(1959) W. C. Pierce,
Entomology Research Division, Agricultural Research Service, U. S. Department of Agriculture
Organic-phosphorus insecticides were compared in orchard experiments in northwestern Louisiana during the years 1955-57 to determine their effectiveness against first-generation larvae of the pecan nut Casebearer, Acrobasis caryae Grote. Earlier work has shown the effectiveness of properly timed spray applications of parathion and EPN against that pest. Further, in a preliminary test in 1954 Malathion and methyl parathion were about as effective as parathion against a light infestation. The treatments were applied to singletree plots randomized within blocks replicated six or more times. Trees of the Stuart variety were used in 1955 and 1956 and those of the Desirable variety in 1957. Applications were made with a conventional hydraulic sprayer equipped with a hand gun after first-generation eggs on pecan nuts had begun to hatch in large numbers and before many of the larvae had entered the nuts. Infestation records were obtained near the end of the feeding period (late June) by examining 100 clusters of nuts on each tree. The materials tested and the results obtained are given in Table 1. Under conditions of severe infestation in 1955, parathion was more effective than methyl parathion, malathion, or Diazinon. In a separate test carried out under the same conditions in an adjoining area of the orchard, EPN, 2 pounds of a 25-percent wettable powder per 100 gallons, more effective than any of the foregoing materials. In 1956 EPN, Guthion, and Malathion gave very good control. Observations on nearby untreated trees indicated that only 26 percent of the nuts were infested. It is probale that the light infestation was partly responsible for the favorable showing of the test treatments, since such infestations are not difficult to control. In 1957 Guthion was superior to malathion under a heavy infestation. First-generation larvae destroyed about 52 percent of the nuts on untreated growing near the test plots. It is concluded that each of the insecticides can be expected to control first-generation larvae provided adequate quantities are applied at the proper time. Best results can be expected when the treatments are made after the eggs have begun to hatch in large numbers and the larvae have started to attack pecan buds and nuts. The pecan nut casebearer can be controlled with dusts and with semi concentrate (2x) sprays applied with air-blast equipment as well as with dilute sprays applied with hand guns. From 400 to 500 gallons is the amount of dilute spray we have found necessary to spray an Here of large pecan trees adequately. In general, good control has been obtained with 50 pounds of 2-percent or 40 pounds of 10-percent malathion duet per acre applied either with ground mandatory or aerial equipment shortly after the larvae began to attack the nuts. Good result have also been obtained against the fruit-generation larvae with adequate quantities of a 2x concentrate spray of either parathion or malathion applied with an air-blast sprayer. The results with aerial applications of concentrated insecticide spray have not been satisfactory. Aerial applications of parathion. 1 pound, or DDT, 2 pounds, plus parathion, 1 pound, in 5 gallons of spray per acre have not given adequate control. More detailed studies of aerial applications are in order, particularly to determine the value of increasing the strength and volume of spray applied per acre. Each grower should select the insecticide and method of application most suitable for his particular situation, such as the degree of infestation, type of spray equipment available, occurrence of other pests requiring control at the same time, and materials than are smallest to handle. When it is necessary to bein spray applications very easily in the period in which eggs are deposited, DDT should be used in combination with the phosphorus insecticide of choice. This will improve the residual value of the treatment.