Fall Applications of SP25052 for the Control of Dallisgrass.

Field trials were conducted at Meadowbrook Golf Course in Lubbock, TX during the fall of 2010 to evaluate the efficacy of SP25052 for dallisgrass control. Studies were conducted on mature dallisgrass infestations present in a hybrid bermudagrass rough. Treatments were initiated on September 27, 2010 or October 21, 2010 and consisted of single or sequential applications of SP25052 (93 or 137 g ai ha^-1) + MSO (0.5% v/v) + AMS (2% w/v). Sequential applications of foramsulfuron (106 g ai ha^-1), foramsulfuron (106 g ai ha^-1) + [dicamba + iodosulfuron + thiencarbazone (174 g ai ha^-1)], and an untreated control were added for comparison. Visual estimates of percent dallisgrass cover and bermudagrass phytotoxicity were recorded every two weeks until early December. Dallisgrass regrowth (% cover) the following spring was recorded every two weeks until mid-June. Percent dallisgrass cover was converted to percent dallisgrass control by comparing each plot to the cover recorded at initial herbicide application. Single applications of SP25052 applied in October exhibited 44 to 61% dallisgrass control 37 weeks after initial treatment (WAIT), while single applications of SP25052 applied in September exhibited 86 to 94% dallisgrass control 37 WAIT. Sequential treatments of SP25052 exhibited similar control (94 to 95%) to single applications of SP25052 at the high rate applied in September. Sequential applications of foramsulfuron alone exhibited unacceptable dallisgrass control (58%) 37 WAIT, while foramsulfuron + dicamba + iodosulfuron + thiencarbazone exhibited 94% dallisgrass control 37 WAIT. Results from this trial suggest that timing is critical when making applications of SP25052 for dallisgrass control in the fall. September applications provide excellent control of dallisgrass while waiting until October to make applications may result in poor control. The tank-mixing of foramsulfuron with dicamba + iodosulfuron + thiencarbazone also provides excellent dallisgrass control when initial applications are made in September.