Armyworm activity increases in crops
University of Missouri Extension agronomy specialists have been monitoring armyworm activity in corn, wheat and fescue fields in Missouri. One tool used statewide to monitor activity is the armyworm trap.
Though exceptionally high levels have not been seen, there is currently armyworm activity in southwest Missouri fields and it should be monitored.
"Young corn seedlings and plants can be at risk," said Tim Schnakenberg, agronomy specialist with MU Extension. "The economic threshold for spraying this pest is when 25 percent or more of the plants are being damaged."
If the outbreak elevates to a high level, armyworms can consume a large amount of foliage and stunt the crop. Schnakenberg says it is important to check seedlings and whorls for leaf feeding.
"Fescue seed and wheat producers should also be watching closely because large numbers of them may not only defoliate the plant, but they can clip heads as well," said Schnakenberg.
Treatment is justified in pastures and wheat fields when an average of four or more half-grown or larger larvae can be found per square foot and before more than two or three percent of the heads are cut.
Dusk or dawn is the best time to be scouting for armyworms because the young larvae are typically night feeders.
"During the heat of the day they will be under plant debris on the ground. As the larvae get bigger they will do an increased amount of day-time feeding," said Schnakenberg.
The larvae have a greenish-brown body, nearly hairless, with two orange stripes along each side. The head is brown with honeycomb markings and an inverted "V" marking on the top.
Schnakenberg says that once the moths move into an area, they lay their eggs and it may take two to three weeks for the young larvae to start doing damage. It only takes the larvae five to seven days for them to grow from one-half inch to 1.5 inches in length.
Producers can also monitor insect activity in Missouri through the Missouri Pest Monitoring Network at http://ipm.missouri.edu. On this website, producers can find insect activity such as armyworm, cutworm, Japanese beetle, corn borer and corn earworms reported in traps maintained by MU Extension agronomy specialists.
Producers can also sign up for a free email notification if an insect alert occurs around the state.
For more information, contact any of these MU Extension agronomy specialists in southwest Missouri: Tim Schnakenberg in Stone County, 417-357-6812; Jay Chism in Barton County, 417-682-3579; John Hobbs in McDonald County, 417-223-4775 or Brie Menjoulet in Hickory County, 417-745-6767.