Answer: What you describe sounds suspiciously like sod webworms. When sod webworms are present, dethatching the turfgrass may help. You can test to see if there is a large enough population to warrant control. The easiest way is to conduct an irritating drench or soapy flush. This is done by putting one or two tablespoons of lemon-scented dish detergent in one or two gallons of water and pouring the soapy solution over an area which is about two feet on each side. The caterpillars will be irritated by the solution and will wriggle out of the thatch and up to the surface, where they can be counted. Most caterpillars will respond to the soapy solution within two to five minutes. The soapy flush and the visual inspection should be conducted on the edges of the affected patches, because this is where the caterpillars will be concentrated (they will have already moved out of the centers of the dead patches). Treatment choices include parasitic nematodes and Bacillus thuringiensis (B.t.). Best wishes with your lawn.
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