Effect of Strawberry Plant Physiological Status on the Translaminar Activity of Avermectin B1 and Its Efficacy Against the Twospotted Spider Mite (Acari: Tetranychidae)

Abstract

Plant physiological status determines translaminar movement of avermectin B1 in strawberry leaves, and the resulting noncontact residual kill of twospotted spider mite, Tetranychus urticae Koch. Significant T. urticae mortality was obtained upon contact with avermectin B1 with and without the addition of dormant oil, and with propargite. Noncontact residual kill of T. urticae by avermectin B1 was greater on fruiting summer-type plants than on plants in winter semidormancy. When avermectin B1 was applied only to the top surface of leaves, addition of dormant oil enhanced T. urticae mortality on lower leaf surfaces of plants in winter semidormancy. T. urticae mortality was not affected by the addition of oil when plants were in either a spring-type vegetative growth state or a summer-type sexual state. The results of this study suggest an explanation for inconsistencies observed in field applications of avermectin B1 for control of T. urticae.