From an article by Jennifer Grant, NYS IPM with contributions from Keith Waldron and Dave Shetlar from the June 11 ShortCUTT newsletter.
True armyworm (aka Common armyworm) larvae are being found across New York State. They do not overwinter in New York, but fly north from states to our south in the spring. Armyworm moth migrations are somewhat sporadic, cyclic from year to year, and difficult to predict. Our last notable infestations in New York occurred in 2001 and 2008. True armyworms are primarily a pest of plants in the grass family: forage / pasture /grasses & lawns, small grains and corn.
True armyworm larvae appear smooth, cylindrical, pale green to brownish when they are still small. Mature larvae are smooth and marked with two orange, white-bordered strips on each side. Larvae range in size from 1/8 inch to 1 1/2 inches long. View images.
It seems that the adult moths blew into western New York on some storm systems in late May, and perhaps a week or two later in the North Country and Hudson Valley. From my observations, moths appear to have laid their eggs preferentially in wheat and pasture, and are now moving forward in large numbers (hence the “army” name) to mow down other fields of corn, pasture, and lawns! We are noticing caterpillars most in field crops, but in many sites they may have started in turfgrass.
Although the field crops folks have been abuzz about this problem for almost 2 weeks, I received my first call from a distraught homeowner on June 7. The caterpillars had gone through a wheat field across the road, had decimated her neighbor’s lawn and were now marching into her 5 acre property. Later that day, I was riding my bicycle in the Geneva area and noticed the pavement moving… Believe me bike rides haven’t been the same since! You can easily see large infestations at bike speed, but even driving in a car. Is the white stripe particularly marked up? Is the road slick and greasy (with smooshed caterpillars)?
Natural enemies, parasites and diseases are having a field day with the extremely high numbers of caterpillars. They will significantly reduce the impact of the next generation, but will certainly not eliminate them.
What to look for
If you are managing turf, beware! Properties bordering susceptible field crops are prime targets for the migrating large caterpillars that are on the move now. Once this batch becomes adults, all turf is fair game. So scout your lawns and golf courses. Use soap flushes (1-2 tablespoons of liquid dish soap in 1 gal. of water). If populations are caught early, they are relatively easy to control.
If the initial influx of moths laid their eggs in turf, you may notice higher populations of caterpillars near lights where the adult moths congregated and lazily laid their eggs. These will be prime areas for looking for caterpillars in the next generation, and homeowners may be able to minimize infestations by leaving lights off at night when the moths are flying again in a few weeks.
Armyworms are affected by endophytically enhanced grasses. If chlorantraniliprole (Acelepryn) was applied to protect the grass from grubs and other insects, you will also be in luck. Otherwise, you will likely need to apply an insecticide to protect the grass. Many products available for use on turfgrass in New York State kill caterpillars. Acelepryn will still be effective if applied now (and will give season-long insect control). Several pyrethroids such as lambda-cyhalothrin and deltamethrin will work well with quick knock down. Beware that pyrethroid applications typically result in a lot of dead caterpillars on the grass surface, which in high populations can really stink! Spinosad will also be effective, and should be used at the high rate for large (>1 inch) caterpillars, and is available in organically-approved formulations. Bt products may be effective.
Saving the lawn
If armyworms have already ravaged a lawn, the grass will probably come back. Watering the lawn to cool it down and protect the crowns from baking in hot weather will increase your likelihood of regrowth.
Walt Nelson, Cornell Cooperative Extension is featured in this WHAM Channel 13 Rochester news story:
WIVB Channel 4 Buffalo story: Armyworms march one-by-one into region: wivb.com