Brown, discolored, or dying grass can be a sign of all sorts of lawn problems including summer patch and dollar spot and other common lawn diseases, grubs, drought stress, and improper lawn care just to name a few, however, there are generally more signs that appear when you have (or already suffered from) an armyworm infestation.
6 signs of army worm damage
Discolored grass that lays flat
Brown patches, especially along the perimeter, making their way inward
Chewed, jagged grass tips or transparent segments in grass blades
Bald spots, where they’ve eaten entire grass plants down to the soil
Increased or unusual bird activity on your lawn
Movement: Your lawn may look like it is moving on its own