Insect damage is often masked during periods of heat and drought in late summer. In fact, we often talk about damage from chinch bugs and sod webworms manifesting when temperatures cool and the rains come in late summer. The change in the weather causes the grass to “wake up” from summer dormancy. The insect damaged areas stay brown as the dormant turf greens up. If after the rain this week your grass does not appear to be a little more perky, then a closer look is definitely necessary. Of course, prudence suggests that one might have been paying attention all along, but better late than never!
To more fully investigate this issue conduct a soap flush: Take 2 ounces of lemon dish detergent and mix it with 2 gallons of water. Measure out a square yard of turf and pour the solution on the area. Wait 10-15 minutes and see who shows up. Soap flushing irritates the insects, so they emerge from their daytime hiding places in the thatch and soil interface. This technique works very well with webworms, armyworms, cutworms, billbugs and annual bluegrass weevils, and to a lesser degree, chinch bugs. Measuring out a square yard of turf helps to quantify the insect population, which provides data to compare to accepted damage thresholds and make reasoned control decisions.
Learn more here: Cornell Turfgrass Short Cutt.