Fall Armyworms Make Summer Appearance

 Fall armyworms plague many Mississippi pastures, lawns and sports fields, but vigilance 
 and prompt treatment can limit their damage.
 Photo by MSU Extension Service/Blake Layton


   Although 2016 brought unusually heavy infestations of and damage from fall armyworms, vigilance and prompt treatment can limit damage this year.
Blake Layton, entomologist with the Mississippi State University Extension Service, said fall armyworms were a problem in commercial hayfields, home lawns, sports fields, golf courses and commercial landscapes last year.
   “Fall armyworms caused extensive damage, and their presence prompted several insecticide applications to control them,” Layton said. “Mississippi gets fall armyworms every year, but they don’t always appear in numbers as high as seen in 2016.”
   Layton said the fact that fall armyworms do not overwinter in Mississippi makes it hard to predict their numbers each year.
   “The armyworm moths have to migrate back into the state each year from the Caribbean, Mexico and other areas of South America,” he said. “Severity and distribution of fall armyworms depends on when moths arrive, how many moths arrive, where in the state they arrive, and weather conditions they experience once they get here.
   “In other words, it depends on how the wind blows,” Layton said.
   Fall armyworms are the most damaging insect pests of Mississippi hayfields and pastures. These caterpillars can destroy a cutting of bermudagrass in just a few days. A good hayfield can produce a few hundred dollars’ worth of hay per acre, making this an expensive pest to have.
   Fall armyworms also are troublesome pests of home lawns and sports fields. Newly established bermudagrass lawns and sports fields are the most susceptible.
   “During the summer, it takes about 14 days for fall armyworm caterpillars to grow to maturity and be ready to pupate,” Layton said. “As with many other caterpillars, they do 80 to 90 percent of their eating in the last two or three days of their life. A bermudagrass hay field that is lush and pretty when the farmer drives by to see if the field is ready to cut can be severely defoliated two days later when he returns with the mower.”
Vigilance is the best defense against these pests.
   “Learn to scout for fall armyworms and learn to recognize early signs of infestation,” Layton said. “Check your hay fields or bermudagrass lawns and turf regularly, and be prepared to treat promptly once you detect an infestation.”
   Through the summer months, hay producers should check maturing fields two or three times a week to avoid losing yield and income to fall armyworms. There are many effective insecticides for controlling fall armyworms, but insecticides only help protect yield when applied before serious damage occurs.
   Keith Whitehead, MSU Extension agent in Franklin County, said fall armyworms cause many problems in pastures in the area.
   “The caterpillars are usually identified and treated rather quickly in home lawns and sports fields with only aesthetic injury sustained in most cases,” Whitehead said. “In pastures, fall armyworms often go unnoticed until forage production has been severely affected.”
   Whitehead said once fall armyworms have been identified in the area, most producers are good at scouting their fields, but they may not be prepared to take action.
   “When heavy infestations arrive in the area, local farm-supply stores often quickly sell out of the insecticide products required for treatment,” Whitehead said. “If forage producers do not have a product on hand, the delay in treatment will result in greater loss.”
   Fall armyworms reach south Mississippi after overwintering in the tropics, and infestations in that part of the state indicate how the rest of the state will be impacted.
   “When the southern third of the state experiences heavy infestations of fall armyworms in June, this usually indicates that, if weather conditions permit, they will impact most of the state at some time during the year,” Whitehead said.
   Search the MSU Extension Service website at for information on fall armyworm control in hayfields, pastures, home lawns and commercial turf. These publications include information on how to detect the pest, thresholds for when treatment should begin and what chemicals can be used in specific situations. ∆
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