What to Watch: Corn, Soy and Wheat Pests

It’s early July. Are your crops planted? Check. Weeds killed? Check. Bugs under control? Well, in a perfect world, you wouldn’t have to worry about insects in this year’s wheat, corn or soybeans. Crop rotation, seed treatments and/or genetic advancements would have them under control and battling with insects over your crop would be the least of your concerns.

At the time of this writing, we don’t know what the insect pressure will be like later on. What we can do, however, is look at what we think are the most important insects for you to watch for in each of three key crops: corn, soybeans and wheat. If you aren’t scouting for them now, you should be looking soon.

A Threat to Soybeans: Soybean AphidsA Threat to Soybeans: Soybean Aphids

A threat no longer limited to the Midwest, soybean aphids began gaining a foothold in the Plains and Upper Midwest in recent years. Many armchair entomologists predict 2014 will be a year of light soybean aphid pressure, as this pest tends to be less common in even-numbered years. The truth is that no one can accurately predict if the bugs will be more damaging one year versus another. The best way to prepare for soybean aphids is to scout and be familiar with the appropriate economic thresholds.

If you find any fields that have soybean aphids above the economic threshold, an application of a product such as Leverage 360® insecticide can help you control the pests before they begin to affect soybean yield.

A New Resistance: Corn Rootworm (CRW)

Four states — Nebraska, Iowa, Illinois and Wisconsin — are now confirmed to have western corn rootworm resistant to certain Bt toxins, meaning Bt hybrids are no longer effective in certain areas. But confirmation doesn’t mean resistant CRW is limited to these states. Since as early as 2012, states such as South Dakota have been reporting evidence of resistance.

If scouting turns up adult beetles that are above the economic threshold, you’ll want to consider a foliar application of a product such as Baythroid® XL insecticide. The intent is to control the adult female beetles before they have an opportunity to lay eggs.

The scouting process for CRW is a little more complex than that for soybean aphids, but we highlight some scouting tips, and the University of Nebraska provides more detailed information on how to scout for CRW and economic thresholds.

Aphids in Wheat

Aphids don’t typically overwinter in northern wheat-producing areas of the country, blowing in from warmer climates in the spring. Greenbug, bird cherry oat and English grain aphid tend to cause most of the aphid damage to wheat. Infestation typically occurs sometime from the point of stem elongation through heading, with the greatest threat between the vegetative to boot stages. This is because the only major factor aphids can affect after heading is seed weight. According to North Dakota State University, aphids can’t sustain levels high enough to affect weight significantly. 

A number of beneficial insects can help control aphids in wheat. When these insects, such as lady beetles, are present in large numbers, an insecticide probably isn’t necessary. If beneficial insects aren’t at high enough levels and the crop hasn’t yet reached the heading stage, you can consider applying Baythroid XL.

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North Dakota State University reviews the best management practices for corn rootworm.


Earlier this year, Dakota Farmer looked at whether stacked crop rotations can confuse insects and weeds.


South Dakota State University discusses how the loss of crop diversity allows insects and other pests to increase to harmful levels.


Corn and soybean prices might be lower now than when this article appeared in Minnesota Farm Guide, yet growers still continue to favor increasing corn and soybean production while decreasing wheat. Dale Hildebrandt makes a case for why wheat needs to remain part of the equation.


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