SWEET VERNALGRASS CONTROL IN COOL SEASON TURF. A.N. Smith* and S. Askew, Virginia Tech, Blacksburg, VA (10)


   Sweet vernalgrass (Anthoxanthum odoratum)  is a perennial grass weed found in cool-season turfgrass. It is highly competitive in the spring due to its rapid growth, early flowering, and potential allelopathic suppression. Sweet vernalgrass also has a high potassium requirement. It can easily adapt to new environmental conditions; research has shown that significant differences in morphologies, flowering dates, and seed yields have occurred due to genetic adaption to new environments. Sweet vernalgrass is very difficult to control. An experiment was conducted near Richmond, Virginia to determine herbicide options for sweet vernalgrass control in cool-season turf. Seven herbicide treatments were evaluated. At 34 DAT, MSMA at 2.1 kg a.i. ha-1, mesotrione applied once at 0.28 kg a.i. ha-1, and mesotrione applied twice at 0.14 kg a.i. ha-1 controlled sweet vernalgrass 73, 63, and 57%, respectively. At 71 DAT, control by MSMA declined to 40%, whereas mesotrione applied once and mesotrione applied twice controlled sweet vernalgrass 67 to 100%. Rapid growth of sweet vernalgrass in the spring might explain why mesotrione applied once provided the best control as this herbicide tends to be more effective during rapid growth phases of susceptible plants. Applying more active ingredient during sweet vernalgrass peak growth seems to play an important role in its control. Decline of MSMA control can likely be explained by MSMA’s contact activity and the perennial nature of the weed. Fenoxaprop, quinclorac, amicarbazone, methiozolin, and sulfentrazone did not control sweet vernalgrass.