EFFECTS OF ORCHARD GROUND COVER AND MITE MANAGEMENT OPTIONS ON THE POPULATION-DYNAMICS OF EUROPEAN RED MITE (ACARI, TETRANYCHIDAE) AND AMBLYSEIUS-FALLACIS (ACARI, PHYTOSEIIDAE) IN APPLE

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 overw intering site of A. fallacis was investigated. Two orchard grass treat ments, one mowed and the other unmowed, were compared with clean cultu re. Various treatments for control of P. ulmi were applied when econom ic thresholds were approached or exceeded. Treatments consisted of aca ricides, horticultural oil, and release of predatory mites. Leaf sampl es were taken weekly, and changes in mite population dynamics were rec orded throughout the growing season. The presence of ground cover had little effect on the number of A. fallacis or P. ulmi recovered from l eaf samples in either year of the study. Even though predatory mites d id use the ground cover for overwintering, a large number of A. fallac is were found overwintering directly on the tree. In 1993, two applica tions of horticultural oil resulted in a significantly lower prey-to-p redator ratio than the acaricide treatment. Although the release of pr edatory mites resulted in higher A. fallacis numbers than the acaricid e and horticultural oil treatments, it did not result in a lower prey- to-predator ratio than the untreated and horticultural oil.