Planting Time and Rootworms

April 30, 1999
I recently received an interesting question about the time of planting and concern about rootworm larvae causing damage to corn seedlings. Because of the wet soil conditions, planting has been delayed throughout much of Illinois; with predicted warmer and drier weather, corn producers will be planting aggressively within the next few days. Apparently some people are concerned that planting at this "late date" might expose the root systems of corn seedlings to serious injury by rootworm larvae.

Let's keep in mind that planting in early May is not considered "late planting" by most accounts. Although growers plant corn much earlier these days than they used to (some corn in Illinois was planted in late March), planting corn in early May is still okay. And despite the trend to plant corn early, the time of year when rootworm larvae hatch from eggs has not changed much. We still anticipate that rootworm larvae will begin hatching in late May or early June. When the soil is cool and wet, hatching may be delayed. In 1997, hatching didn't occur until mid- to late June; that was unusual.

If corn is planted early in May and rootworm larvae do not begin feeding until late May or early June, the root systems of most plants will be substantial enough to accommodate the rootworms. In fact, the first two instars do not cause nearly as much serious damage as the third instar, which won't be feeding until well into June. So don't be concerned about rootworm larvae devastating root systems of seedling corn, unless the corn is planted very late. Although rootworm larvae have caused damage to seedling corn plants in the past, the occurrence has been rare.--Kevin Steffey

Author: Kevin Steffey