Impacts of Preemergence Herbicides on Hybrid Bermudagrass Morphology

Preemergence (PRE) herbicides were evaluated in multiple experiments to determine their impacts on hybrid bermudagrass morphology [(C. dactolyn (L.) Pers. x C. transvaalensis (Burtt Davy)]. First, indaziflam and prodiamine were applied to hybrid bermudagrass rooted to various depths in either sand or silt loam mini-rhizotrons. Results indicated that prodiamine (a mitiotic inhibitor) and indaziflam (a cellulose biosynthesis inhibitor) both significantly reduced root length density compared to a non-treated control; however, indaziflam treated plants exhibited foliar injury (i.e., reddening, necrosis) while those treated with prodiamine did not.

The researchers surmised that reductions in root length density with indaziflam may compromise macro- or micronutrient accumulation in foliar tissue, thus explaining the foliar injury observed in initial work. Glasshouse experiments were conducted in hydroponic culture evaluating effects of PRE herbicide treatment on hybrid bermudagrass nutrient content. Similar to previous studies, both indaziflam and prodiamine reduced hybrid bermudagrass root growth, with indaziflam treatment also resulted in foliar injury. Nutrient analysis showed that indaziflam reduced magnesium (Mg) and manganese (Mn) compared to non-treated controls, potentially explaining the foliar injury observed.

Additional mini-rhizotron studies were conducted to determine the effects of organic matter content on hybrid bermudagrass tolerance to indaziflam. Plants were established in sand-rootzones varying in organic matter content (0.000, 0.003, 0.007, and 0.012 kg kg^-1 [kilogram per kilogram]). Foliar injury with indaziflam was reduced as organic matter content increased; moreover, reductions in root length density with both indaziflam and prodiamine were less pronounced in soils containing more organic matter.

Lastly, a field study was undertaken to determine the influence of PRE herbicides on hybrid bermudagrass divot resistance and recovery. Plots were subjected to the factorial combination of seven herbicide treatments (indaziflam at 35 and 52.5 g ha^-1 [grams per hectare]; prodiamine at 840 g ha^-1; pendimethalin at 3360 g ha^-1; dithiopyr at 560 g ha^-1; oxadiazon at 3360 g ha^-1; untreated control) and three divot timings [1, 2, and 3 months after herbicide treatment (MAT)]. Under the conditions of this study, applications of PRE herbicides at labeled rates did not affect divot resistance or recovery.