Crop Scene Investigation - 33 Solved: Which pest invaded Jeffrey's corn field?

Friday, May 6, 2011

About one-third of the larvae in Jeffrey's field were not western bean cutworm. These pests had yellow and greenish bodies, a tan-coloured head and distinctive black dots along their body.

by BERNARD TOBIN

Jeffrey had assumed that all the pests chewing on his corn were western bean cutworm (WBC). But on closer examination, about one-third of the larvae were actually corn earworm (CE). Feeding patterns of the two pests are similar.

"In the early stages, it's difficult to tell them apart, but once they become bigger, it's easier to distinguish between the two," says DeKalb agronomist Bob Thirlwall. "Western bean cutworm becomes more of a creamy colour and can grow bigger than a corn earworm, which is darker in colour and has distinctive black dots along its body."

Thirlwall says Jeffrey's case is a prime example of why growers should never assume that they're dealing with just WBC. "This year we saw some fields that had western bean cutworm, corn earworm and fall armyworm," he says noting that European corn borer is another culprit that could have an impact on yield.

Thirlwall also notes that CE is a migratory pest that may not appear in the field the following year, but there is growing evidence that WBC will overwinter in fields in Ontario.
"Once you identify the pests, a discussion with your seed supplier will help you choose the right trait option to manage the insect pressure," says Thirlwall.

"But it's important to remember that you need a hybrid that has the right genetics and the right agronomic fit for that particular field," adds Thirlwall. "Traits can solve one piece of the puzzle, but if you have a clay hybrid on a sand farm you could have other issues."

Congratulations to Gord Jones, Centralia for his correct answer. BF