How to Tackle Insect Pests in Corn, Soybeans This Season

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These five tactics can help customers deal with yield-robbing bugs

When customers call with questions about pest management and ask what they should be scouting for, the correct answer most likely is "watch for everything." Of course, it's also the first rule in scouting: see what's present and develop a plan of action.

But your customers are facing another year of challenges as 2021 dishes out crazy weather, so what's the best approach this year? Discuss these five key tactics with customers to help them get on track for the rest of this growing season.

1. Weather matters.

In any given season, weather varies widely across the country. Help customers understand how conditions beyond the amount of rainfall can be an early warning to pests they might face. A good example of weather impact is with soybean aphid and spider mites in both corn and soybeans.

"One of the bigger things on soybeans coming up this season is soybean aphid," says Bryan Jensen, extension entomologist, University of Wisconsin. "We've seen that some states have already found them. It's early, but I like to do a little spot checking in fields to get a feel for what's happening."

Jensen notes that under the hot weather that hit the Midwest early in the growing season, he's not expecting to see a huge population increase in those aphids – this pest does not like hot weather. But if conditions change, "they can bounce back pretty quick."

If weather remains hot and dry, there's another pest that can raise a challenge. Spider mites can hit both corn and soybeans. "Warm, dry weather can set the stage for all of this, I'm not sounding an alarm but that's something to look for," he says.

2. Scouting pays.

When discussing scouting with an entomologist, they're talking about a thorough walk through a field taking a closer look at crops. While a pickup truck spot check may sound good, problems can develop in fields beyond your view. As more dealers turn to drones and other aerial imagery tools to manage crops, it can help target scouting efforts for greater efficiency too.

Customers know that scouting is about counting bugs or measuring damage. Seeing stress in the field earlier either with timely scouting or imagery can be an added service for customers working to maximize yield. And that's more important in a year where crop prices have ballooned.

"The crop is more valuable [this year]," says Christian Krupke, extension entomologist, Purdue University. "Farmers' willingness to pay to keep risk low may be higher. Scouting is key to that."

"The crop is more valuable [this year]. Farmers' willingness to pay to keep risk low may be higher. Scouting is key to that."
-Christian Krupke


3. Managing treatment investment.

If a customer identifies a pest in the field, the next step is to determine if they need to treat. When combating insects there's a fine line to walk regarding when to treat and when to walk away. Rising commodity prices mean those per-bushel yield losses are dearer and may justify treatment.

Wisconsin's Jensen notes, however, that for each pest every state has its own guidelines for when to treat. These are available from state extension resources. For example, the timing of black cutworm injury may be different in one state versus another. Helping customers understand the right treatment time or options is a business opportunity.

Jensen says Wisconsin farmers were seeing black cutworm damage in their crop early this season, as well as some true armyworm injury. The key is to assay the level of damage and the populations you're dealing with.

In Indiana, for example, black cutworm can have up to three generations, and your chances of having a problem depends on other risk factors including tillage and crop rotation. Yet treatment may be advised if primary leaf feeding tops 3 to 5%, and you find two or more cutworms per 100 plants.

For soybean aphids, Purdue's Krupke says the treatment threshold is common across the Midwest – if you see 250 aphids per plant it's time to treat. "That threshold is used throughout the region and it's worked for years," he says.

For those spider mites, which can hit quickly in hot weather, the field edges will show damage early. The treatment threshold depends on timing. "Once we get into drought in corn, we will see spider mites start to move into the field from the edges," Krupke says. "But a good rain will cure spider mites for nothing."

4. Understanding treatment options.

Economic threshold is a phrase most farmers have heard more than once. It's that financial balancing act for determining when to pull the trigger on a treatment for an in-season pest. As noted earlier, this can vary by state for some pests. But another factor that enters the economic threshold conversation is efficacy.

Just spraying a problem could be money down the drain if timing, or the treatment approach, isn't tackled using best practices. There are treatments for black cutworm, aphids and spider mites.

Just spraying a problem could be money down the drain if timing, or the treatment approach, isn't tackled using best practices.


Yet timing for spider mites, if the problem arises due to continued drought, is that treatment options kill adult and immature mites, but do little to eggs already laid. "The insecticides we apply don't kill anything in the egg," says Wayne Ohnesorg, extension educator and entomologist, University of Nebraska. "It's not unusual to need a retreatment 10 to 14 days later depending on how severe the infestation was before you treated. This is a pest you have to watch closely."

Helping customers match their treatment timing to the pest infestation, and understand the potential for follow-up will be important for best results.

5. Looking for new pests.

Soybean gall midge is starting to emerge," says Ohnesorg. This is a pest that first appeared in Nebraska in 2011, and for now there are few treatment options. Entomologists are still learning about the pest, but for now it can't be stopped with seed treatments, and insecticide sprays have not been thoroughly tested for efficacy.

Scouting can help identify if fields are infested. Entomologists recommend scouting starting at V2 in soybeans. The pest has been identified in Nebraska, Iowa, Minnesota, Missouri, and South Dakota. This is a pest to put on your radar when sending scouts to the field.

For the 2021 season, watching for everything makes sense, and given higher crop prices spending time with a trusted adviser offers more value to the customer. This is an opportunity to help the customer reevaluate economic treatment options, which can help preserve income.

This content produced by Farm Progress for Corteva Agriscience.