Population Trends of Selected Phytophagous Arthropods and Predators Under Different Pesticide Programs in Virginia Apple Orchards

Abstract

Population trends of selected pests in Virginia apple orchards [ Panonychus ulmi (Koch), Aculus schlechtendali (Nalepa), Aphis citricola Van der Goot, Dysaphis plantaginea (Passerini), Platynota . spp.] and predators [ Leptothrips mali (Fitch), Haplothrips subtilissimus Haliday, Orius insidiosus Say, Stethorus punctum (LeConte), Deraeocoris nebulosus (Uhler), Chrysopa spp.] were monitored during 1977 and 1978 under three reduced-pesticide programs. The pesticide program with phosalone and Dikar® [a blend of Dithane® M-45 (coordination product of zinc ion and manganese ethylene bisdithio=carbamate) and technical Karathane® (2,4-dinitro-6-octylphenyl crotonate, 2,6-dinitro-4 octylphenyl crotonate, and nitro-octyl-phenols)] as its major components allowed the largest number of predators to remain in the orchard and controlled most pests. Platynota spp. caused economic damage during August and September, regardless of the pesticides used or the number of predators in the orchards. L. mali and H. subtilissimus were the most abundant predators and probably responded numerically to densities of A. schlechtendali . The presence of this mite species may aid the development of large numbers of thrips within an apple orchard. O. insidiosus and D. nebulosus usually increased too late in the season to reduce aphid populations, but aphids may be important in attracting these general predators into the orchard. S. punctum ’s response to densities of P. ulmi was inconsistent, but together with other predators it may have had an important role in reducing P. ulmi populations. Chrysopa spp. remained at consistently low levels throughout the study under all pesticide programs.