SELECTIVE CONTROL OF COMMON BERMUDAGRASS IN ST. AUGUSTINEGRASS

Common bermudagrass [Cynodon dactylon (L.) Pers.] is the most troubles ome weed in commercially produced St. Augustinegrass (Stenotaphrum sec undatum (Waiter) Kuntze] sod due to inadequate selective control metho ds. Currently available herbicides are nonselective and require multip le applications, which delays replanting, and cause significant St. Au gustinegrass injury. Research was conducted to evaluate several herbic ides for selective control of common bermudagrass in 'Floratam' St. Au gustinegrass. Herbicides included ethofumesate -)2-ethoxy-2,3-dihydro- 3,3-dimethyl-5-benzofuranyl methanesulfonate] and ethofumesate plus ei ther flurprimidol [alpha-(1-methylethyl)-alpha-[4-trifluourmethoxyy) p henyl]-5-pyrimidinemethanol), atrazine yl-N'-(1-methylethyl)-1,3,5-tri azine-2,4-diamine], or siduron [N-(2-methylcyclohexyl)-N-phenylurea]. Excellent (>95%) common bermudagrass control followed sequential appli cations of ethofumesate plus atrazine applied in March, April, and May . Good control (80-89%) was observed with ethofumesate alone applied t he same months. Inconsistent and/or poor control (<70%) of common berm udagrass was obtained with ethofumesate plus either flurprimidol or si duron. Additional treatments made in February and/or in November of th e previous year did not increase control. St. Augustinegrass turf qual ity was unaffected by ethofumesate plus atrazine, Turf quality was red uced 4 to 8 wk after repeat applications of ethofumesate plus siduron. Ethofumesate plus flurprimidol combinations reduced turf quality for 8 to 12 wk. Properly timed ethofumesate plus atrazine applications is the first reported means of selectively controlling common bermudagras s in St. Augustinegrass turf.