Soybean planting was a slow process due to the fluctuating temperatures and excessive moisture in many areas. A month ago, while scouting and assessing wheat for stripe rust, I found mature green stink bugs and red-legged grasshoppers. The irony of the situation was that these are generally considered late-season insects. This means that they survived our rather mild winter.
Above: Green Stinkbug
Many pests and threats have arrived early this year. A good example is the early germination of waterhemp. I can only assume that insects are going to be an early problem as well. My weeds professor in college, Dr. George Kapusta, once told us that you need at least two weeks of continuous temperatures at or below freezing to kill 10% of the insect population. Granted—most insects utilize other insects as their food source—but we still have the major concern of those bugs that attack our crops.
Above: Bean Leaf Beetle
While you are out assessing soybean emergence, populations and looking for other abnormalities, you should be looking for insect damage as well. We will have insects that migrate or are blown into our fields and there will be those that overwinter in the field itself. Early-season insect scouting should include roadside ditches, tree lines and waterway edges along with the rest of the field. Some insects will have overwintered in the field while others will be emerging from these protected areas and migrating into the crop fields.
Above: Mexican Bean Beetle
As a general rule, soybeans can tolerate 30-40% defoliation during the vegetative stages and 20% from bloom to pod fill before rescue treatments are warranted. However, these values can vary depending on the infestation level and the type of insect. These values are well defined on a variety of websites and give the Economic Injury Level (EIL) and EconomicThreshold (ET) for most all crop insects. In addition, many insects can transmit important viral diseases that can further reduce soybean yield. Some prime examples of this are: bean leaf beetle/bean pod mottle virus, soybean aphid/soybean mosaic virus, and soybean thrips/soybean vein necrosis virus.
Above: Japanese Beetle
I created my own scouting chart several years ago (below) from a multitude of sources and have adapted it to my geographic region, but it should serve you well for other parts of the state. You will notice a couple of insects on my chart that you might not see normally—you might find damage from seed maggots and wireworms on rare occasions and this year’s cooler, wetter soils appears to be ideal for them. Additionally, I have blister beetles in this chart. While blister beetles normally do not cause large amounts of damage to soybeans, they can be an indicator of a much bigger problem—grasshoppers. The larvae of the blister beetle feeds on grasshopper eggs. Therefore, large swarms of these beetles can indicate a potential grasshopper problem.
Here are a couple of closing thoughts. Consider developing your own Integrated Pest Management (IPM) program on your farm. Unfortunately, generic insecticides are cheap and easy to tank mix when making a POST herbicide or fungicide application. Make sure you need the insecticide before using it. Consult the websites or your CCA/Agronomist for the correct identification, life cycle, EIL’s, ET’s and treatment options should you find insects causing a problem in your fields.
Above: Black Blister Beetle
Finally, when spraying insecticides, please remember the presence of beneficial insects as well, i.e., bees, lady bugs, assassin bugs, wheel bugs, lace wings, ground beetles, etc. They prey on the harmful insects that attack your plants.
Images courtesy of:
Terry Wyciskalla is an independent crop and soils consultant based out of Nashville, Illinois. He specializes in soil sampling, fertility recommendations, precision ag services and crop problem diagnoses. He serves a 12-county area throughout Illinois. He earned his 4R Nutrient Stewardship certification in 2015 and is happy to be a part of the 2016 Soy Envoy team.