to the 5-percent stock emulsion of -orooylene dichloride to get 1.0 gallons of diluted emulsion of the different strengths aid dosages found by-experiment to be most satisfactory for use around neach trees of various ages.
When ard How to Aprly the Emulsion
Propoylene dichloride emulsion can be anolied for the control of the peachtree borer any time during the fall or spring. Best results will probably be obtained in the fall soon after the close of the egglaying period of the moths, when most of the borers are small. The material should not be anolied to waterlogged, heavy soil late in the fall, since it is more likely to cause injury under these conditions.
No oreparation of the soil before treatment is necessary on loose, level ground, except to raise the soil level wherever there are signs of borers in the tree above the normal ground line. In some cases, however, cupping the soil slightly toward the tree trunk or breaking the crust of hard soil to prevent the liquid from running off, or loosening the soil around the trees sufficiently to permit the liquid to be readily absorbed will give better results. Any cracks in the ground around or extending out from the tree trunk should be filled with soil before the treatment is applied, in order that undue concentration of the material on any part of the root system, which might result in injury, may be avoided.
The material is applied by pouring it on the soil around the base of the tree in such a way that the soil will absorb and hold it around the tree at the ground line. It should not be poured on or allowed to run against the trunk. A tin household measuring cup holding one-half pint, with marks for one-eighth and one-fourth pint, will be found useful for applying the emulsion. It is essential that a uniform mixture be obtained, both in the stock emulsion and in the fully diluted spray. The stock emulsion should be thoroughly stirred before any of it is taken from the container for dilution, and the diluted emulsion should likewise be agitated before each dose is withdrawn for use around the tree. Each bucket of diluted emulsion should be provided with a paddle for a-itation. The operator should examine the emulsions at frequent intervals to be certain that they have not troken down, permitting the propylene dichloride to form a separate layer at the bottom of the container. Broken-down ewulsions should not be applied, as they are less effective against the borer and the portion consisting chiefly of proylene dichloride may cause serious injury to the tree.
After the emulsion has been applied, sufficient soil should be placed on it to reduce surface evaporation of the chemical. After this the treatment needs no further attention.
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