By Linda Geist
University of Missouri Integrated Pest Management has issued its first pest alerts of the growing season.
MU Extension state field crops and forage entomologist Ivair Valmorbida says corn and wheat growers should be on the lookout for early season pests, including black cutworm and true armyworm.
Significant numbers of black cutworm moths have appeared in some regions, with predicted cut dates for the first week of May in Missouri. The cut date is the estimated date when black cutworm damage may be seen in the field. It is based on actual and estimated temperatures.
MU Extension specialists across the state monitor traps and count the number of pests. If numbers exceed certain levels, the IPM Pest Monitoring Network issues a text alert to subscribers.
Black cutworm
Black cutworm is a migratory pest in Missouri, likely from moths from the Gulf Coast or Mexico.
In corn, black cutworm damages seedlings by cutting plants at or below the soil surface. When soils are dry, cutworm drags the plant to its burrows to feed.
To determine management options, scout for larvae when corn emerges, says Valmorbida. Examine 25 corn plants at each of 10 widely distributed areas in a field. Repeat every 7-10 days until corn reaches the V4-V5 growth stage.
Because yield reduction is related to the site of injury on the seedling plants, there are different thresholds for damage to corn above and below the ground. Rescue insecticide treatments are recommended when 2% to 4% of the corn seedlings are cut belowground and 6% to 8% of the seedlings are fed upon or cut aboveground.
True armyworm
Scouting for true armyworm saves money and reduces insecticide use, Valmorbida says. It feeds on several crops, including wheat, corn and forage grasses. Scouting procedures and thresholds for insecticide application vary among these crops.
Larvae begin feeding at leaf edges and continue in toward the midrib, which is not eaten. The larvae usually do not feed during the day, so scout early in the morning or just before dusk.
In wheat and forage grasses, larvae feed primarily on leaves.True armyworm larvae will sometimes chew completely through wheat peduncles (head clipping), and the entire head will fall to the ground.
The threshold for insecticide treatment for wheat and forage grasses is an average of four larvae per square foot. Ignore larvae larger than 1 inch because they will soon stop feeding and pupate. Because head clipping reduces wheat yield so much, insecticide application should be made if 2% of heads are clipped and larvae are present.
Growers can receive free IPM Pest Monitoring Network alerts when insect captures exceed certain thresholds. Go to https://ipm.missouri.edu/pestMonitoring to sign up.
More information from MU Extension
You can also contact your local MU Extension agronomist for information.
Source : missouri.edu