Management of Summer Populations of European Red Mite (Acari: Tetranychidae) on Apple with Horticultural Oil

Abstract

A highly refined horticultural petroleum oil, Sunspray Ultra Fine, was evaluated in laboratory and field tests for efficacy against summer eggs and larvae of European red mite, Panonychus ulmi (Koch). Oil had significant ovicidal and residual larvicidal activity in dip treatments at rates as low as 0.00005%, but treatments using the same rates in a Potter spray tower caused less mortality. High-contact mortality of mite larvae sprayed in laboratory tests was obtained at rates of 0.25–1.00%. Field applications of oil by airblast sprayer were tested during the summer for their ability to suppress mite populations throughout the growing season. Effective control was achieved with three applications of oil at 3 and 2%, starting at the petal-fall stage and continuing on a 2–3-wk schedule. A rate of 1% provided control under conditions of moderate population pressure but required an additional spray in late July under severe population pressure. Rates of 0.25 and 0.05% resulted in unacceptable mite numbers by midsummer. Phytotoxicity caused by the oil was most severe at the higher rates, but oil caused no leaf drop even when trees were moisture-stressed. No effects of oil were seen on fruit finish or color, except for an increase in scarf skin of ‘Law Rome’ at the highest rates. High-pressure handgun oil sprays against a mixed population of mite eggs, immatures, and adults reduced motile forms by 79–95% at rates of ≥0.25%.