Phytoseiid mites on peppermint and effectiveness of Neoseiulus fallacis to control Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae) in arid growing regions.

The humid-adapted species Neoseiulus fallacis (German) was the most common phytoseiid mite collected in either humid (> 100 cm annual rainfall) or arid (20-45 cm annual rainfall) mint growing regions of Washington, Oregon, Montana, Idaho, and California during 1991-1995. In experimental field plots, this predator gave excellent biological control of Tetranychus urticae Koch on mint grown under arid conditions in central Oregon when evaluated by an insecticide check method or by the caging of mites. N. fallacis is effective as a predator in arid areas probably because regular irrigation creates a humid environment in the canopy. The selective miticide propargite, when used in combination with predators, was effective at reducing high spider mite populations to below the treatment threshold faster than did N. fallacis alone.