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. Compact, poorly drained soils 1ack the oxygen necessary for these microorganisms. Extreme high temperatures and dry conditions also decrease microbial population. Soils with very low organic content can't support an active microorganism population.