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Southern university entomologists offer suggestions to keep corn insect problems from blowing up

SUGARCANE BEETLES are increasingly a pest of corn in some areas          mdashMississippi Crops photo
<p><em>SUGARCANE BEETLES are increasingly a pest of corn in some areas. </em><em>&mdash;Mississippi Crops photo</em></p>
Growers need to take advantage of the different Bt technologies for optimum insect control and resistance management. They can match the technological trait with the insect problem they have, and often can use hybrids with multiple Bt traits for the same pest, which can help with resistance management.

Louisiana’s biggest corn pest is the soil insect complex, including wireworms that are more severe in cool, wet seasons when plants grow slowly.

“In years of heavy, early rains, we need to bump the insecticide seed treatment to the 1,250 rate, especially for controlling pests such as sugarcane beetles,” says Louisiana State University Entomologist David Kerns, Winnsboro. “Most years, we can get by with the 500 rate. 

“Outside of these soil pest problems, transgenic corn does a great job of controlling caterpillars. We still have to watch for cutworms, which some of the transgenics don’t pick up as well as other Bt hybrids. In refuge corn, caterpillar control is a whole different ballgame.

“In the last few years, I’ve seen more sugarcane borers than southwest corn borers,” says Kerns, referring to the acres of non-Bt corn farmers must plant as part of their resistance management plan. “Sugarcane borers are easy to overlook until they blow up on you.”

Soil insect complex

The No. 1 insect pest that Mississippi corn growers deal with is the whole soil insect complex, including wireworms, white grubs, rootworms, sugarcane beetles.

“We address this insect complex on every acre with seed treatments at various rates,” says Angus Catchot, Mississippi Extension entomologist, Starkville. 

“We’re studying new options that complement the seed treatments, such as in-furrow granular and spray insecticides. We pick up incremental yield as we add those products, particularly in continuous corn and no-till production.

“The two above ground insects we normally deal with are stink bugs, and on non-Bt acres, southwestern corn borer.

“The dual-gene Bt corn hybrids do a really good job of keeping caterpillar pests out of the whorl stage; we rarely measure any yield loss even when we see earworms feed on the tips.”

Effective and economic insect control in corn production relies heavily on selecting the appropriate Bt corn hybrid and using the correct insecticide seed treatment rate.

“After growers consider a hybrid’s agronomics — high yield potential, area adaptation and disease package — they select the Bt technology traits that best fits the insect conditions in their area,” says Auburn University Entomologist Kathy Flanders. 

Higher rate may be needed

A higher insecticide seed treatment rate may be needed in situations that increase the risk of insects attacking seedling corn.

“The standard rates of 250 or 500 (0.250 or 0.500 milligrams of active ingredient per kernel) sometimes don’t adequately control several of our tough early season pests,” Flanders says.

“We recommend growers order the 1,250 rate (1.25 mg a.i./kernel) in situations such as farming new ground, planting continuous corn, or in a heavy cover crop.

“In general no-till, growers could probably still use the 250 or 500 rates. However, we recommend they burn down the cover crop, leaving nothing on the field for a month before planting.

“In no-till, there’s quite a lot of wheat cover that harbors cutworms. Growers can also apply a low rate of a pyrethroid insecticide to control the pest at planting.”

Matching hybrids, seed treatments

A major decision for Tennessee corn growers is matching hybrids with insecticide seed treatments.

“For example, growers should consider using a higher seed-treatment rate if they are putting a CRP field or a pasture into production,” says Scott Stewart, Extension entomologist, Jackson.

“They might also want to use the higher rate when planting corn in fields with a history of sugarcane beetle. Or they can use an in-furrow treatment such as bifenthrin, Capture or Brigade, in addition to the standard treatment that comes on the seed.

“We also need to take advantage of the different Bt technologies for optimum insect control and resistance management.

“Growers can match the technological trait with the insect problem they have, and often can use hybrids with multiple Bt traits for the same pest, which can help with resistance management,” Stewart says.

Western corn rootworm

“For example, a few areas of the state have Western corn rootworm problems, particularly where continuous corn is grown. Growers can use multiple Bt technologies very well in such a situation.”

Arkansas’s soil insects, including wireworms, chinch bugs and white grubs, normally are controlled adequately with an insecticide seed treatment applied at the 250 rate.

“In 2014, however, stink bugs were an even bigger problem in seedling corn than they were in 2013,” says University of Arkansas Entomologist Glenn Studebaker, Keiser. 

Part of the problem is that some growers are starting to use cover crops, such as field peas, which can build up stink bug populations over the winter.

“The standard seed treatment rate doesn’t do much for stink bugs,” Studebaker says. “The higher 1,250 rate does a better job of suppressing stink bugs for a while.

Scout for fall armyworms

The 500 rate is preferred in problem fields with a history of wireworms or other soil insects, a field that has been fallow for several years, or pasture that’s conducive to wireworms.

“In refuge corn, we urge growers to scout closely for fall armyworms, as well as southwestern corn borers. We recommend treating threshold levels with a good residual material, such as Belt, Prevathon, Besiege or Intrepid.” 

Fall armyworms were a problem in some of South Carolina’s late-planted corn in 2014, and in grain sorghum. It is expected to be problematic in some areas of the state in 2015.

“The best way to control fall armyworms in corn is to plant hybrids with the correct Bt trait,” says Entomologist Francis Reay-Jones, Clemson University Pee Dee Research and Extension Center, Florence. 

“We have some very good Bt technology to control fall armyworms. Growers can choose from several Bt traits to control worm pests — such as fall armyworm and corn earworms — that are common in their area. Early season, we focus on soil insect pests, including sugarcane beetles, which we usually have more frequently in the western part of the state.

“Once you have sugarcane beetles, it’s too late, so you need to order a higher insecticide seed treatment rate or use soil insecticides.”

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