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Soybeans
Volume 58 Number 17 Date 08/29/2013


SOYBEAN APHID - The second half of the annual survey documented the highest densities since 2008. Examination of 139 soybean fields, once in July and again in August, found a state average of 18 aphids per plant during the July survey and a significantly higher count of 55 per plant this month. State average densities from 2010-2012 were extremely low at 7-16 aphids per plant and the state average in 2008 was 72 per plant. Approximately 6% of the sites sampled from August 6-28 contained economic populations of 250-587 per plant, 22% had moderate averages of 50-249 per plant, and 72% had lower counts of less than 49 per plant. Populations in 30% of fields decreased from July to August, suggesting that approximately one-third of the survey sites required aphid control this season.

Many acres of late-planted soybeans now have moderate populations near the 250 aphid per plant threshold. These fields should be evaluated one last time in the next few days since control measures may be justified and foliar treatment is not economical for soybeans beyond the R5.5 growth stage.

GREEN CLOVERWORM - Larvae of various maturities are still causing light defoliation of soybeans in the southern and west-central counties. The damage observed in the past week was minor. Populations have been low since the first larvae appeared in mid-July.

JAPANESE BEETLE - Adults continue to be active and fairly common in soybeans. Defoliation has not exceeded economic thresholds and control has been unjustified for most fields this summer. The heaviest infestations in soybeans were noted in Chippewa, Eau Claire and Monroe counties earlier this month.

-- Krista Hamilton, DATCP Entomologist