Abnormally hot spring weather changes crop pest dynamics

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Insects are developing early in farm fields this spring because of unseasonably warm weather, making it even more important for farmers to inspect their crops, a Purdue Extension entomologist says

One such insect is the Western bean cutworm, which typically feeds on Midwestern corn but also occasionally can be found in soybean fields. Western bean cutworm moths normally are not seen until late June and early July, but they have been showing up in pheromone traps throughout Indiana since the beginning of the month.

There is a correlation between the record-breaking temperatures and the early insect maturation, Christian Krupke said.

“Plant development was early, and insect development was also early. These things are both primarily temperature driven,” he said.

Farmers around the region need to set and keep an eye on pheromone traps to determine when they should start scouting their fields. When the number of trapped moths peaks (often double- and triple-digit numbers of moths per week), fields should be inspected for eggs, Krupke said.

He advised checking pre-tassel corn and inspecting the upper side of the newest upright leaf, where eggs typically are laid. At least 100 plants should be inspected, and if 5 percent or more of the inspected plants have eggs on them, farmers should treat their fields. Western bean cutworm eggs are creamy-white in color at first and darken to a purplish color before hatch. They are usually laid in groups of 20-50 eggs per cluster.

“If you don’t treat early, you won’t get them. Once they enter the whorl and later the developing ear, they cannot be contacted with insecticides,” Krupke said. Growers may be seeing eggs in spotty locations already, and they will peak at the end of June.

Researchers estimate that if there is one cutworm per ear of corn in a field, the farmer will lose four to six bushels per acre. But the insect is what Krupke referred to as a “minor pest” because, in Indiana, growers have never seen populations that high over an entire field.

There are many insecticides labeled for this pest, and they provide excellent control if applied on time, Krupke said. But if fields remain untreated, Western bean cutworms could begin feeding on the ear.

Ear feeding creates an “entry point” for the fungus Gibberella zeae, which causes Gibberella ear rot, explained Kiersten Wise, Purdue Extension plant pathologist.

This particular fungus can produce a byproduct that results in increased levels of mycotoxins in the grain, leading to livestock feed refusal and reproductive problems. She explained that the weather conditions when plants tassel will determine whether infection will occur by this fungus.

“It really depends on the environment,” Wise said, adding that cool, wet weather offers prime conditions for this disease to prosper.

More information about Western bean cutworm is available in the June 8 edition of Purdue Extension’s “Pest and Crop Newsletter” at http://extension.entm.purdue.edu/pestcrop/2012/issue11/index.html#western



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