There are many management efforts you can take before your soybean seed goes into the ground. Some of these actions are simply insurance and some of them, like your choice of row-spacing and planting date, are the best insect management decision choice you’ll make all year. Unlike corn, which has many yield-robbing seedling pests (i.e., sugarcane beetle, billbugs, grubs, etc.) and the ever-present threat of thrips in cotton, we have very few seedling pests to contend with for soybeans. Also unlike corn and cotton, seed treatments are not economical in North Carolina soybeans. In fact, seed treatments and foliar oversprays have been tested in both Virginia and North Carolina for over 10 years. Across nearly 20 trial/locations, there was not a single yield loss recorded due to seedling pests. These trials were designed with the intent of creating a problem with insects. In one case, thrips numbers were as high as 91 per seedling, a situation that would have killed a cotton plant. There were no yield differences in this trial. The odds are that very very few fields, in our state will benefit by increasing yield from an insecticidal soybean seed treatment. And just as an aside, neonicotinoid seed treatments will not kill kudzu bugs. Read on to learn more about the soybean seedling pest complex.
In Virginia and North Carolina, both thrips and bean leaf beetle are a non-issue in terms of soybean yield when they infest seedlings. Do not scout or treat (or use seed treatments) for either of these pests.
Grasshoppers, katydids, and cutworms tend to be a problem on fields with lots of residue (think no-till) and fields that have not been properly rotated. They are also more of a problem on field edges. These should be controlled with a pyrethroid if they begin to reduce stand levels to densities below those recommended by NC Cooperative Extension (see adjacent graph).
Slugs, which are also more of a problem in no-till fields, are more difficult to control, as insecticides are ineffective. They are more of a problem when conditions are cool and wet which tend to be early on in the season. Slugs are difficult to sample, not only because of their small size, but because they are active in low light conditions, like cloudy days and at night. One thing that you can do is to move the residue around to find the slugs and to look for the slime of their trails where they have moved. The dried slime will shine in the sun.
The best management action to reduce slugs is to till. If you’re producing under no-till, slugs are probably not going to change your tillage practices. Basically the more trash you can clean away from the seedlings, the fewer problems you will have. Consider strip till. Less drastic steps are focusing on good residue removal with the row sweepers and using starter fertilizer.
The only known remedial measure for slugs, besides waiting for warmer and dryer weather, is to use Deadline M-Ps (AMVAC), Orcal Slug Bait and Snail Bait (Orcal). These must be put out with a spreader and are relatively expensive. Furthermore, although this product will likely be labeled for 2013, supplies are short due to reregistration. If you might use one of these products this year, you’ll want to pick up what you can now.
Three-cornered alfalfa hoppers feed on seedling and are generally discovered after the fact, when plants lodge later in the season. Seed treatments and foliar pyrethroid sprays can effectively manage these insects. The problem is that it takes EXTREMELY high densities to impact yield. So your money is wasted 99.9% of the time targeting a seed treatment for these critters. See this previous blog post for more information and this website for the threshold. In short, if you’ve had a problem with these in the past, do not waste your money with a seed treatment. Scout your beans and treat if you need to.
Finally, lesser cornstalk borer can give us problems, especially in late-planted soybeans, on droughty soils, and/or during hot and dry periods. Unfortunately we do not know of any remedial control measure (including pesticides) that is effective for this insect. This previous blog post contains information concerning varieties that are more of less resistant to this insect.