Absence of mowing prevents resurgence of Tetranychus urticae and Panonychus ulmi (Acari: Tetranychidae) after broad-spec
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ORIGINAL RESEARCH PAPER
Absence of mowing prevents resurgence of Tetranychus urticae and Panonychus ulmi (Acari: Tetranychidae) after broad‑spectrum insecticide use in apple orchards Ken Funayama1 · Michiyo Komatsu1 Received: 17 March 2020 / Accepted: 28 June 2020 © The Japanese Society of Applied Entomology and Zoology 2020
Abstract We investigated whether mowing the undergrowth in apple orchards affects the occurrence of spider mites and their predators, phytoseiid mites. We compared their occurrence between one unmown and one mown plot in an apple orchard in Akita Prefecture, northern Japan. Neither plot was mown in 2014 or 2015, but one plot was mown monthly from late May to late August in 2016 and 2017. Both plots were sprayed with narrow-spectrum insecticides in 2014 and 2015 and broad-spectrum insecticides in 2016 and 2017. In 2014 and 2015, some Tetranychus urticae were present on leaves in both plots, but their numbers did not increase greatly. In 2016, numbers of Panonychus ulmi and T. urticae surged in the mown plot, but grew slightly in the early growing season and then decreased in the unmown plot in association with rapid population increases of the predacious mites Typhlodromus vulgaris and Neoseiulus womersleyi. In 2017 also, numbers of T. urticae surged in the mown plot but remained low in the unmown plot. In addition, the numbers of T. vulgaris until July were significantly greater in the unmown plot in both years. Moreover, the population density of T. urticae when N. womersleyi began to appear was significantly lower in the unmown plot in both years. These results suggest that the resurgence of spider mites can be avoided by not mowing in apple orchards. Keywords Neoseiulus womersleyi · Panonychus ulmi · Resurgence · Tetranychus urticae · Typhlodromus vulgaris · Mowing
Introduction The principal spider mite species of apple orchards in Japan are the two-spotted spider mite, Tetranychus urticae Koch, and the European red mite, Panonychus ulmi (Koch) (Toyoshima 2003). Among them, T. urticae is the most difficult to control, because it has developed resistance to many acaricides (Funayama 2010). As a consequence, annual outbreaks of T. urticae occur in many orchards. Tetranychus urticae has a wide host range that includes various plants in the undergrowth of orchards (Gotoh 1997). Many apple growers have traditionally considered the undergrowth to be a source of T. urticae, which has resulted in the frequent mowing of their orchards. Despite this practice, the density
* Ken Funayama [email protected] 1
Akita Fruit-Tree Experiment Station, Yokote, Akita 013‑0102, Japan
of T. urticae on apple trees generally increases in commercial apple orchards each summer (Funayama 2010). By contrast, we previously found that retaining the undergrowth suppressed T. urticae populations in apple orchards managed with narrow-spectrum insecticides, concluding that the vegetation provides habitat for the native predatory phytoseiid mites, Amblyseius tsugawai Ehara, Typhlodromus vulgaris Ehara, and
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