Impact of Sulfonylurea Herbicides on Seeded Bermudagrass Establishment and Cold Temperature Influence on Perennial Ryegrass Response to Foramsulfuron

Advancements in cold tolerance of seeded bermudagrass and introduction of sulfonylurea herbicides have given turf managers new tools. Seedling bermudagrass response to sulfonylurea herbicides applied before or soon after seeding has not been characterized. Field observations have indicated that variability exists among sulfonylurea herbicides used for perennial ryegrass control. Objectives of the conducted research were to evaluate sulfonylurea herbicides for safety and utility while establishing seeded bermudagrass, and to elucidate variability in perennial ryegrass control with foramsulfuron. Field experiments were conducted in Blacksburg, VA to assess turfgrass and smooth crabgrass response to flazasulfuron, foramsulfuron, metsulfuron, rimsulfuron, sulfosulfuron, and trifloxysulfuron-sodium, applied 1 and 3 weeks after and before seeding. Herbicides applied 3 weeks after seeding (WAS) were generally more injurious than when applied 1 WAS. Foramsulfuron, metsulfuron, and sulfosulfuron are safe to apply 1 and 3 WAS, causing no reduction in turf cover. Herbicides applied before or after seeding injured bermudagrass in the following order from most to least injurious: flazasulfuron = trifloxysulfuron > rimsulfuron > metsulfuron = sulfosulfuron > foramsulfuron. Flazasulfuron and trifloxysulfuron-sodium are not safe to use within 3 weeks of seeding, while foramsulfuron and metsulfuron can be used anytime before or after seeding bermudagrass. Flazasulfuron, foramsulfuron, and trifloxysulfuron-sodium were evaluated for perennial ryegrass control as affected by environment. Among environmental variables collected soil temperature averaged 7 DAT correlated best with perennial ryegrass response of the three tested products. Soil temperatures below 18 C perennial ryegrass reduced control 9 WAT from 78 to 31% for foramsulfuron while flazasulfuron and trifloxysulfuron-sodium efficacy were not significantly affected. Temperature dependence on perennial ryegrass control can be ranked from most to least as follows; foramsulfuron > trifloxysulfuron-sodium > flazasulfuron. Studies were conducted to determine absorption and translocation of 14C flazasulfuron when applied to perennial ryegrass roots or foliage. Roots treated with 14C flazasulfuron absorbed 41% of recovered 14C while 25% of 14C moved from treated roots to foliage. It appears root absorption is an important component of flazasulfuron efficacy since most of the absorbed 14C remained in treated leaves and root absorbed 14C moved rapidly to foliage.