Influence of Thatch on Preemergence Herbicide Activity in Kentucky Bluegrass (Poa pratensis)Turf

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Abstract
The effects of five preemergence herbicides on turfgrass quality and control of crabgrass (Digitariaspp.) were measured to determine the influence of thatch on preemergence herbicide activity in Kentucky bluegrass (Poa pratensisL.) turf. Field applications of benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin -5-one], and prosulfalin {N-[[4-(dipropylamino)-3,5-dinitrophenyl] sulfonyl]-S,S-dimethylsulfilimine} to thatchy Kentucky bluegrass turf in spring caused injury that was apparent during periods of summer stress, while DCPA (dimethyl tetrachloroterephthalate) and bensulide [O,O-diisopropyl phosphorodithioateS-ester withN-(2-mercaptoethyl)benzenesulfonamide] caused little or no injury. The same treatments on thatch-free sites revealed that only prosulfalin was injurious. Adsorption of benefin, bensulide, and DCPA from solution was greater by thatch than by soil; however, the mobility of these herbicides in undisturbed thatch profiles was greater than measured in undisturbed surface soil from thatch-free sites. Thus, turfgrass injury from preemergence herbicides on thatchy sites is due to at least two factors: the greater mobility of preemergence herbicides in thatch than in soil; and the inherent susceptibility of Kentucky bluegrass to injury from preemergence herbicides that come into direct contact with roots and other absorbing organs.