Field experiments were conducted in 1992 and 1993 in an apple orchard to evaluate the effects of ground cover and management options on the population dynamics of the European red mite, Panonychus ulmi (Koch), and its predator, Amblyseius fallacis (Garman). In addition, the overwintering site of A. fallacis was investigated. Two orchard grass treatments, one mowed and the other unmowed, were compared with clean culture. Various treatments for control of P. ulmi were applied when economic thresholds were approached or exceeded. Treatments consisted of acaricides, horticultural oil, and release of predatory mites. Leaf samples were taken weekly, and changes in mite population dynamics were recorded throughout the growing season. The presence of ground cover had little effect on the number of A. fallacis or P. ulmi recovered from leaf samples in either year of the study. Even though predatory mites did use the ground cover for overwintering, a large number of A. fallacis were found overwintering directly on the tree. In 1993, two applications of horticultural oil resulted in a significantly lower prey-to-predator ratio than the acaricide treatment. Although the release of predatory mites resulted in higher A. fallacis numbers than the acaricide and horticultural oil treatments, it did not result in a lower prey-to-predator ratio than the untreated and horticultural oil.
