Be on the Lookout for these Insects

April 5, 2010 07:00 PM

Weather produced a lot of misery for corn growers in 2009, but where insects were concerned Mother Nature cut them some slack. Bug problems for most farmers were modest, thanks to weather and resistant hybrids.

"Late corn planting and cool temperatures created a limited window for corn insects to be active,” explains Purdue University's Christian Krupke. "The corn crop was under very little drought stress, which is when you tend to see rootworm damage. Corn rootworms are always around, but their impact is greater if you have drought during or after the insects' feeding period.”

"With the ever-expanding use of Bt hybrids, we are not seeing as many problems with southwestern corn borer or European corn borer,” says Ric Bessin of the University of Kentucky.
Although there were few major insect outbreaks in 2009, there are lessons to be applied to insect management in 2010. Here's what entomologists are telling farmers this spring.

Western bean cutworm.
"Growers need to be watching for western bean cutworm, which is a new pest in this area,” Purdue's Krupke says. "There were some fairly high damage levels this past year in northwestern Indiana counties.”

Western bean cutworm originated in the Great Plains and has been spreading into the Corn Belt. In recent years, it has been found in Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, North Dakota, Ohio, South Dakota and Wisconsin. Yield losses as high as 40% have been recorded in Colorado, where high populations were left untreated. Losses are lower, but still significant, in the Corn Belt.

"We haven't found any infestations of western bean cutworm in Ohio yet, but we are scouting for it,” says Ohio State University's Ron Hammond. "Last season, we caught close to 600 adults in traps—about five or six times as many as we did in previous years. We also saw our first caterpillar—but it was only one. We found no infestations of larvae.”

Emerging pests. Entomologists are watching what some of them call emerging pests—insects that are not major threats but might become significant in the future because they are not controlled by resistant hybrids.

"Japanese beetle is a newer field-crop pest in Iowa,” says Erin Hodgson of Iowa State University. "I'm encouraging growers in the eastern part of the state to be on the lookout for early signs of silk clipping.”

Just across the state line into Illinois, Japanese beetle densities were high in corn fields in 2009, notes Mike Gray of the University of Illinois.

In Iowa, Hodgson is spreading the word about extended diapause in northern corn rootworm, which has led to damage in some first-year corn. "Although the variant strains are at low numbers, it's important to monitor corn for damage to avoid future economic loss,” she says.

In several states, entomologists are keeping an eye on corn leaf aphids. "Last year was the second year in a row that we've had problems with aphids in corn,” says University of Minnesota's Ken Ostlie.

"I think we may have to deal with aphids in the future,” cautions Mike Catangui of South Dakota State University. "Fortunately, there are a lot of insecticides to choose from.”
Normally, aphids are sprayed at tasselling stage, using an airplane or a high-clearance ground applicator, Catangui explains. But this past year in Nebraska, aphids showed up after corn had pollinated, says Bob Wright of the University of Nebraska.

"That may have been because of cool temperatures during July,” Wright says. "The insects were not present on a large number of acres, but some fields were heavily infested. When
they are abundant, aphids can cause economic loss.”

In Minnesota, Ostlie plans to launch research to determine if there is any benefit to spraying aphids after pollination. "We don't have much information on what to do with large populations of aphids after pollination,” he says.

Iowa State University's Hodgson suggests farmers scout for aphids just before corn tassels. "The insects will be protected in the whorl during that time,” she says. "But eventually they will move out to the leaf, ear and stalk. Take note of sticky honeydew or black sooty mold, which may develop on the plant and interfere with grain fill.”

Bird cherry-oat aphids and English grain aphids also have been observed occasionally feeding on corn—the former in Nebraska, the latter in South Dakota and both in Ohio. The insects normally feed on small grains.

"In South Dakota, other insects that qualify as emerging corn pests include sap beetles and adult corn rootworms,” Catangui says.

On the lookout. No one can predict insect outbreaks because so much is influenced by weather. But there are things you can do to make sure bugs don't catch you by surprise.
"Despite all our seed treatments and genetic engineering technology, growers still need to scout their fields to make sure some insect doesn't slip through the cracks,” Bessin says. "In Kentucky, farmers should scout for stink bugs, which attack corn seedlings, and for corn aphids. Those insects hit only sporadically, but they can be serious on occasion.”

Don't forget about secondary pests that are not controlled by resistant hybrids. "In Kentucky, some areas have high levels of wireworms. If a field has had wireworm problems, plant it last. Warmer soil leads to faster germination and growth, which reduces the amount of damage. Seed treatments and soil insecticides can provide protection,” Bessin adds.

In western Nebraska, South Dakota and Kansas, be alert for grasshoppers. "USDA data showed high populations of grasshoppers in those areas last fall, so potentially there are a lot of eggs waiting to hatch,” Wright says. "The weather will determine how many of the eggs survive; a cool, wet spring will decrease the survival rate.

"We can't say what insects will show up this year,” Wright sums up. "Even with our hybrid technology, there's always something to watch for.”

Watch for Cutworms in Weedy Fields
Black cutworms are almost always present, but whether they become a problem depends on the season.

"Cutworm moths come up every year, so cutworms are always a possibility,” says Ohio State University Extension entomologist Ron Hammond. "They become more of a threat anytime you have weedy fields and late planting.”

No-till growers understand that and do their best to manage winter annual weed growth so cutworm moths won't find an appealing spot to lay eggs, Hammond adds. Conventional farmers remove the weed threat with tillage.

Because of the wet fall and late harvest in 2009, farmers in many parts of the Corn Belt have found it difficult to control winter annual weeds this year. And by now, early flying moths may have had time to lay eggs.

"One good thing about cutworms is that they are easy to scout for,” Hammond says. "Thresholds for treatment are well established, and most foliar insecticides that are labeled for the pest do a good job of control. The fields you need to scout are those that have had cutworm problems before and those that had weeds growing prior to planting.”

You can e-mail Darrell Smith at

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