Effect of pesticide applications on abundance of European red mite (Acari: Tetranychidae) and tryphlodormus pyri (Acari: Phytoseiidae) in Nova Scotian apple orchards

Pesticide use and mite counts were recorded in 38 apple orchards in 1985 and 46 orchards in 1986. Pesticides were scored on a scale from 1 (harmless) to 4 (harmful) according to their toxicity to the phytoseiid mite Typhlodromus pyri Scheuten. Counts of European red mite, Panonychus ulmi (Koch), were higher in orchards with higher total insecticide scores and more applications of certain insecticides (azinphosmethyl, cypermethrin, deltamethrin, dimethoate, and pirimicarb) and fungicides (benomyl and captan). T. pyri were found in 26% of the orchards surveyed in 1985 and 35% of those surveyed in 1986. Orchards with T. pyri bad higher counts of apple rust mite, Aculus schlechtendali (Nalepa), and were more likely to have had applications of the less toxic insecticides, pirimicarb and azinphosmethyl, than were the other orchards. Orchards with T. pyri also had lower seasonal scores for fungicide toxicity and fewer applications of the acaricidal fungicide, Dikar (a mixture of mancozeb and karathane), or the insecticide phosalone. In orchards with T. pyri, higher counts of the phytoseiid were associated with higher counts of apple rust mite, twospotted spider mite, Tetranychus urticae Koch, and the predacious stigmaeid mite, Zetzellia mali (Ewing) as well as with applications of primicarb, dichlone, and metiram. Counts of T. pyri were reduced by higher total toxicity scores for fungicides and miticides. We conclude that prospects for biological control of European red mite are good if organophosphate-resistant T. pyri are released in uncolonized orchards, and if growers use a modified spray program to promote survival of T. pyri and apple rust mite. The program should include use of dichlone and captan to control apple scab, Venturia inaequalis (Cke.) Wint., primicarb, azinphosmethyl, or phosmet to control insects after bloom, and bacterial/pyrethroid mixtures rather than recommended rates of pyrethoids to control winter moth, Operophtera brumata (L.), and leafrollers.