Thatch Development and Other Effects of Preemergence Herbicides in Kentucky Bluegrass Turf 1

Preemergence herbicides have been used extensively on turf in recent years to prevent annual weed development. Applications of these herbicides have been suspected of causing reduced turfgrass quality. The purpose of this study was to determine whether repeated use of preemergence herbicides resulted in thatch development and other effects associated with turfgrass deterioration. Six preemergence herbicides were applied annually for 4 years to ‘Kenblue’-type Kentucky bluegrass (Poa pratensis L.) growing on an Aquic Argiudoll (Flanagan silt loam). Calcium arsenate and bandane (polychlorodicyclopentadiene) applications were associated with increased leaf spot (Helminthosporium vagans Drechel.) disease, higher wilting tendency, reduced shoot and root growth, and substantial thatch development. The thatching tendency was associated with a complete lack of earthworm (Lumbricus terrestris Linn.) activity in the underlying soil. Bandane residue was largely confined to thatch while calcium arsenate was more generally distributed throughout the upper thatch-soil profile. Verdure was significantly reduced in plots treated with bensulide [0,0-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] while benefin (N-butyl-N-ethyl-α,α,α,-trifluro-2,6-dinitro-p-toluidine) D C P A (dimethyl tetrachloroterephthalate) and siduron [l-(2-methylcyclohexyl)-3-phenylurea] treatments, produced no measurable effects.