EFFECTS OF DIFFERENT INTEGRATED PEST-MANAGEMENT PROGRAMS ON BIOLOGICAL-CONTROL OF MITES ON APPLE BY PREDATORY MITES (ACARI) IN NOVA-SCOTIA

For 3 yr (1989-1991) we examined effects of different integrated pest management (IPM) programs on populations of mites in an apple orchard in Nova Scotia, Canada. The stage 1 IPM program involved pest monitoring and application of insecticides (phosmet, pirimicarb, Bacillus thuringiensis var. kurstaki Berliner + one-tenth the recommended rate of cypermethrin) known to be harmless or slightly harmful to the phytoseiid predator Typhlodromus pyri Scheuten. With the stage 2 program, most insecticide applications were replaced by alternatives such as insecticidal soap, insect pathogens, and insect growth regulators. In stage 1 and stage 2 plots, apple scab, Venturia inaequalis (Cke.) Wint., was controlled either with captan, a fungicide that is harmless to phytophagous mites and T. pyri, or with metiram, a fungicide that is slightly harmful to phytophagous mites and moderately harmful to T. pyri. In June and July 1989, densities of European red mite, Panonychus ulmi (Koch), and apple rust mite, Aculus schlechtendali (Nalepa), were too high (maximum 7.6 to >100 per leaf) to be controlled by the low numbers of T. pyri (<0.1 per leaf) present in the orchard. An early August application of the miticide propargite in stage 1 plots or hexythiazox in stage 2 plots caused populations of P. ulmi and A. schlechtendali to decline to 0 per leaf without reducing T. pyri populations. In 1990 and 1991, mite counts in stage 2 plots did not differ with fungicide regime. In stage 1 plots, however, counts of P. ulmi and A. schlechtendali were higher and counts of T. pyri, but not the stigmaeid predator Zetzellia mali (Ewing), were lower with metiram than with captan. Biological control was effective in stage 2 plots and all captan plots: maximum counts of P. ulmi and A. schlechtendali were <1.5 per leaf and 6 per leaf, respectively. Maxima were higher, but still subeconomic, in the stage 1 metiram plots: 5 per leaf for P. ulmi and 9 per leaf for A. schlechtendali. Additive toxic effects of insecticides and fungicides on T. pyri, the possible contribution of Z. mali to biological control despite competition with T. pyri, and recommendations for integrated mite control are discussed.