Frequency of Herbicide Treatments for Summer and Winter Weed Control in Turfgrasses

Abstract

Four herbicides were applied in the spring and fall over a 3-yr period to Kentucky bluegrass [Poa pratensis (L.) ‘Common′] in the Mountain Region and bermudagrass [Cynodon dactylon (L.) Pers. ‘Common′] in the Piedmont Region of Georgia at different frequencies of treatments for summer and winter weed control. Large crabgrass [Digitaria sanguinalis (L.) Scop.] was controlled throughout the 3-yr period from spring treatments of bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] at 11.2 kg/ha and oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] at 4.5 kg/ha in the first year followed by 5.6 kg/ha for bensulide and 2.3 kg/ha for oxadiazon the following 2 yr. To control large crabgrass with benefin (N- butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) it was necessary to apply 3.4 kg/ha for 2 consecutive yr before rates could be reduced to 1.7 kg/ha. Oxadiazon was the only herbicide that controlled goosegrass [Eleusine indica (L.) Gaertn.] completely. Control was excellent throughout the 3-yr period when oxadiazon was applied at full rate in the spring of the first year with no additional treatments during the following 2 yr. Optimum control of winter weeds was obtained throughout the 3-yr period when herbicides were applied at full rates for the spring and fall treatments the first year followed by one-half rates at similar dates the following 2 yr. Bensulide treatments increased cover of corn speedwell (Veronica arvensis L.) and hop clover (Trifolium agrarium L.); DCPA (dimethyl tetrachloroterephthalate) and benefin increased spur weed (Soliva spp.) and wild parsnip (Pastinaca sativa L.); and oxadiazon increased wild parsnip and thymeleaf sandwort (Arenaria serpyllifolia L.).