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Invasion of the fall Armyworm

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Weather conditions have been perfect the last week or so to produce the fall armyworm. These outbreaks occur following a rain and cooler temperatures. The fall armyworm gets its name from the occurrences in the fall and the army like march across your lawn or pasture consuming the grass along the way. They are a common pest of Bermudagrass, sorghum, corn, wheat and rye grass among many other crops.

The fall armyworm can be identified by its color of green, brown or black and the distinct white line between the eyes that form a “Y” pattern. These are not actually worms but are caterpillars that will turn into moths. The caterpillars grow to about 1 to 1.5 inches long. The life cycle of the fall armyworm takes 2-3 weeks to complete and there can be 4 to 5 generations each year. The life cycle begins when the female deposits eggs into the soil which can number up to 2000 eggs. These eggs hatch with caterpillars that are about 1/8 inches long after favorable weather conditions are met. The caterpillars then feed on the grasses until they reach 1 to 1.5 inches in size and then burrow into the soil. They emerge about 10 days later as moths and the process starts over again.

The fall armyworm feeds during the night and will avoid hotter daytime temperatures. You should scout your fields and lawns either in the early morning or late afternoon. The threshold suggested to treat you lawn or pastures is 3 or more armyworms per square foot. Armyworms consume 80-85% of their diet in the last 2 to 3 days of the larvae stage and can do a lot of damage in a few days. If you meet the treatment threshold spray that day, don’t wait too long and treat the same day.

The key to managing fall armyworms is frequent inspections before they have cause economic damage. If spraying, spray in the early morning or late afternoon when larvae are most active and can come in contact with the insecticide. If the pasture or hay field is near harvest, then an early harvest is an option rather than applying an insecticide.

Always read and follow label directions when applying insecticides. Following are a few active ingredients in insecticides that may be used to help in controlling the larvae:

▪ Lambda-cyhalorthrin, S-Cyano, Cyfluthrin, Diflubenzuron, Chlorantraniliprole, Carbaryl, Malathion, Methoxyfenozide.

For the homeowner when larvae are small a low impact insecticide like halofenozide and spinosad can be used. Bacillus thuringiensis (Bt) products will control larvae and not cause harm to beneficial insects. Conventional insecticides for the home lawn include bifenthrin, carbaryl, esfenvalerate and permethrin.

For questions or more information please call County Extension Agent Jay Kingston Texas A&M AgriLife Extension Service Parker County at 817-598-6168 or email to j-kingston@tamu.edu

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