Turf-type tall fescue cultivars may accumulate thatch much faster than older, forage-type cultivars (Leonard et al., 1987). Thatch development in turf-type cultivars is correlated positively with the total cell wall mass per unit area and verdure, a measure of the aerial shoots after mowing (Shearman et al., 1986). Crown tissue also resists decay and tends to accumulate in thatch (Lederboer and Skogley, 1967). Excessive thatch can restrict the rate of soil water infiltration severely (Baldwin et al., 2006) while supporting an abundance of insect pests (Davis, 1989).
Vertical mowing (dethatching) reduces thatch (Kopp and Johnson, 2006). Dethatching generally is recommended when the thatch layer reaches a depth of 1.27 cm (0.5 in) or more. Power rakes and vertical mowers often are used to dethatch tall fescue turfs in late winter or early spring before applying a preemergence herbicide, and in late summer or early fall before broadcasting seed.