Influence of mowing on dynamics of native phytoseiid mites and Tetranychus urticae in apple orchards in northern Japan.

To support practical integrated pest management in commercial apple orchards, I investigated the influence of mowing on the occurrence of Tetranychus urticae and native phytoseiid mites in apple orchards sprayed with selective insecticides in Akita Prefecture, northern Japan, from 2013 to 2015. The orchards were not mown in 2013, and unmown and mown plots were compared in 2014 and 2015. There were significantly fewer Typhlodromus vulgaris on apple leaves and Amblyseius tsugawai in the undergrowth in mown plots than in unmown plots in both years. Conversely, there were significantly more T. urticae on leaves and undergrowth in mown plots than in unmown plots. The reason for the decreased populations of these phytoseiid mites may be a lack of food (pollen) needed for reproduction on apple trees and in the undergrowth due to mowing. These results indicate that mowing strongly influences generalist phytoseiid mites in apple orchards. Moreover, mowing might increase the density of T. urticae in apple trees because increased nitrogen in the leaves increases fecundity; in addition, drought might promote the increase of mite numbers. Thus, retention of undergrowth suppresses T. urticae in apple orchards.