Fall flaming effects on densities, distributions, and dispersal of Tetranychus urticae and Neoseiulus fallacis (Acari : Tetranychidae, Phytoseiidae) on peppermint

Fall naming of harvested peppermint, Mentha piperita L., fields for disease control immediately decreased levels of the predatory phytoseiid mite Neos eiulus fallacis (Garman) by 84-98%, while suppressing the spider mite pest Tetranychus urticae Koch to a lesser extent. By the following spring, more T. urticae were found in flamed fields than unnamed fields and in many case s the pest reached outbreak densities (>5 per leaf) and required use of mit icides for control. After harvest on unflamed mint, more N.fallacis were fo und on prostrate plants near the humid soil surface than on erect plants, w hereas spider mites were near equal on prostrate and erect plants. The Ist erect plant type was 15-25 cm tail without leaves on the lower 7.5 cm. The 2nd was 2.5-7.5 cm tall with at least 3 sets of leaves and the prostate pla nts extended to only 1.3 cm above the soil surface. The net effect of this temporal-spatial asynchrony between predators and prey was to uncouple the system, temporarily. This uncoupling for a short time (physiologically) see med to stabilize interactions by keeping the predators from overexploiting spider mite populations in the fall and spring. Tests of selective naming i n small field plots showed that predaceous mites dispersed 7-8 m from unnam ed plots to recolonize named plots before spider mites reached outbreak con ditions. Allowing small, unflamed refuges to exist where predaceous mites c an survive may reduce negative impact of naming on control of spider mites at whole field levels.