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 Neoseiulus 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 cases the pest reached outbreak densities (>5 per leaf) and required use of miticides for control. After harvest on unflamed mint, more N.fallacis were found on prostrate plants near the humid soil surface than on erect plants, whereas 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 plants 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) seemed to stabilize interactions by keeping the predators from overexploiting spider mite populations in the fall and spring. Tests of selective naming in small field plots showed that predaceous mites dispersed 7-8 m from unnamed plots to recolonize named plots before spider mites reached outbreak conditions. Allowing small, unflamed refuges to exist where predaceous mites can survive may reduce negative impact of naming on control of spider mites at whole field levels.