Check your Fields this Week! Soybean aphid populations continue to increase in the region. The MN Department of Ag pest survey from July 27 to Aug 2 shows that fields were reaching levels where some plants exceeded 1000 aphids/plant (Figure 1). For a regional perspective, check Thursday’s issue at the web site provided.

 http://www.mda.state.mn.us/pestsurvey/PestReports/PestReport.html

Fields that were in the 50 to 100 aphids per plant last week are reaching the 250 aphids per plant level this week. Decisions are still being made on a field by field basis. Reports vary from populations still below threshold, neighboring fields above threshold, some fields where populations declined from last week, and of course others with populations increasing.

A big factor that will start to determine decisions is Soybean Growth Stage (see Issue 10).

R5 Beginning seed – Seed 1/8" long in a pod at one of the four uppermost nodes on the main stem with a fully developed leaf. We continue to use a treatment threshold of 250 aphids/plant when population is actively increasing. Remember, positive yield response from treating at this stage is less predictable and significantly less than economic infestations that are reached during R1 to R4.

R6 Full seed – Pod containing a green seed that fills the pod cavity at one of the four uppermost nodes on the main stem with a fully developed leaf. We will have many fields at this stage by next week. Research trials throughout the north central states have not demonstrated a yield benefit to treating soybean for aphid management at the R6 and beyond stages.