By Seth Naeve, Ph.D.
University of Minnesota agronomist

Don’t Ignore Your Fields
“August Makes Beans” represents an old adage, but there remain a number of important management decisions to be made on most farms. Pest control during seed filling remains crucial to maximizing soybean yields. Any stresses placed on the plant during this period translate directly to yield losses. Multiple pests or any pest at high-incidence levels can impact yields in a measurable way. As soybean crops begin to fill seed, a tendency exists to walk away from soybean fields and let Mother Nature do her thing, but this can be a mistake. Now’s the time to scout for weeds, insects and diseases.

Weeds
Most soybean farmers have made their last application of herbicides by late July. August is a perfect time to scout for weeds not controlled by previous herbicide applications. Farmers should use this time to determine whether these weeds may have escaped by emerging after the last pass of herbicide or whether they are tolerant or actually resistant to the herbicides used. While glyphosate tolerant weeds may impact this year’s crop, their impact will certainly grow in the future. Removing these weeds before they produce viable seed will reduce their impact on future crops. Use of an alternate herbicide may still be an option for many farmers this season. Identifying these weeds now will allow farmers to make better crop and herbicide choices in future years.

Insects
Insect infestation and damage shows up most prominently in August. Soybean aphid populations often spike this month. Aphid colonies that have remained at low levels throughout June can easily increase rapidly and impact soybean yields. Although frequent rains have reduced aphid population pressure, farmers need to keep an eye on these populations. Populations that have reached 250 aphids per plant and are on the rise should be scheduled for eradication. It’s also important to scout for defoliating insects like Japanese beetles in August. Defoliators cause the most injury to the soybean plant and reduce yields most during the month of August. Keep a close eye on Japanese beetles and spray when defoliation reaches 20 percent. Timely spraying becomes even more critical as we reach the R5 and R6 growth stage when new leaves are no longer produced and seed filling begins in earnest.

Diseases
Scouting soybean fields for diseases remains critical during August. The Midwest has experienced a nearly ideal season for the development of several major soybean diseases. Farmers may find diseases this year they have not seen previously. Farmers should identify soybean diseases for mid-season and future management decisions. Identifying soybean diseases helps determine fungicide applications this year and provides information for subsequent year decisions, such as variety selection and seed treatment options. Foliar applications of fungicides are unlikely to provide an economic return to farmers in the absence of foliar diseases. Likewise, fungicide seed treatments are unlikely to provide value to farmers when appropriate root-rotting fungi are not present.
Even if farmers have made their last pass of glyphosate or sprayed an insecticide, it is still a good time to get out to scout soybean fields. Scout them one by one and take good notes. Farmers who scout their fields now will be glad they did next year.

posted by Expert 2:50 pm