Pest Roundup

Rust, Aphids and Worms, Oh My

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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Southern corn rust is among the many pests to scout for this week. The disease has moved as far north as Nebraska and Iowa in record time this year. (Photo courtesy Bob Kemerait of University of Georgia Extension.)

ROCKVILLE, Md. (DTN) -- It may not be your best corn and soybean crop, but to the pests of the world, it's still a feast in waiting.

In the insect world, the western corn rootworm is having a decent rebound season, after rainy hatch periods helped suppress populations the past two years. Soybean aphids with resistance to pyrethroid insecticides have also surfaced once again in the upper Midwest.

In the meantime, an aggressive fungal disease -- southern corn rust -- is making itself at home in Midwest cornfields in record time.

Scouting will be of the utmost importance for these pests and many more that will visit corn and soybean fields. Here's the latest on each:


The timing of a new disease-tracking website for southern corn rust couldn't have been better.

"We picked the year to do it with southern corn rust moving so quickly into the I-states," University of Kentucky Plant Pathologist Carl Bradley said. "This is definitely a new thing for some of these [Midwestern] growers to deal with."

The disease, which usually doesn't breach the Midwest until August when corn yields are safe, moves far faster and can do much more damage than its mild-mannered relative, common rust. So far, it has been found as far north as Nebraska, Iowa and Illinois.

See the map here:…

Use the growth stage of your corn and the weather forecast as your guide for spraying for the disease, which does not have an established threshold for treatment.

It loves hot, humid weather, Bradley said.

"If you're in areas getting pretty frequent rainfall and you're finding rust in corn at the milk stage or before, you should really consider a fungicide application," he said.

If you find the disease, take a sample and send it a diagnostic lab. Alert your local Extension agent of any positive findings, so they can help document the spread. Remember also to tweet rust and other disease findings to @corndisease on Twitter (or @soydisease for soybeans).

For more help with treatment decisions, see this guide from the University of Kentucky:…

For a table on effective fungicides, see this table:…


Growers in the upper Midwest should get used to scouting for insecticide-resistant soybean aphids.

For the third year in a row, University of Minnesota has confirmed populations of the pest that can survive applications of pyrethroid insecticides, according to a university news release authored by four Extension scientists.

See the release here:…

The resistant populations seem to be concentrated in the Southwest regions of the state, although they have been found in northwest Minnesota this year, and in 2016 as well.

Neighboring states, such as North Dakota, are encouraging growers to scout the following insecticide applications and alert Extension agents to any suspicious aphid populations.

See the North Dakota alert here:…

For help scouting for aphids, use this Minnesota guide:…

See this guide for more information on resistance management:…


The rootworm does most of its damage underground. But in late July and early August, farmers have a chance to evaluate its damage through root digs and adult beetle scouting, according to university entomologists.

University of Wisconsin Entomologist Bryan Jensen is urging growers to dig roots now to check the effectiveness of Bt traits or soil insecticides. If you wait too long, you risk the root tissue regenerating and masking the injury, Jensen warned in a university news release.

See the release here:…

Examining corn roots is a messy business -- use this guide on digging and measuring damage from Nebraska here:…

Jensen's article also contains a video on how to scout for adult rootworm beetles, which can give you valuable information about next year's populations. In severe infestations, spraying for adult beetles might be warranted, added University of Nebraska Entomologist Robert Wright.

Wright has published a table showing what levels of beetle populations in a corn crop might be worth treating, as well as information on the timing of the application.

See the table here:…

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Emily Unglesbee