Volume 65 Number 17 Date 08/27/2020
SOYBEAN APHID - Populations recorded during the annual survey were mostly low. Only 4% of the 179 fields sampled from July 20-August 21 had moderate populations of 101-163 aphids per plant, 5% had 51-100 per plant, and 91% had fewer than 50 aphids per plant. The 2020 state average count was just 15 aphids per plant, with no surveyed fields showing above-threshold populations of 250 aphids per plant. For comparison, the 2019 survey found a record-low average of five aphids per plant, the 2018 average was 14 aphids per plant, and surveys from 2010-2017 documented average counts of 6-55 aphids per plant. Although reports indicate that some fields developed economic populations of >250 aphids per plant this season, DATCP's survey results suggest that aphid control was generally not required for most soybean acres in 2020. Nearly all of the state's soybean crop has now matured beyond the growth stage (R 5.5) where treatment is economically worthwhile.
JAPANESE BEETLE - Defoliation has been observed in 80% of the 179 soybean fields sampled by DATCP since late July. Counts recorded during the annual aphid survey ranged from 1-138 beetles per 100 sweeps, with a state average of 17 per 100 sweeps (14 per 100 sweeps in 2019). The highest counts of 100 or more beetles per 100 sweeps were observed in Clark, Crawford, and Lafayette counties. Although beetles are still apparent in crops, orchards and residential areas, much of their activity should decline within the next two weeks.
TWO-SPOTTED SPIDER MITE - Leaf stippling and bronzing symptoms have intensified in some western Wisconsin fields with this month's dry weather pattern. Scouting for mites is suggested for one more week. Treatment of this pest is only beneficial prior to the R5 to R5.5 or full pod growth stages.
-- Krista Hamilton, DATCP Entomologist