As soybeans begin to emerge, get out in the field to evaluate your soybean plant populations. You'll want to keep an eye out for both above-ground pests and explore those that live beneath the soil surface.
Generally speaking, a stand of 125,000 to 145,000 soybean plants per acre has the potential achieve maximum yields. When you are out scouting and looking closely at soybean stands, be sure to examine any skips (no evidence of a seed or seedling) found in your rows and determine the reason why no seedlings exist in those areas.
If you don’t have a planter issue, and poor seedling vigor and soil crusting have been eliminated as the cause, then you should consider insects and disease as the likely culprit. Even though most soybeans have been treated with a fungicide, disease can still occur when certain conditions exist.
When rotten soybean seed is found in the soil with no insect presence, chances are good that it may be from disease. Both phytophthora and rhizoctonia like wet and warm soils, while pythium prefers wet and cool soils. In some of these situations, replanting could be necessary.
Subsurface insect pests that can cause a soybean stand reduction include wireworms, seedcorn maggots and white grubs. There are no rescue treatments for subsurface insects, so you may wind up replanting soybeans and using insecticide-treated seed, or using an in-furrow insecticide.
Before replanting be sure to check with your crop insurance provider about any provisions that may impact your replanting decision for soybeans or corn.
Above ground insects that feed on soybean seedlings include bean leaf beetles (BLB), stink bugs and grasshoppers. BLB attack the first planted fields the hardest, making holes in the leaf’s surface. BLB like to hide on the underside of soybean leaves when they are disturbed, which makes them difficult to see and find. Stink bugs, however, can be found anywhere on the plant, and grasshoppers tend to be found on field borders and feed primarily on leaf margins.
Each of these insects can be treated once their feeding reaches the correct treatment level, based on the the insecticide labeled for use on soybeans that you choose. Various treatments of these insects are typically based on the defoliation of the soybean seedlings—50 percent defoliation is a common level to begin insect control, but always read and follow label use directions.
Be diligent with scouting your soybean crop—once a week should ensure no disease or insect problem will impact your final yields. We've put together a guide for getting the most out of your chemical applications which might be helpful - take a look.