Hi,

We are getting numerous reports of fall armyworm activity in several areas of Maryland. This pest is native to North America and recent weather has provided the perfect conditions for an outbreak in the eastern and mid-western United States. It is a sub-tropical insect that in its adult stage (a moth) “flies” north, carried with the help of wind currents.

As of late August, we were seeing caterpillars in the later instar (more mature) stages. They have a distinct inverted “Y” on their head. They are very difficult to control at this stage. And they will be pupating in the soil shortly. Control measures at this point are not recommended.

Fall armyworms feed on the leaf blades of turf, but the grass may generate new growth if the crown portion is not too damaged. With leaf blades chewed off, the turf crowns become more susceptible to heat/drought, which can kill the plants. Providing irrigation will help protect the crown and grass can recover if it still has a healthy growing point.

You can overseed and fertilize now -- it is the ideal time to do so for cool-season lawns -- but then you will have to monitor your new turf closely, check for a possible next generation of armyworms later this fall, and determine whether control measures are necessary.

A “drench test” is a method to monitor for fall armyworms. Mix 3-4 tablespoons of dishwashing liquid in 2 gallons of water. Pour this evenly over 1 square yard of turf. Watch the area for 10 minutes and count the caterpillars as they rise to the surface. Fall armyworm populations above 9 per square yard may warrant treatment.

Fall armyworms are more effectively controlled when the caterpillars are young and small -- greenish in color, less than 3/4". If you are seeing many fall armyworms (above 9 per square yard) in that stage, a lawn insecticide containing Bacillus thuringiensis, Spinosad or Acelypryn will kill the small caterpillars (@ <¾” size). Acelepryn (Chlorantraniliprole) is found in GrubEx (active ingredients can change periodically so check the product label). Read and follow all instructions for the product you choose.

Jon

You're welcome.