University of Minnesota
Fillmore and Houston Counties
Despite the somewhat late start to the planting season, we are seeing soybean aphids and armyworms starting to pop up in southern Minnesota. If you have not already started you should be scouting for these pests. Now with alfalfa weevils still floating around, one might think that we aren’t quite far enough along to be concerned with other pest issues. However, it is the alfalfa weevil that is currently out of its usual timeframe and not the aphids or armyworms. With second cutting started across the state, remember to use your cutting timing to your advantage if you are still seeing alfalfa weevils. Unfortunately, we don’t have such tools for these other two pests.
For soybean aphids, prioritize scouting those fields where you have seen aphids colonize first. These will typically be fields with wooded borders and abundant buckthorn. Also keep an eye out for lady beetles and ants on soybean leaves as both are indicators that aphids may be present. Diligent scouting is necessary to ensure that this pest remains controlled. Remember that the economic threshold is 250 aphids per plant with most plants infested and aphid populations increasing. This threshold will help ensure your application is profitable and that you are not resetting the system unnecessarily. If you are seeing predators such as lady beetles, they may be managing that issue and negating the need to spray. With more limited insecticide options moving forward, we need to be more discerning with those applications to help avoid resistance issues with our remaining insecticides. For more information check out the most recent article on soybean aphids in Minnesota on the Minnesota Crop News Blog.
For armyworms, prioritize areas of dense stands and lodged areas of grass crops. Current reports have it most common in corn planted into a rye cover crop. However, there have been grass hay crops that have been impacted as well. Armyworm larvae are most active at night and in low-light periods. Most of the crop destruction of this pest happens towards the last two instars of its larval development. Warmer temperatures do help development of this pest. Feeding damage and frass are an indication that you have armyworms. Use a sweep net to look for small larvae, in corn look in the whorl and on the soil surface, and in small grains shake the plant and count the ones that fall on the ground. Economic thresholds for whorl stage corn are 25% of the plants with two or more larvae or 75% of the plants with one larva or more. For small grains and grass hay crops use a threshold of 4-5 larvae per square foot. For more information on this year’s armyworm issues, check the recent pest alert article on armyworms in Minnesota from the Minnesota Crop News Blog.
For more information please reach out to your local County Extension office. Residents in Fillmore and Houston counties can email firstname.lastname@example.org or call (507) 765-3896 or (507) 725-5807 for assistance.