May 15, 2009
Late planting, weeds, the practice of no-till and the fact the many Indiana fields are in a corn-following-soybean rotation all combine to favor an increase in black cutworm activity, says Christian Krupke, a Purdue University specialist.
Wet conditions have kept growers and producers out of fields and from getting much of their preplanting fieldwork done, says Krupke, a Purdue Extension field crop entomologist. This has permitted the growth of weeds in and around fields, which ultimately favors cutworm growth by providing food, he explains.
“Because weeds are more abundant and larger now than in typical years, the black cutworm larval population will have more of a head start,” Krupke says. “This year we are likely to see larger and perhaps more numerous cutworms.”
Farmers should be vigilant and scout for black cutworms, Krupke recommends.
“Make sure you know which fields may be at risk,” he says.
Fields at risk are those that have lots of winter annual weeds, are planted late, practice no-till and are in a corn-soybean rotation. This year the first two conditions will be very common throughout the state, Krupke says.
“If you have one or more of those conditions, you should scout for black cutworms, even if you’ve never had damage before,” says Krupke. “This is a year to be on the lookout.”
Growers should scout twice weekly after the corn plant has emerged until the plant has five leaves, he recommends. He also says farmers should not rely on seed treatment of Poncho 250 to control cutworm damage this year.
“There is not enough Poncho 250 on the seed to kill cutworms immediately, especially since the cutworms are going to be larger in size than in most years,” he says.
Cutworms are one of the easiest insects to scout for because you can walk up and down the rows as the corn begins to emerge and look for leaf feeding and plants that have partially fallen over or are down on the ground, Krupke says. It will look like someone cut the plants with a pair of scissors, he explains.
“This will happen early in plant development because the cutworm is an early season pest that will feed on the plant, pupate and then leave, usually before the end of spring,” Krupke says.
Their activity takes place mostly at night, so growers should not expect to see the actual worm while scouting. They usually bury themselves under dirt clods during the day and stay out of the sun, Krupke says.
If black cutworm damaged is observed, it’s important to sample the field and assess if there is a threat posed by larvae, Krupke explains. To sample for cutworm, a grower should randomly select 20 consecutive plants in five different areas of the field and record the number of plants damaged by black cutworms, he says. While scouting for damaged plants, take note of the growth stage the corn is in – count and record the number of fully unrolled leaves on the last two plants in each of the five sets.
To determine the number of infested plants, add together the number of cut or damaged plants from each set of 20 plants and divide it by 100. To determine the average number of fully unrolled leaves per plant, add together the number recorded for each of the 10 plants and divide the sum by 10.
Control measures may be needed if 3-5% of the plants show leaf feeding or two or more cutworms can be found for every 100 plants.
The black cutworm is the only adult cutworm species monitored in Indiana, but other species a grower might come across include the clay-backed cutworm and the dingy cutworm. While scouting for black cutworm, producers should also be on the lookout for flea beetles, a vector of Stewart’s wilt, Krupke says. Flea beetles are usually found near a field’s perimeter.
More black cutworm information is available at Purdue University Black Cutworm. A list of insecticides and rates for black cutworm control is downloadable at http://extension.entm.purdue.edu/publications/E-219.pdf. For additional questions and information contact Krupke at 765-494-4912 or [email protected].
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