February 1942 V y ^ n^, E-558 AGRICULTURE BUREAU Of ENTOMOLOGY AHO rtANT QUA«AMTIHE DICHLOROETHYL ETHER FOR THE CONTROL OF THE PLUM CURCULIO ON PEACH By Oliver I. Snapp, Division of Fruit Insect Investigations Lead arsenate, the insecticide at present generally used for the effective control of the plum curculio ( Conocrachelus nenupha r Herbst) on peach, has an injurious effect on the foliage, buds, budwood, and fruit of peach trees under certain conditions. Injury caused by lead arsenate to buds, budwood, or fruit directly reduces the peach crop, while the damage to foliage may bring about premature defoliation, which interferes with the proper nourishment of the fruit buds for the following season's crop and, in cases of heavy defoliation, produces premature fall blooming. Because of these objectionable features, investigations have been carried on at the Fort Valley, Ga. , laboratory to develop a suitable and effective sub- stitute for lead arsenate in the control of this insect. To eliminate the use of an insecticide on the trees, treatment of the soil under the spread of peach trees to kill the plum curculio in the larval and pupal stages has been included in these investigations for a number of years. Preliminary laboratory experiments with dichloroethyl ether were included in this phase of the project in 1937, and more extensive experiments with this material in the laboratory, in connection with caged peach tree, and in commercial peach orchards, were conducted during the seasons of 1938 to 1941, inclusive. The purpose of this circular is to report briefly on the favorable results of these experiments and to make the information pertaining to the use of dichloroethyl ether available to any who may want to try it for the control of the plum curculio attacking peaches. Results of Experiments In laboratory experiments dichloroethyl ether, used at the rate of 1/3 fluid ounce in 1/6 gallon of water (1/6 gallon of 1.5-percent emulsion) per square yard of soil, was found to be effective against plum curculio larvae, and that material at the rate of 1 fluid ounce in 1/6 gallon of water (1/6 gallon of 4.5-percent emulsion) was found to be effective against - 2 - plum curculio pupae. During the season of 1939 only 1 plum curculio adult emerged from 3 caged peach trees, each of which had been artificially infested with approximately 465 curculio larvae, in addition to those that fell from these trees, before the soil under each tree received 2 applications of dichloroethyl ether — one at the rate of 1/3 fluid ounce in 1/3 gallon of water per square yard of soil when most of the insects were present as larvae, and one at the rate of 1 fluid ounce in 1 gallon of water per square yard of soil when most of the insects were in the pupal stage. The next year only 4 curculio adults emerged from 4 caged trees, each of which had been artificially infested with approximately 350 plum curculio larvae, in addition to those that fell from these trees, before the soil under each tree received only 1 application of dichloroethyl ether at the rate of 1 fluid ounce in 1/6 gallon of water (1/6 gallon of 4.5-percent emulsion) plus 0.2 percent of sulfated alcohol per square yard of soil. In 1941 a total of only 13 plum curculio adults emerged from 4 caged peach trees, each of which had been artificially infested with approximately 883 plum curculio larvae, in addition to those that fell from these trees, before the soil under each tree was sprayed with 1/6 gallon of 1.5-percent dichloroethyl ether emulsion per square yard of soil, chiefly against the larvae, and with 1/6 gallon of 4.5-percent dichloroethyl ether emulsion per square yard of soil, chiefly against the pupae. In extensive experiments conducted in a commercial peach orchard during the season of 1941, a program consisting of two applications of dichloroethyl ether on the soil under the spread of the trees, together with 12 jarrings to catch overwintered adults, gave as good control of the plum curculio as the regular schedule of lead arsenate sprays on the trees. The first application of dichloroethyl ether was at the rate of 1/6 gallon of 1.5-percent emulsion per square yard of soil directed chiefly against the curculio larvae, and the second application was at the rate of 1/6 gallon of 4.5-percent emulsion per square yard of soil directed chiefly against the pupae. No injury to vegetation under the spread of the peach trees or to any part of the trees or foliage could be discerned from the two applications of dichloroethyl ether on the soil, whereas trees that had received the regular schedule of lead arsenate were from 90 to 95 percent defoliated on September 12, following an especially favorable season for arsenical injury. Description and Properties of Dichloroethyl Ether Dichloroethyl ether, C4H8CI2O, is a colorless liquid with an ether- like odor. It is soluble to the extent of 1.02 percent by weight in water at 20° C. (68° F.). which is