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Soybeans
Volume 61 Number 13 Date 07/28/2016


SOYBEAN APHID - Observations from the annual aphid survey currently underway suggest populations are increasing but remain low for late July. Only three of the 49 fields sampled as of July 27 had an average count greater than 25 aphids per plant on 100% of the plants: one in La Crosse County, one in Outagamie County, and another in Trempealeau County. Aphid counts on individual plants in the margins of those fields ranged from 300-580 per plant. All other surveyed fields had extremely low averages of less than 10 aphids per plant. Soybean aphids can reproduce rapidly under the moderately warm weather pattern predicted for the last days of July, with the greatest population growth occurring at temperatures of 70-80°F. Insecticide treatment, if required, is most effective when applied during the full bloom to full pod (R2-R4) stages.

JAPANESE BEETLE - Light to moderate defoliation is widespread in soybeans, though treatment has not been justified for any field sampled so far this season. The economic threshold for Japanese beetle and other leaf feeding soybean pests is 20% defoliation between bloom and pod fill.

WHITEFLY - Minor infestations were observed this week in soybeans in the west-central counties. Whiteflies are a common pest of greenhouse plants and commercial vegetables, with high reproductive potential and known resistance to several insecticides. Their sporadic appearance in Wisconsin soybeans is primarily a curiosity since yield reductions have never been documented.

OBLIQUEBANDED LEAFROLLER - Most of the larval population observed in the state's soybeans throughout July has pupated. Adult moths should begin emerging by early August.

GREEN CLOVERWORM - Larvae are appearing in southern and western Wisconsin soybean fields. Numbers are still low and defoliation is light (<5% fieldwide), but outbreaks of this caterpillar occur every 5-6 years and conditions are favorable for damaging populations to develop this season.

-- Krista Hamilton, DATCP Entomologist