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WVU Extension Service Issues Warning About Fall Armyworms

Photo Provided by WVU Extension Service Fall armyworms are reportedly causing significant damage to area lawns and fields.

WHEELING – In their larvae stage, fall armyworms can feed as a group and can devour an entire lawn or hay field in a matter of days, according to officials with the West Virginia University Extension Service.

In fact, the extension service has received enough calls about the armyworm recently that they posted an “AgAlert” on the topic, cautioning area residents to be proactive against what can be a menacing pest for area farmers or landscapers.

Extension service officials suggest area residents monitor their lawns and fields through September, as the armyworm can leave behind what appears to be large areas of “burned out” or “browned out” turf or field which can resemble the damage caused by a drought.

According to the WVU Extension Service, in late June, armyworms begin arriving in West Virginia from the south.

Shortly after, eggs are laid in masses on the undersides of plant leaves, tree trunks, undersides of tree limbs and other structures near suitable host plants, such as fences, bleachers and light posts.

The name ‘armyworm’ originally came about because where there are large infestations, it can resemble an army as they move across large fields, according to Karen Cox, West Virginia University Extension Agent for Ohio County. She said outbreaks, or large numbers of the armyworm, usually occur every few years in the region.

“This is typically more of a problem in the southern states. It’s usually not a big problem here,” Cox explained. “We believe that because of the hurricanes and storms that have pushed air up from the south, that these (armyworm) moths hitched a ride basically and came up here earlier than normal and therefore they were able to have more generations than normal.

“And each time they lay eggs and hatch you have that many more caterpillars to deal with,” she added.

The armyworm larvae feed as a group and can devour an entire lawn or hay field in a matter of a few days, according to extension office officials. Damage is caused by the larvae (caterpillars) when chewing plant tissue — causing the grass to appear thinned out of brown. This appearance is the result of grass plants rapidly dehydrating after armyworm larvae damage the grass. For this reason, the damage they cause often resembles drought damage.

“With the outbreak that we’re having, it’s been significantly impacting our pastures and hayfields and reducing the grasses that we have available for our livestock to eat,” Cox explained. “But it’s also affecting people’s yards and golf courses, which can lead to erosion problems if there’s no cover. So we’re encouraging people if they have a problem and have questions to reach out to us. For some of our farmers it has been menacing.”

According to the U.S. Department of Agriculture, the armyworm is a destructive pest that can feed on 80 different crop species, including corn. The larval stage of armyworms can also cause rapid, significant loss of leaf tissue in turfgrass. They feed primarily on bermudagrass, ryegrass, fescue, and bluegrass, but can also be pests of agricultural crops.

Farmers and turfgrass managers should scout their fields every three to four days to monitor for caterpillars through the end of September. Treatment is recommended when more than three worms of quarter inch in length or greater are found in a one square-foot area. Control of the armyworm will depend on the coverage with a recommended pesticide. It is also recommended to mow the lawn or field prior to treatment.

According to the WVU extension Service, several insecticides with different active ingredients kill armyworms. Spinosad, chlorantraniliprole, azadirachtin, pyrethrins, neem oil, methoxyfenozide are reduced risk insecticides that are labeled against this pest. Products with the active ingredient Bacillus thuringiensis can be used to control the younger larval instars.

The feed of armyworms is eventually reduced by cold temperatures and the insects will eventually die with the first fall frost, according to Cox. For more information contact your local WVU Extension Service Office. The WVU Ohio County Extension Service phone number is 304-234-3673.


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