Thus, any factor that influences grass growth rate or organic matter decomposition affects thatch accumulation. Presence of an adequate microbial population for decomposition. Turfgrass species and varieties differ in both vigor and method of spread. Cultivars of Kentucky bluegrass, tall fescue and creeping bentgrass differ in vigor and in their contribution to thatch. Thatch Accumulation for Kentucky Bluegrass, Tall Fescue, and Creeping Bentgrass Cultivars.
Pesticides decrease microbial populations.
Earthworms are active in organic matter decomposition and some insecticides are lethal to earthworms. Fungicides not only reduce the population of beneficial microorganisms, but they also encourage vigorous turf growth by controlling turfgrass diseases. Environmental factors can decrease the microbial population and therefore increase thatch. The optimum pH for most soil microorganisms is 5.0 to 7.0. If the pH falls below 6.0, microorganisms are unable to decompose plant tissue.