Scout Fields for Soybean Insects to Protect Current and Future Yield Potential

By Harmon Wilts

Soybean insects can have a serious impact on soybean yield potential, not only during the current season but also in future years. Three of the top soybean pests are soybean cyst nematodes, spider mites and soybean aphids. Scouting your fields during the growing season is an important step to help protect plant health and yield potential. 

Soybean Cyst Nematodes

Female soybean cyst nematodes (SCN) burrow into and suck moisture from the roots, resulting in reduced water and nutrient uptake available to the plant. The number of nitrogen-producing nodules formed on the roots can also be reduced. Common symptoms include plants turning yellow and/or shortened plant height. To confirm the presence of SCN, farmers should dig up roots and look for small, round egg sacs. Later in the season, those eggs will drop and hatch in the soil, where they can infest the next soybean crop. In my area of Minnesota, in fact, they can remain dormant for up to 10 years. Use of seed treatments or selecting SCN-resistant soybean varieties are two lines of defense, but there is no remedy once the plants are infested.  

Spider Mites 

These microscopic insects are commonly found during hot, dry weather. They attach to the underside of plant leaves and suck contents out of leaf cells, turning plants yellow or tan, stunting their development and robbing yield potential. An effective scouting method is to hold a white piece of paper under the leaves and shake the plant. Swipe any black dots that appear on the paper with your hand — the presence of moisture will confirm they are spider mites. These insects can be controlled with insecticides, but they can reduce yield potential quickly, so it’s important to stay on top of managing this pest.

Soybean Aphids

Like spider mites, soybean aphids tend to have a larger impact during dry conditions. These small, greenish insects feed on the underside of new plant growth, piercing and sucking moisture from the leaves as well as from stems. Indications of infestation include stunting of plants, yellowing leaves and sooty mold, which causes a charcoal-gray leaf discoloration. Aphid populations should be monitored the most closely during pre-productive growth stages, when they can cause the most serious damage to yield potential. The University of Minnesota Extension recommends a spraying economic threshold as an average of 250 aphids per plant on more than 80% of the examined plants.* 

For additional information, contact your DEKALB® Asgrow® brand dealer or technical agronomist, or check local university extension resources.

*University of Minnesota Extension. Minnesota Crop News. Reminders for soybean aphid management: scouting, thresholds and insecticide selection. July 21, 2020.

Harmon Wilts is a DEKALB Asgrow technical agronomist serving West Central Minnesota. 

ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields. 

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