Armyworms: What Are They and Should You be Worried?

Written by Greenwise Team
Published on July 18, 2018
We are starting to see something new this year… Armyworms. This is the first year where we are seeing Armyworms impact our lawns. Part of the reason is our cool, wet spring, which favors their development. We may also be seeing them because of our warmer winters, which means they are moving farther north than they used to. What’s crazy is how quickly Armyworms can decimate a lawn. It can literally happen overnight. Here’s the good news. Armyworms don’t eat the root system of turf grass, just the crowns, which means your grass will recover with watering, fertilization, and reseeding. We are investigating effective, safe treatments to resolve this issue and will keep you posted. Please call us to evaluate your lawn at 847.866.1930. For more information on Armyworms, read the excerpt below from Purdue Extension: Turfgrass Insects. ABOVE-GROUND PESTS Armyworms Armyworms are the immature stage (larva/caterpillar) of several widely distributed moth species. Species most often associated with turfgrass include the common armyworm Mythimna unipuncta (Fig. 8), fall armyworm Spodoptera frugiperda (Fig. 9), and yellow-striped armyworm Spodoptera ornithogalli. These insects are better known as pests of agricultural crops, but they sometimes infest turfgrass, especially in areas that border agricultural fields or unmanaged areas such as ditches or fencerows. Outbreaks in turf tend to be patchy and sporadic but sometimes occur on a larger scale. As their name implies, armyworms may occur en masse and can migrate across large areas of turf, cutting it down to crown level as they go. Because they often go unnoticed while they are small, the turf may seem to disappear almost overnight once these insects reach a larger size. Small patches of brown and overall ragged appearing turf are more typical symptoms. Fortunately, unless the turf is severely stressed by drought, it generally recovers well with irrigation or rainfall and adequate fertility.
Figure 8. Common armyworm caterpillar with lengthwise brown and/or yellow stripes.
Figure 9. Fall armyworm caterpillar with lengthwise stripes and inverted Y-shape on head. (Photo Credit: J. Obermeyer).