Introduction:

As the seasons begin to change, so does bermudagrass in the transition zone of Virginia. Cooler weather brings in signs of winter and forces bermudagrass into dormancy. Common golf course management practices for dormant bermudagrass is to overseed with perennial ryegrass, providing green color and playability year round in the transition zone. Mature perennial ryegrass shades bermudagrass stolons and competes for nutrients and other resources, limiting bermudagrass growth in the summer. In areas of the transition zone where temperatures are adequate for both bermudagrass and perennial ryegrass growth during the summer, transition herbicides may be used to eliminate unwanted perennial ryegrass, providing desired bermudagrass turf. Depending on location, maintenance budget, personal, and cliental expectations, determining the proper transition mechanism is important for an effective transition.

Surface Water Runoff Concerns:

Recent registrations of MonumentÔ (trifloxysulfuron sodium) RevolverÔ (foramsulfuron), and TranXitÔ (rimsulfuron) for control of cool-season turf in bermudagrass increased the selective weed control options for transition herbicides. Golf course superintendents and turfgrass managers can now choose herbicides that can fit their individual situation, offering more control with regards to timing, application rates, and sequential applications to provide the fastest, most unnoticeable transition. As a result of previously documented observations and data concerning surface water runoff injury to non-target turf, trials were initiated to determine if the newly released herbicides showed similar surface mobility compared to products already on the market. Acquiring data about the potential problems associated with herbicidal runoff provides valuable information to golf course superintendents and turf managers who are deciding on which chemicals to use in transitioning their overseeded turf back to bermudagrass. Knowledge about the potential injury involved will also dictate when applications should be made and at which rates are most effective, while reducing potential risks of mobility.

Methods:

Five transition-assisting herbicides were evaluated for injury to perennial ryegrass: KerbÔ (pronamide), ManorÔ (metsulfuron), MonumentÔ (trifloxysulfuron sodium), and TranXitÔ (rimsulfuron), and Flazasulfuron 25DF (flazasulfuron). Field studies were conducted in Blacksburg, VA 2003 and Charlottesville, VA in 2004. Chemical treatments were applied when soil was at or near soil water field capacity, on uniform slopes of approximately 7 to 11%. All herbicides were applied at label recommended rates for golf fairway transition. Irrigation or natural rainfall occurred within 4 hours of treatment at both locations.

Results:

MonumentÔ, TranXitÔ, and ManorÔ did not injure perennial ryegrass as far down slope as KerbÔ or Flazasulfuron 25DF. Herbicide mobility increases with increased soil saturation levels and herbicide rates. For example, Flazasulfuron 25DF injured perennial ryegrass twice as far down slope when applied at twice the recommended rate. Both sites in these studies were saturated with water four hours prior to herbicide treatment (a worst-case scenario). Regional data and superintendent observations indicate that areas of thin bermudagrass base or that are compacted tend to be more prone to contributing to herbicide movement in surface runoff water than thick well maintained bermudagrass. Thus, be particularly careful when treating roughs on the up slope that are along cart paths. These areas are typically compacted and may contribute to lateral herbicide mobility.