equivalent to 1/10 of a gallon of dichloroethyl ether dissolved in 12 gallons of water. It is extremely resistant to hy- drolysis and is soluble in practically all oils and organic solvents. Dichloroethyl ether has a boiling point of 178.5° C. (353.3° F.), a flash point of 185° F., and a vapor pressure at 20° C. of only 1.2 mm. It is therefore not very volatile. The molecular weight of dichloroethyl ether is 142.98. and its vapors are about five and a half times as heavy as air The specific gravity of dichloroethyl ether (20/20° C.) is 1.2219. It weighs 10.2 pounds per gallon and has been selling for 17 cents a pound in 55-gallon drums or 20 cents a pound in 5-gallon lots. Preparing Stock Emulsion of Dichloroethyl Ether To avoid the breathing of undue concentrations of the vapor, the emulsion should be prepared outdoors or in a well-ventilated room. It is desirable that the air temperature be between 50° and 80° F. The stock emulsion is prepared as follows: First stir 9 parts by volume of dichloro- ethyl ether i nto 1 part by volume of potash fish-oil soap. A good grade of potash fish-oil soap should be used, that is, one without an excess of caustic potash and containing approximately 30 percent of soap and 70 percent of water. Place the 1 part of potash fish-oil soap in a container and work the 9 parts of dichloroethyl ether into the soap by constant stirring. Start by adding a very small quantity of the dichloroethyl ether to the soap and completely stir this in before making another ad- dition. The ether should be added at intervals and each portion completely worked into the soap before another is added, until the 9 parts of ether have been worked into the 1 part of soap. When the fish-oil soap and dichloroethyl ether have been thoroughly emulsified, add water slowly with constant stirring until the emulsion measures twice the volume of dichloroethyl ether used. For example, if 18 gallons of the emulsion are desired, start with 1 gallon of potash fish-oil soap, to which add slowly at intervals, with constant stirring, 9 gallons of dichloroethyl ether. Then add water, as directed, until the total quantity measures 18 gallons. This is the stock emulsion and contains 50 percent of di- chloroethyl ether. The stock emulsion is diluted with water before use, the amount of dilution depending on the stage of the insect against which it is used, as is discussed later. If the stock emulsion breaks down after preparation, this will be indicated by the appearance of globules of dichloroethyl ether at the bottom, or by a curdled mass or a layer of clear dichloroethyl ether at the bottom, that cannot be readily remixed by moderate agitation. If this occurs, the material must be re-emulsified. This can be done by pumping the mixture from one container to another or back into the same container, or by starting over again with a small quantity of potash fish-oil soap to which small quantities of the broken-down emulsion are added slowly at intervals with constant stirring. Dilution Table 1 gives the quantity of water to be added to the 50-percent stock emulsion of dichloroethyl ether to make 100 gallons of diluted emul- sion of the strengths found by experiments to be most satisfactory for use against plum curculio larvae and pupae in the soil under the spread of peach trees. ^^.. UBRARY ^ATE PLANT BOARD UNIVERSITY OF FLORIDA lllliiil Table 1. — Dilution of stock emulsion of dichloroethyl ether and strength of diluted emulsion for use against plum curculio larvae and pupae in the soil. For use against — Quantity required to make 100 gallons of diluted emulsion Strength of the diluted emulsion Water 50- -percent stock emulsion Larvae Pupae Gallons 97 91 Gallons 3 9 Percent 1.5 4.5 When and How to Apply the Emulsion The first application should be made after all the larvae have left the fallen peach drops and entered the soil. This is usually some time during the first 15 days of May at Fort Valley in central Georgia. A 1.5- percent emulsion should be used for the first spray and it should be applied under the spread of the trees at the rate of 1/6 gallon per square yard of soil. For peach trees in Georgia this will be at the rate of about 1-1/2 gallons for small trees, 2 gallons for medium-size trees, and 3 gallons for large trees. The second application should be made when most of the insects are in the pupal stage, which would be about 2 weeks after the time of the first application. A 4.5-percent emulsion should be used for the second spray and it should be applied under the spread of the trees at the same rate as that for the first spray. The overwintered plum curculio adults should be caught by jarring in the spring, when dichloroethyl ether is to be used as a substitute for lead arsenate for the control of the plum curculio attacking peaches. However, it will not be necessary to pick up peach drops when the ether is used, and this will offset the expense of jarring for the overwintered curculios.