Southwestern corn borer now in Ohio


SALEM, Ohio – Corn producers, beware: Larvae of the pesky southwestern corn borer have been found in Ohio.

The borer can cause severe crop damage, lodging and yield losses.

Migrating. Southwestern corn borers are a common problem for growers in the southwestern United States, with a presence stretching from Arizona to Georgia and north to Illinois.

In recent years the pest migrated into Kentucky and southern Indiana.

The wet winter of 1977-78 wiped out the pest in the northern part of the range, according to Garst Seed Company agronomist Eric Anderson, but the pest made a comeback in the early and mid-1990s.

Coming here. During field scouting March 9, Garst agronomists found larvae along the Ohio River in Brown and Adams counties in southwestern Ohio.

“We anticipated they would be there, it was just a matter of time,” Anderson said, noting the borer has caused significant problems in Kentucky and southern Indiana since 2000.

The borer was found in less than 1 percent of scouted stalks, which means it’s not a big deal at this point, Anderson said.

“We know if we see a 15 percent incidence rate, that’s fairly closely tied to economic losses,” he said.

“In these fields, with less than 1 percent, if you didn’t know what you were looking for you wouldn’t even notice it.”

Anderson also said he has scouted or plans to scout fields in Hamilton, Butler, Preble and Clermont counties.

He and other agronomists are using pheromone-baited bucket traps to attract and kill males of the species. The traps also help track infestation levels.

Triple threat. While similar in biology to the European corn borer, the southwestern corn borer is more aggressive and difficult to control, Anderson said.

This borer has two or three generations per year and can potentially cause more damage than the European variety.

“A lot of growers had significant economic loss in 2003 from the European corn borer. This can make those losses seem small,” Anderson said, noting 30 percent to 50 percent losses are realistic.

Waiting to strike. The borers overwinter in the base of the stalk below the soil.

The larvae will turn to moths in late April and early May. Those moths will survive five days and lay up to 400 eggs, Anderson said.

The second and third generations cause the greatest damage as they feed at the mid to lower nodes of the plant when corn reaches the tassel stage in mid to late July.

Larvae “girdle” the plant by chewing an internal groove around the stalk near the base in late August and early September.

The girdling causes stalks to lodge, making it nearly impossible to harvest.

Immediate concerns. Anderson said there are no immediate concerns for Ohio corn growers because only a small population has been found.

Anderson said studies have shown eastward migration at a rate of 13-30 miles a year, and northward migration at about 9 miles per year.

Watch for signs. Growers with suspicions about the borer can take action now.

Anderson recommends digging and splitting a root ball from a plant that was girdled last crop year. An overwintering larvae will still be in the root of the plant, he said.

Through the growing season, the larvae are distinguishable from European corn borers because they have spots, he said.

Plant, harvest early. Agronomists recommend planting and harvesting early. Fields planted after May 1 are more at risk of damage by the second and third generations of the borer.

Getting the crop in early can also up the exposure to European corn borer, Anderson said.

Early harvest at 25 percent moisture gets the crop out of the field before severe lodging occurs.

Insecticide sprays. First generation corn borers should be treated similar to how farmers handle European corn borer – treat 20 percent to 35 percent infested plants with live borers present, Garst recommends.

Second generation borers can be treated with insecticide spray at 20 percent to 35 percent infested stalks with eggs and live borers present.

Second generation treatments should be made in conjunction with a pheromone trapping program to maximize control by hitting peak moth flight, the company says.

Bt corn. In areas with established southwestern corn borer populations, YieldGard Corn Borer Bt corn hybrid offers an effective management tool.

(Reporter Andrea Myers welcomes reader feedback by phone at 1-800-837-3419, ext. 22, or by e-mail at


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