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Armyworms are on the march in East Texas.
"This time they're everywhere, in home lawns, pastures and hay meadows. It looks like this infestation is much larger than those in July and early August," said Dennis Smith, agriculture and natural resource agent with Texas Cooperative Extension in Gregg County. Smith and other Extension agents in East Texas have been getting more calls than usual this year. The outbreak has to do with the weather, said Allen Knutson, Extension entomologist.
Outbreaks typically happen in the fall, and for reasons unknown are worse when rains are frequent and temperatures are cooler, said Knutson, who is based in Dallas.
Fall armyworm moths migrate in the millions, literally, northward from South Texas in the spring and summer. As part of its natural life cycle, each moth will deposit a clump composed of 50 to100 eggs on individual blades of grass.
The moths persistently continue to migrate and lay eggs throughout the fall. When their egg-laying coincides with a rainfall, fall armyworms hatch in droves and immediately start maneuvers.
The eggs yield tiny armyworm larvae which feed on leaves for two to three weeks.
"Young larvae don't eat much, and infestation can easily go undetected as little damage to the pasture or hayfield is visible from a distance," Knutson said. "However, once larvae reach about 3/4-inch long, their appetites greatly increase. During the last week of their development, armyworm larvae eat 80 percent of their total food intake. For this reason, damage can occur very quickly and hay fields or pastures can seem to disappear almost overnight."
The best counterattack against an armyworm invasion is treat with pesticides when larvae are small and have yet to do extensive damage, Knutson said. Also, sometimes using chemical controls may be a Pyrrhic victory in economic terms; the producer may control the infestation, but spend more money than would be made from the use of the pasture or harvest of hay.
"As a general guideline, if three to four or more armyworms are present per square foot, economic loss is likely and an insecticide treatment should be considered. If plants are small with few leaves, two to three larvae per square foot may be a damaging level," Knutson said.
Malathion and carbaryl are the standard insecticides for armyworm control in pastures and hayfields. Malathion has no restriction on delays between use and grazing or harvesting hay, whereas carbaryl (Sevin) has a 14-day waiting period after application before grazing or haying, Knutson said.
Tracer is also approved for armyworm control in pastures and hay fields under a section 18 specific exemption. This label is currently scheduled to expire on Sept. 23. There is no restriction on grazing and the waiting period for harvest is three days after application, he said.
"Refer to the insecticide label for information on the required waiting period after application and before grazing or harvesting treated crops," Knutson emphasized.
For homeowners, cost of treatment does not come into play. They simply want to preserve their lawns or rid them of an unsightly pest. It's more a "squish" threshold than an "economic" threshold, Knutson said.
"For armyworm control in lawns, there is a long list of labeled products," he said. "Insecticides containing cyfluthrin, permethrin, lambda-cyhalothrin, orthene, malathion and carbaryl which are labeled for use on lawns and turf provide control of armyworms."
Most products approved for home lawns are less concentrated than those used for production agriculture. Usually, people can venture out on the lawn as soon as the application dries. Otherwise, there's not that much difference between an armyworm infestation of a pasture and a home lawn.
"Armyworms will eat almost any plant once they start marching and looking for food, so vegetable gardens and other gardens would be at risk from armyworms moving from adjacent grassy areas," Knutson said.
Most of the products labeled for use on home lawns cannot be used on vegetable gardens Knutson said.
"Products containing carbaryl and malathion are labeled for application to home gardens and vegetables," he said. "A relatively new product for some vegetables (tomatoes, radishes, carrots, etc) is cyfluthrin, sold as BayerAdvanced Garden Multi-Insect Killer."
For more information, contact the Extension office in your county, which is usually listed in the telephone directory under the "county offices" section. More information on fall armyworms and other agricultural pests can also be found at the Texas A&M University Department of Entomology Web site at http://insects.tamu.edu/imagegallery/ .
