Preemergence Weed Control in Seeded Bermudagrass Stands 1

Weed competition is a major cause of poor bermudagrass ( Cynodon dactylon (L.) Pers.). stands established from seed. Two separate experiments were undertaken to find a selective preemergence herbicide to minimize weed competition when establishing bermudagrass from seed. In a greenhouse experiment, four preemergence herbicides, each at four rates were applied to three bermudagrass hybrids in two soil types, a Kirkland silt loam (Thermis Uderic Paleustoll), and a Doughtery loamy sand (Thermic Arenic Hoslustalf). After 3 weeks the germinated and growing seedlings were counted. A highway cut slope was the site of the field experiment which consisted of two Preemergence herbicides (terbutryn and metribuzin) applied to four, seeded, bermudagrass strains. Phytotoxic effects of the herbicides on emergence of the bermudagrass and estimates of weed populations were made at 30‐day intervals. Analyses of the greenhouse data indicated metribuzin and terbutryn were relatively non‐toxic to bermudagrass. Oxadiazon and siduron were highly toxic, and eliminated from further consideration. No significant differences were found among rates for any of the herbicides. The bermudagrass cross, Guymon × 10978, had significantly greater germination than the other bermudagrass with optimum germination observed in a Kirkland silt loam soil. Common bermudagrass germinated the quickest and provided the most dense cover of all bermudagrass types used in the field experiment. Greater weed control was obtained with terbutryn than metribuzin. The application of terbutryn at 2.71 kg/ha was the most toxic treatment to the bermudagrass. Terbutryn at 1.36 kg/ha provided good weed control at an acceptable level of toxicity.