Poa annua Is Starting To Get Nervous

By Larry Gilhuly, director, Northwest Region
August 27, 2012

Human beings have walked on the moon. Computers have taken over how we communicate and many other aspects of our lives. But selective control of Poa annua in bentgrass putting greens still does not exist – at least not yet.

Those who have read my article, FLOG - What Turfgrasses Would Call It If Given A Choice, know that I suspect turfgrass plants speak to each other. I’m convinced the main topic of discussion these days among Poa annua plants is a new chemical - methiozolin. So why is Poa annua nervous, even in the near ideal growing environment of the Pacific Northwest? Early experimental use of methiozolin indicates the future could be very interesting regarding Poa annua reduction on bentgrass putting surfaces.

There have been many products available for the reduction of Poa annua, but none have successfully and consistently removed this grass from bentgrass greens. Methiozolin, a new entry into the anti-Poa annua crowd, is being tested at several universities with tests going out at over a dozen golf courses in the Northwest Region. This product may have exactly what is desired for removing Poa annua from any established turfgrass surface.

Results at Washington State University were viewed earlier this year and recently confirmed by Todd Lupkes, superintendent of the Palouse Ridge Golf Course at WSU, and Charles Golob, research associate in the WSU turfgrass management program. The material appears to be very effective in removing Poa annua slowly from bentgrass greens with three applications spaced approximately two weeks apart. Very little turf discoloration and no bare areas were noted. How can that be? Apparently it has everything with how the chemical selectively interacts only with Poa annua by disrupting the cell wall biosynthesis. As a result, the Poa annua plants cannot compete with the actively growing bentgrass.

What about the Poa annua seeds lurking in the soil profile waiting to germinate? This is where this chemistry becomes very interesting. Based on greenhouse studies completed at WSU, methiozolin also has very distinct preemergence characteristics. For this reason, golf courses with high percentages of Poa annua are not good candidates for the trial use of this product. The sites granted EUP’s (Experimental Use Permits) beginning in the fall of 2013 or the spring of 2014 have very high bentgrass/fescue populations. However, there is at least one exception to this conservative approach. Wildhorse Resort in Pendleton, Oregon has as much as 40 percent Poa annua on their greens and Superintendent Sean Hoolehan is working with the product. Will it leave bare areas or slowly transition back to creeping bentgrass? Based on my personal observations after visiting Wildhorse in late July, I’m thinking the latter.

When the individual research plots on the practice green were first viewed at Wildhorse (whose greens were originally planted to Providence bentgrass) there was no discernible color difference between the plots. From the four check plots to the four with the highest rates, and every combination in between, there was no discernible color difference approximately one month after the last application. However, when we referred to the plot plan describing the location of each plot in the research study, there was a noticeable overall reduction in Poa annua in the four plots with the highest rate of methiozolin. This was easily noticeable since Sean has also instituted a Trimmit® program. The reduced growth and minor discoloration from the Trimmit® applications was the perfect visual comparison to the differences noted between the various methiozolin plots.

Even though all of the Poa annua had not been removed from the plots treated with the highest rate of methiozolin, the reduction in Poa annua was obvious when compared to the other plots. The question now is, “Will this occur as smoothly at other golf courses in the future?” While that remains to be seen at least in the Pacific Northwest the Poa annua is beginning to get nervous.

Larry Gilhuly has spent the last 29 years making Poa annua feel both comfortable and nervous at golf courses throughout the western states. He and his fellow agronomist Derf Soller would be happy to do the same at your golf course. Contact them at lgilhuly@usga.org or dsoller@usga.org on this or any other topic related to your golf course maintenance program.

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