Get a Better Handle on Black Cutworm Threat

Get a Better Handle on Black Cutworm Threat

Will black cutworms still threaten late-planted corn?

The answer to the lead question: 'will black cutworms still threaten late-planted corn?' is a crystal-clear 'yes, maybe, well it depends.' If you're considering opting for an insecticide in a burndown treatment for black cutworms in fields that aren't planted yet, you might want to read this explanation and digest it before you make a decision.

It all revolves around the life cycle of the black cutworm, and the difference in behavior of corn depending upon when it's planted, says John Obermeyer, Extension entomologist at Purdue University.

Black cutworms don't overwinter in Indiana. Instead, they overwinter in Gulf States and ride up on spring storms. With so much storm activity this spring, moth counts in traps operated by entomologists are high and continue to be high. If corn is up now, it's definitely at risk. The real question is what about corn still in the sack? If It's planted by May 25 or June 1, will it still be at risk?

As it turns out, black cutworm moths love vegetation, preferably green vegetation, to lay eggs. Larvae from the first eggs laid by the first moths that arrived in Indiana have hatched and are feeding on plant material in fields. Those larvae may have already completed their life cycle and become moths and flown away before some corn is ever out of the ground. For those moths, their target becomes green areas to lay their eggs, such a golf courses.

"The fact is that black cutworms don't like cornfields for egg laying," Obermeyer says. "If eggs are laid in a field that goes to corn, hatch out and there's nothing else to eat, they'll eat corn. But that's not their preference."

The rub comes in the fact that black cutworm moth arrival is a continuous event, not a one-time event. Moth counts found in traps continues to be strong yet this week, the entomologist notes. That tells him that even if corn doesn't emerge until late May or early June, black cutworms could still be a threat.

However, corn planted in late May or early June will likely pop out of the ground in three to four days rather than two to three weeks if it was planted in April. That means each corn borer is likely to be able to cut fewer plants before corn is past the stage it affects, he notes. This would help minimize damage.

Some may go ahead and opt for including an insecticide in their burndown mix this time just in case. Obviously, if you get hit with a bad black cutworm infestation and lose lots of plants in patches within a field in early June, there won't be time to replant.

From an integrated pest management standpoint, however, including the insecticide as insurance is not a wise choice. It may turn out that it's not needed anyway. If so, you just dumped insecticide into the environment that wasn't needed. It would also be an economic cost as well.

Weigh all the facts. Then make your decision.

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