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Shifting Hosts
 
What To Expect & How To Manage Insect Pests
That Migrate From Corn To Cotton

By Carroll Smith
Senior Writer


As corn acres continue to increase across the Mid-South, researchers are taking a close look at insect populations and developing strategies to control them as they migrate from cornfields into cotton.

According to Roger Leonard, LSU AgCenter research entomologist, planting cornfields adjacent to cotton fields creates a crop interface that influences the dynamics of cotton IPM. Field corn is usually sprayed relatively few times for insect pests, but most cotton fields receive relatively intense spraying.

Field corn is a good host for several insect pests that like to feast on cotton plants. For example, a complex of stinkbugs produced in cornfields and left unmanaged will migrate into cotton as the corn begins to mature. This scenario can play out with tarnished plant bugs and other pests as well.

Acreage Numbers Play A Role

“Another consideration is to think in terms of regional acres of corn,” Leonard says. “A highly mobile pest like the adult stage of corn earworm – or bollworm – that we have in cotton, uses field corn as its primary host in June. When corn acres go up, the potential for infestations in cotton later during the season increase as well. The Louisiana entomologist points out that the move from conventional cotton to Bt cotton technologies significantly re-duced the number of sprays for bollworms and essentially eliminated sprays for tobacco budworm.

“With stacked Bt genes, such as Bollgard II and WideStrike in commercial cotton varieties, the potential bollworm threat was further reduced, but neither one of these technologies should be considered immune from corn earworm,” Leonard cautions. “I consider it relatively uncommon for consultants to treat bollworm in Bollgard II or WideStrike varieties as often as one might need to treat Bollgard varieties. However, if cotton plants experience some form of stress, and optimum Bt protein production is compromised, then corn earworm may get a foothold in those fields and occasional oversprays could be required. Remember, the larger the larvae, the more Bt protein that is required to cause (bollworm) mortality.”

The solution is simple. Scout diligently and apply supplemental control when needed.

Spider Mites Increasing Earlier

Mississippi State University research entomologist Jeff Gore’s first recommendation to thwart such pests as plant bugs, two-spotted spider mites, bollworms and fall armyworms is to plant cotton in as large a block as possible to keep it away from corn in the area to minimize the numbers of corn-cotton borders. Secondly, make additional insecticide applications to the borders of cotton fields adjacent to corn or other plant bug hosts between whole field sprays when insects are migrating into cotton.

Gore points out that 10 years ago, the two-spotted spider mite was considered a late season pest that arrived as cotton was approaching cutout. Lately, he’s seen a big increase in spider mites earlier in the season. The increase in corn acres is not the only cause for the increase in spider mite importance, but it may increase the risk of early season infestations.

“Also, when it’s hot and dry, spider mites will be worse,” he says. “In mid-July when the corn is drying down, mites begin to move out of corn. It’s not something we see in every field, but the risk is definitely there next to any cornfield. To control mites at this time of the season, we recommend using the true miticides, such as Zephyr, Oberon, Comite and others.”

Contact Carroll Smith at (901) 767-4020 or csmith@onegrower.com.

 


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