Field surveys across the southern half of Wisconsin indicate that the most advanced soybeans are at the R5 beginning seed growth stage and soybean aphid pressure has generally been low. This is according to the Department of Agriculture, Trade and Consumer Protection.
Of the 168 sites surveyed as of July 31, only two fields had an average count exceeding 25 aphids per plant. The highest count recorded was 76 aphids per plant on 84 percent of the plants, in Waushara County.
The vast majority of soybeans scouted by DATCP for economic pests this month have had infestations in the range of 1-20 aphids per plant on less than 50 percent of the plants throughout the field. In addition, natural enemies such as ladybeetle larvae, green lacewings, and parasitoids are abundant in many fields.
Soybean aphid populations often increase rapidly from late July to early August, and scouting and insecticide treatment decision-making will be most critical in the next two weeks.
To qualify for treatment, a soybean field must meet the following three criteria:
- The average aphid count is greater than 250 soybean aphids per plant
- More than 80 percent of plants are infested with soybean aphids
- The population is increasing
Additionally, growers should evaluate soybeans for two-spotted spider mites and defoliation caused by Japanese beetles, green cloverworms, and assorted caterpillars. Defoliation that meets the 20 percent threshold between the bloom and pod-fill stages and 30 percent in the pre-bloom stages may warrant control. For accurate assessment, scout several areas in the field interior, in addition to field edges.
