Corn Chewing Begins

17 May 2017

By Emily Unglesbee
DTN Staff Reporter

ROCKVILLE, Md. (DTN) -- If your corn survived heavy rains, flooding and cold soils, you're lucky -- but you're not safe.

The recent welcome wave of heat and sun in the Midwest is speeding along insect development just as well as crop growth.

Armyworms and black cutworms should be on the top of your scouting list in the weeks to come, said entomologists from across the Corn Belt. Scientists tracked extremely large moth flights of both pests back in March and April. That means the eggs they laid will soon hatch hungry larvae.

Other insect pests of corn to watch for include slugs and the white grubs that will develop into May and June bugs.

CUTWORMS AND ARMYWORMS

The farther south in the Corn Belt you live, the sooner you will see black cutworms and armyworms active in your fields.

"We've been tracking heat units for the cutworm, and to date, many southern counties in Indiana are to the point where they could see damage in corn," Purdue University IPM specialist John Obermeyer told DTN.

Armyworm larvae should be on a similar timeline, and will favor fields that had heavy grassy vegetation (such as wheat, rye and grassy weeds) early in the season when the moths were laying their eggs, Obermeyer said. Likewise, black cutworm moths prefer fields with winter annual weeds and heavy crop residue, University of Nebraska Extension entomologist Bob Wright said in a university newsletter.

Scout those fields, and don't assume your Bt hybrids or treated seed are bulletproof.

"High populations of insects can overwhelm the protection method, regardless of whether it was an insecticide applied at planting (liquid, granular, or seed treatment) or a Bt corn hybrid," Wright wrote.

After heavy rains and wet soils, high populations of cutworms and armyworms aren't guaranteed. Entomologists do know fields entered May with very high egg counts.

"It doesn't take a whole lot of survival to put a field at risk," Obermeyer said. "In some cases, just 1% survival could do it."

For help scouting and treating black cutworm, see this guide from the University of Minnesota: http://bit.ly/…. For help scouting and treating armyworm, see this guide from the University of Kentucky: http://bit.ly/….

SLUGS AND WHITE GRUBS

Farmers on the eastern margins of the Corn Belt are no strangers to slug infestations.

This year, growers in central states might also get a taste of this pest, which thrives in wet conditions, warned Obermeyer.

"The later the corn goes into the ground, the more vulnerable it is to slug infestations," he said. "When juveniles are hatching and growing at same time as the corn crop, which is just emerging in many fields, that's when we get problems."

Keep in mind that because they are not insects, slugs are not controlled by seed treatments or Bt proteins, Obermeyer said. For more help scouting and treating slugs, see this guide from Penn State University: http://bit.ly/….

"True" white grubs can also pose a risk to seeds and seedlings, said Iowa State Extension entomologist Erin Hodgson. These grubs are on a three-year cycle and will eventually become May or June beetles.

Seed treatments can protect against white grubs, but if you suspect damage or stand loss from them, see this Iowa State University guide: http://bit.ly/….

Don't confuse the bad guys with the clean-up crews when you're scouting, Obermeyer added in a Purdue newsletter.

Insects such as millipedes, juvenile earthworms and potworms generally do not prey on healthy, live plant tissue. Earthworms are actually physically incapable of doing so, Obermeyer pointed out.

"Their mouthparts are incapable of causing damage to live tissue -- they don't have "teeth" and instead are specialized to suck up partially-liquefied material," he explained.

So if you see these worms or millipedes swarming a seed or seedling, it has likely already succumbed to disease and is in the "early stages of decay," Obermeyer said. "In short, they're 'good bugs' turning decaying plant material into soil."

See his article here: http://bit.ly/….

Emily Unglesbee can be reached at Emily.unglesbee@dtn.com.

Follow Emily Unglesbee on Twitter @Emily_Unglesbee.

(GH/PS/ES)