The most recent chemical control for Poa annua control labeled for sports turf managers is mesotrione with the common name Tenacity. Tenacity just became available in the spring of this year for athletic fields.

Using Tenacity for Poa annua control

Most field managers deal with Poa annua annually. Some have chosen to embrace it, but most have declared a war that will never end. Like most things in this world, new technologies become available all the time. The most recent chemical control for Poa annua control labeled for sports turf managers is mesotrione with the common name Tenacity. Tenacity just became available in the spring of this year for athletic fields. The following information is how the three of us used Tenacity in slightly different ways to help with the never ending fight against Poa annua. 

Tim VanLoo, CSFM, Iowa State

At Iowa State University we used Tenacity on Jack Trice Stadium and Johnny Majors practice football facility, both sand-based fields. I worked with Syngenta’s territory manager, Luke Dant, to come up with a plan. Knowing that Tenacity has post and pre-emergent capabilities, we formulated a plan that we thought could use both of the chemical’s attributes to our advantage.  Tenacity has a limit of 16oz/acre/year.

Luke and I decided to make four applications at a 4oz/acre rate on 10-day intervals starting the first week of May. Applying in this matter would give me 50-60 days of pre-emergent control in the spring while controlling the Poa annua that was in the fields already. Using Tenacity also allowed me to re-seed the worn areas from the previous playing season. I was able to germinate Kentucky bluegrass during the applications without any problems.

We were able to get complete control in Jack Trice stadium and greatly reduce the amount of Poa annua in the practice field. The Poa annua spots that were in the stadium were very small in size. The areas in Johnny Majors that still have Poa annua were 1-2 feet in diameter. Now those spots have been reduced greatly and have some desired grasses growing inside the spots. I think that Tenacity applied in the spring of 2011 should take out most of the remaining. Tenacity had no affect on Kentucky bluegrass color or growth during the applications. Tenacity did turn perennial rye grass off color during the applications, but did not kill it. Once the applications were complete the perennial ryegrass came back to normal color. Tenacity also killed clover and other broadleaf weeds that were present in the practice field.   

For the spring of 2011, I plan on doing the same plan except I am going to shorten my intervals to 7 days. I think this will help eradicate the Poa annua that is still there and give adequate pre-emergent control. 

Eric Adkins, CSFM, Toyota Park, Chicago

After years of trying to get rid of Poa annua my efforts just weren’t good enough. I have tried all kinds of products to slow the growth rate, limit seed head production and outright kill it. There has been some success in my efforts but nothing as good as using Tenacity.

Here at TOYOTA PARK there are two grass fields both 100,000 square feet in size. So I decided to make a guinea pig out of the practice field, which has more Poa annua than the game field. I consulted with others that have used Tenacity and bought a gallon. After I got over the shock of the price, $760 a gallon, I made my first of five applications. I carefully measured out 2 ounces of product and made my first application on August 6 and my last application on August 24. My total use of product was 10 ounces at roughly six dollars per ounce for a grand total of $60. That’s very inexpensive in my book to Poa annua. As of October 1 my practice field is Poa annua-free for the first time since the sod was laid in October 2006.

I would mention that it may not be the best timing to use herbicides in the middle of August, but in my case I didn’t see any harm to the desirable bluegrass or the ryegrasses. Tenacity for me was very safe to use during the hot summer months. Another thing that Tenacity did was to wipeout all my weeds, dandelions, plantain, clover, and crabgrass too. I plan on doing this again in mid to late spring next year, just to clean up any Poa annua that may be there or that has germinated in the spring.

One thing I was told is that as the plant dies it will turn white in color. I did see my weeds turn white but I couldn’t see the Poa annua turn white. As far as I can tell it just melted away and the bluegrass took over. Being that we did this to the practice field, our normal routine is to fill the divots daily. In doing that I think if there were any problems areas of Poa annua dying we handled them with our normal daily divoting. I plan on doing a late fall application on the game field starting sometime in early October.  I think as a turf manager I can finally control Poa annua cost effectively and without harming any of the desirable grass.

Amy Fouty, CSFM, Michigan State

We have battled for many years, like most in our spring and fall with the cloudy, damp climate here in Mid Michigan. I have worked with our turf department here on campus for many years, Dr. Calhoun, our weeds specialist, and his research technician, Aaron Hathway, for viable options to rid us of Poa annua and Poa Trivialis. Until this season I had been weary of the “latest and greatest” products for Poa control. I am a very conservative grass grower and have been skeptical of many products. We first conducted a trial with Velocity and Tenacity at different rates and intervals of applications in the south end zone of Spartan Stadium. We determined from these trials in the spring we could use fewer products with repeated applications.

We made our applications to Spartan stadium field in mid-June, which consisted of taking 1oz/acre rates and making five applications, one application every 3-4 days, to equal one 5oz/acre total. The repeated applications at the low labeled rate provided us with an excellent reduction of Poa annua, Poa trivialis, and Common Bermuda (on the practice football test area). Throughout the 14-day application process we seeded Kentucky bluegrass, aerated, and topdressed the playing surface. As both Poa’s browned out in weeks 3-4, we had numerous seedlings surfacing and thriving and by week 6 you could not tell we had done anything.

We reduced our “weedy grasses” significantly but not completely with these applications. The existing Kentucky bluegrass remained healthy with no reduction in root density or rhizome growth. In areas we had solid Poa annua it has been reduced by at least 50% and now has Kentucky bluegrass thriving within those areas. I believe with repeated treatments this is a great tool in the tool box to combat Poa annua and maintain safe and consistent playing conditions.

Using Tenacity positively benefited all of our fields. It is our hope that we were able to show another tool to help achieve a uniform and safe playing surface for the athletes that use our facilities. As you can see we all used Tenacity at different times of the growing season with slightly different application rates and timing. We all had great success. Please don’t hesitate to contact any of us on more details using Tenacity. 

Tim VanLoo, CSFM; Amy Fouty, CSFM; Eric Adkins, CSFM

Tim VanLoo, CSFM is manager of athletic turf and grounds at Iowa State; Eric Adkins, CSFM is sports turf manager for Toyota Park in Chicago; and Amy Fouty, CSFM is athletic turf manager at Michigan State.