Cutworm infestation likely in area

Black cutworm infestation likely in Missouri
COLUMBIA, Mo. - Farmers with late-planted corn should prepare for black cutworm damage. Wet soils and heavier weed cover in fields will make the insect a potential problem this year, said a University of Missouri Extension entomologist.
"This is a perfect year for black cutworm," said Wayne Bailey. "The whole northern part of Missouri is at risk, but we've had the heaviest moth captures in the northeast. This means there is a high risk of black cutworm in that area," Bailey said.
Winter annual weeds like henbit and chickweed add to the risk. "Black cutworm moths tend to lay their eggs in fields with vegetation, because their larvae can feed on that prior to feeding on corn," he said. "But these plants will be older and tougher when corn emerges, and so they will go for the corn."
Late-planted corn is a perfect target for the insect. Wet fields delay planting, but attract cutworm moths to lay eggs. When corn plants emerge, there will be more and bigger cutworm larvae to attack seedlings. When corn is planted on time, emerging plants have a head start on growth before larvae reach the cutting stage.
"They can cut above or below ground. If they cut above ground, the corn may come back in one to two weeks, depending on field conditions," he said. "If they cut underground, that's closer to the growing point. The plant could die, but if it lives, the yield potential is reduced."
Black cutworms are considered the most damaging corn cutworm species. Moths overwinter in southern states and migrate north on winds in storm fronts from mid-March to June.
While cutworms rarely damage an entire corn crop, farmers can lose up to 50 percent of their plants in heavy infestations if cutworms go undetected, Bailey said. Farmers will know if a stalk was cut by a worm if the cut line is horizontal. Diagonal cut lines are likely caused by voles, he said. Wilting plants are one sign of worm cutting.
Bailey said farmers should start scouting fields for signs of foliar damage or cutting five to seven days before the predicted first cutting date for their area, and continue scouting until corn reaches the five-leaf stage. Cutting dates are based on when the first intensive moth captures took place.
For northern Missouri, the predicted first cutting is May 17. Other dates are May 11 for western Missouri near Nevada and May 13 for eastern Missouri near Union and St. Louis.
"In the northeast, I'd definitely be out there scouting," Bailey said. "The larvae are small and nocturnal, so they may be hard to see. But you may be able to see defoliation on plants. If you don't see feeding, it doesn't mean you shouldn't look again at the predicted cutting date."
Farmers have three options to handle cutworms. First, plant seed corn treated with insecticide. "But those worms will be large, and if their numbers are heavy, it will take a high dose to knock their numbers down," he said. "So seed treatments will be less effective this year."
A second option is to use an early-season spray to knock down heavy populations. "We don't usually recommend this method, because we like to know the pest is present first. But if populations will be heavy, it is viable," he said.
Bailey said the preferred strategy is to scout fields and apply insecticide where needed to rescue plants from the worms.
"If the cutworms are below ground and they're cutting 2 to 4 percent of your plants, I would put a foliar rescue on top," he said. "Once you've sprayed, check back in about three days to make sure there are no more cuttings."
Once corn plants reach the six-leaf stage, they are less vulnerable as their stems are usually too thick for worms to cut.
"We will worry about corn until it is about 6 to 7 inches tall," Bailey said. "Usually the worms are down feeding near the ground. On wet soils, they tend to surface feed, whereas on dry soils they tend to feed underground - so we have that going for us."
For more information on black cutworms or the MU Extension black cutworm monitoring program, visit http://agebb.missouri.edu/weather/reports/bcwforecast.htm.