Kelly Hamby, Extension Entomology Specialist, University of Maryland | kahamby@umd.edu
and David Owens, Extension Entomology Specialist, University of Delaware | owensd@udel.edu
A fall armyworm outbreak is occurring throughout Virginia, Kentucky, and Ohio. This week, we received a report of armyworm damage to sod from Maryland’s Eastern Shore as well as residential lawns in Lewes, Delaware. This appears to be one of the most significant armyworm flights in many years. Scout turf, sod, pasture grasses, any late sweet corn that has not yet headed, and when the time comes, small grain and cover crops. Females lay egg masses containing between 50 and 200 eggs, meaning damage can be localized and intense and that it does not take many moths to infest a field. It is important to catch an infestation as early as possible. Larvae consume 80% of their total intake during the last three days of larval development. Often, it is during this period or just after larvae have finished that damage is noticed, occurring seemingly overnight as if an army had stripped the field. It takes about 14-19 days for larvae to mature.
Recommendations from southern states that deal with armyworm more regularly are to sample 1 sq. ft, if there are more than 3 armyworms ½ inch long, a treatment is warranted, but if worms are 1 ½” long, they are close to pupating. We have many options for armyworm control in pastures including Pyrethroids, IGRs (ex Intrepid), Diamides (Vantacor and premixes like Besiege), spinosyns (ex Blackhawk) and Lannate. Growth regulators are slow acting, thus are only going to be effective on small worms. Before treating armyworm, remember to read labels carefully; the label is the law.
