The Fate of Diazinon Applied to Thatched Turf

Diazinon (O,0-diethyl·0-(2-isopropyl"6.methyl-4-primidinyl) phosphorothioate) is widely used to control turfarass insect pests. Poor control of soil-inhabiting insects has been found where diazinon has been applied to thatched turfgrass stands. The purpose of this study was to evaluate the environmental fate of diazlnon applied to turfgrass stands. A microecosystem was used to follow the fate of radiolabeled diazinon surface applied to Kentucky bluegrass (Poa pratensis L.) turfs, with or without a thatch layer, growing on Flan­ igan silt loam (fine, montmorillonjtic, mesic Aquic Argiudoll) irri­ gated daily or every 4 days. Loss of diazinon by volatilization, leach­ ing, and degradation accompanied by release of14C02 or incorporation of label into soil compounds was measured. The most degradation of parent compound occurred on turf containing a thatch layer ir­ rigated daily where only 7% of the applied dlazinon remained after 3 weeks. Between 32 and 47% of the parent compound remained in either turf with thatch irrigated every 4 days or turfs without thatch. The majority of the dlazinon (96%) remained in the top 10 mID of the turf profile regardless of whether this was thatch or soil. In the presence of thatch, there was an accelerated rate of dlazlnon deg­ radation as measured by release of I4C02 from the two position on the pyrmidine ring. Increasing irrigation frequency on the thatched turf did not cause an increase in leaching but did increase diazinon breakdown. The results of the study suggest that where thatch is present, reduced control of insects is due both to a failure of the insecticide to move through the thatch and an increased rate of deg­