SW corn borer Pioneer
Larvae of southwestern corn borer: winter (diapause) phase (top) and summer phase (bottom)

The 2017 Corn Insect Outlook

Here are key preplant decisions to help determine grower success with their corn crop.

Using the correct insecticide seed treatment rate and selecting the appropriate Bt corn hybrid for local needs are two key preplant decisions to help determine grower success with the crop.

Generally, for seed treatment in high risk situations that include using minimum tillage, planting continuous corn, planting in heavy cover crop, or farming new ground, growers may want to consider upping the standard seed treatment rate.

Louisiana Pest Spectrum

Pioneer

Cutworms can reduce stands and yield if not managed carefully.

Most of Louisiana’s corn acreage is planted to Bt hybrids, which simplifies insect control tremendously, says Louisiana State University Entomologist David Kerns at Winnsboro. “Transgenic corn has dramatically decreased the issue of controlling pests through the season.

“On refuge corn this past season, I thought we would have problems with sugarcane borers, and perhaps southwestern corn borers, particularly with late corn. But they never became an issue. I think there’s so much Bt corn that it has suppressed those pests.”

Growers also need to handle the soil insect complex with a seed treatment and/or in-furrow insecticide application, he advises. Louisiana experienced a lot of cutworm issues in 2016, and Kerns urges growers to watch out for them again in 2017.

“Many growers rely on in-furrow insecticide applications, which work. The best way to prevent cutworms is to make sure you burn down three to four weeks before planting. That destroys their host crop.

“The big emphasis on planting cover crops to control resistant weeds has complicated insect control. There’s an increased insect population, particularly when growers just row and plant. In those situations, you definitely want to bump the insecticide seed treatment from the standard 250 rate to at least the 500 rate.”

More Arkansas Corn

Conventional corn acreage has expanded in Arkansas, partly due to a local poultry producer who markets chickens fed non-GMO grain, and who pays growers a premium for conventional corn. About 10,000-plus acres of conventional corn was planted in northeast Arkansas, and more non-Bt corn acreage was planted elsewhere in the state.

“Conventional corn brings us back to insect pests we used to fight before we planted Bt corn,” says University of Arkansas Entomologist Glenn Studebaker at Keiser. “The No. 1 pests in conventional corn are borers: southwestern corn borer and European corn borer, with southwestern the more damaging of the two.

“There are several tactics growers can use to manage corn borers — planting early and/or making a preventive insecticide application if borer moths are present. We recommend growers do not make an automatic application for corn borers; that saves money and it’s just good IPM. Instead, we recommend they put out pheromone traps, watch for moth flights, and treat if necessary ahead of egg lay.

“Trapping helps determine the need to spray because the pest doesn’t move a lot — they’re not like bollworm moths, which fly long distances. When growers need to treat, we recommend a residual insecticide such as Prevathon, Besiege, or Intrepid that can last two to three weeks.”    

More growers are planting cover crops to help control herbicide-resistant weeds, Studebaker notes. “It provides better weed control, but can sometimes result in increased insect populations, especially for clover, vetch, or winter peas, which can increase the incidence of cutworms and other insects.

“We recommend when growers plant corn into a cover crop that they bump the insecticide seed treatment to a 500 rate or higher, and consider applying a pyrethroid at planting, if cutworms are present in the cover crop.”

He recommends growers burn down the cover crop three weeks before planting corn. “However, many don’t want to do this because of the weed control benefit, so they plant into green and then burn it down. That keeps a green bridge going so the insects spread from the dying cover crop into the emerging corn.”  

Tennessee Cover Crops

Pioneer

Larvae of southwestern corn borer: winter (diapause) phase (top) and summer phase (bottom)

More Tennessee growers are planting cover crops, says Scott Stewart, Extension entomologist at Jackson, and this requires even more consideration of insect management, particularly when the cover crops aren’t burned down until very near planting or after planting.

“When growers plant cover crops, particularly legumes such as vetch or winter peas, I recommend they use a higher insecticide seed treatment rate. They also can supplement the seed treatment with an in-furrow insecticide spray, such as bifenthrin.

“We use seed treatments on every corn acre, and we mainly plant Bt corn. Those two components generally control our spectrum of corn insects. Conventional corn is a totally different situation. We had an infestation of southwestern corn borer in a lot of our non-Bt acres in 2016. Another mild winter could really exacerbate the southwestern corn borer problem in conventional corn in 2017.”

Mississippi: Soil Insects

The soil insect complex is Mississippi’s No. 1 corn insect issue that growers deal with consistently, and an insecticide seed treatment is used on almost all those acres, says Angus Catchot, Mississippi Extension entomologist at Mississippi State University.

In the absence of a seed treatment, the soil insect complex would quickly escalate to the No. 1 corn insect pest status. “Insecticide seed treatments are very important to us. They control pests such as chinch bugs, wireworms, seed corn maggots, southern corn rootworms, white grubs, rootworms, sugarcane beetles — the whole complex — to various degrees.”

Mississippi corn growers sometimes deal with stink bugs in whorl stage corn. “We typically treat about 10 percent of our acreage for stink bugs in whorl stage corn,” Catchot says. “Dual gene Bt corn hybrids do a really good job of keeping caterpillar pests out of the whorl stage, but we do see earworms often infesting the ears, depending on the technology. Typically, ear infestations of corn earworm cause little, if any, yield loss, so it’s of little consequence.”

On non-Bt or refuge corn acres, he says, growers often contend with the corn borer complex — southwestern corn borers mainly, but some European corn borers. These can be adequately controlled with foliar sprays, but timing is critical. Fortunately growers can use pheromone traps to monitor populations and trigger insecticide applications. These thresholds have recently been modified based on several years of research, Catchot notes, and have been adopted and utilized extensively by consultants and farmers.

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