Minimizing Poa Annua Invasion During Kentucky Bluegrass Fairway Conversion Using Mesotrione.

A field study evaluated the best mesotrione application rates and timing to minimize Poa annua invasion when renovating to a Kentucky bluegrass fairway.

‘Rush’ and ‘Award’ Kentucky bluegrass (Poa pratensis L.) were seeded on 16 September 2008 and 4 September 2009 in Post Falls, ID.  Glyphosate (1.25kg a.i. ha^-1) was applied one week prior to seeding.  Mesotrione was applied at 0, 0.14, or 0.28kg a.i. ha^-1.  Application timing included 1) 0.14kg a.i. ha^-1 at day of seeding (DOS), 4 weeks after seeding (WAS), 5WAS, and 6WAS; 2) 0.14kg a.i. ha^-1 at 4WAS, 5WAS, 6WAS, and 7WAS; 3) 0.28kg a.i. ha^-1 at DOS and 5WAS; 4) 0.28kg a.i. ha^-1 at 4WAS and 6WAS.  Data collected included percent Kentucky bluegrass, percent Poa annua, percent bare ground, Kentucky bluegrass color, and Poa annua color.

Overall, following fall mesotrione applications, treatments that yielded the greatest percentage of Kentucky bluegrass in the spring occurred with lower rates, but more frequent applications.  Specifically, applying mesotrione at 0.14kg a.i. ha^-1 at DOS, 4WAS, 5WAS, and 6WAS yielded 59% greater Kentucky bluegrass than 0.28kg a.i. ha^-1 applications at DOS and 5WAS.  Similarly, mesotrione applied at 0.14kg a.i. ha^-1 at 4WAS, 5WAS, 6WAS, and 7WAS had 61% greater Kentucky bluegrass than 0.28kg a.i. ha^-1 applications at 4WAS and 6WAS.  Meanwhile, control plots had greater than 80% Poa annua, while mesotrione applied at lower rates with more frequent applications had less than 20% Poa annua.

Results suggest that a fairway conversion to Kentucky bluegrass is possible with minimal Poa annua the following spring when mesotrione is applied at the correct rate and frequency.