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Insect control in soybeans hinges on knowing the pest and good timing

Pest control in soybean fields takes a more active role from growers and crop consultants than managing corn. That’s not to say scouting for corn insects is not necessary—we still have cutworms to deal with in most years. There are occasional secondary pests, and we have to be vigilant to fend off resistance to Bt traits and seed-applied insecticides. However, corn-insect management has mainly consisted of adding a pyrethroid to our pre-emerge herbicide and letting the seed treatment and the transgenic traits do the rest. At the expense of soybean yield, this attitude often carries over to soybean production. Unfortunately, if growers take this laissez-faire attitude toward pest control in soybeans, it’s likely that the soybeans will take a laissez-faire approach to yield. In the current commodity price environment, each bushel counts.

Insecticide seed treatments have become a standard operating procedure for soybean growers, and a valuable tool for early-season protection. Most commonly, these treatments are controlling below ground pests that will effect stands, along with first-generation bean leaf beetles. Bean leaf beetles not only threaten the leaves and cotyledons of soybean seedlings but can vector soybean diseases such as bean pod mottle virus. In more northern geographies where soybean aphids tend to show up earlier, seed treatments can do an excellent job of controlling early infestations. However, several caterpillar pests can still be a threat early, and later infestations of aphids and bean leaf beetles can still threaten treated soybean fields.

Late season control of insect pests in soybean production takes a much more hands-on approach. To ensure season-long control, there is no substitute for scouting. Without understanding the insect population in your field, the growth stage of the crop, and the current weather pattern, an insecticide program will not be effective.

When it comes to mid- and late-season scouting, there are a couple categories of insects to consider. The first is foliar-feeding insects and sucking insects. The second is pod-feeding insects. Foliar damage is the most noticeable plant damage and the easiest to scout for, but the least damaging. Soybean plants excel at replacing leaves if damage comes during periods of rapid vegetative growth. The most vulnerable periods are during seedling stages when insects could overwhelm small plants, and reproductive stages when vegetative growth slows. Economic thresholds at seedling and reproductive stages are around 25 percent defoliation, but can be as high 50 percent during vegetative stages.

It is important to keep these thresholds in mind when treating foliar feeding insects. A treatment for these pests can prove valuable, but may also have unintended effects. Unless you use the right product, you may increase pressure from sucking pests, specifically aphids and spider mites. Both of these pests are subject to control by beneficial insects, which are affected by insecticide treatments. The best strategy is to use products that will control both aphids and mites. Such dual control is particularly helpful in hot, dry conditions where spider mites thrive. Products like Hero which contain bifenthrin help a great deal on mites. Lorsban is a good tank mix partner with bifenthrin for mite control along with adding to aphid knockdown. Any of the neonicotinoid insecticides will provide excellent residual control of aphids.

Of course, pod-feeding insects such as podworms, stinkbugs, and even bean leaf beetles are consistently the most dangerous pests to soybeans. Little damage from these pests is needed to justify treatment, and frankly, it is rare that there is not a combination of pod-feeding insects at high enough levels to treat. Since pod feeders are present the majority of the time, applying an insecticide at pod set is a good practice.

It is still important to scout. Knowing the species of insect present is critical for good control. Caterpillars, stinkbugs, and beetles, for example, all behave differently. They are best controlled by specific products. Each pest may require different rates of insecticide for control and may or may not be affected by residual control.

To ensure proper timing and product selection, scouting for threat levels is imperative. The difficulty is scouting properly and knowing how and when to look for these pests. An extra set of eyes from a consultant in a program like MFA’s Crop-Trak can help. We’ve seen good results with Crop-Trak weekly field inspections and recommendations. Communication among this network of consultants has proven that understanding emerging threats and proactive approach to control makes an effective insect control program.

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