Golf Course Maintenance- June 15, 2012by Fred Biggers, CGCS, Golf Course Maintenance Director
Poa Annua, Bentgrass and Growth Regulators
“What they are, and how do we use them to improve our Greens?”
Greens and their ultimate quality are a complicated subject and putting conditions are all affected by a number of factors. One of the largest influences on putting green quality is the use of growth regulators. The use of growth regulators is largely influenced by the grass variety blend on the greens.
At Devils Knob the greens were seeded to Pencross Creeping Bentgrass in 1974. They have been a mixture of approximately 50% Bentgrass and 50% Poa annua for many years. Some greens are as much as 70% Poa Annua because of their micro climate which favors cool or shady conditions which favor the growth requirements of Poa Annua. Fortunately these greens have been consistently reliable smooth, quick putting surfaces helped greatly by the cool weather conditions at 3,300’ to 3850’ feet of elevation.
At Stoney Creek the greens on the original 18 holes (Monocan-Shamokin nines) are a mixture of creeping Bentgrass, and Poa Annua. These greens were originally seeded to Pencross creeping bentgrass in 1986-7. Over time the Poa Annua (a low growing, self seeding weedy grass) invades the greens surfaces by having seeds track in on golf shoes, or mowers etc., finding a place to germinate like recent unrepaired ballmarks. Greens grass populations can shift 2-5% per year from Bentgrass to Poa Annua.
After 25 years you can see how the population percentage of Poa Annua in the original 18 greens is somewhere between 40% and 70% Poa Annua. The next interesting fact about Poa Annua as a greens component is that not all Poa Annua varieties are created equal (in appearance!). There are two different types of Poa Annua- Annual and Perennial. Most older greens have significant patches of perennial Poa Annua, which in most cases, completely dominates most of the older Bentgrass varieties. Perennial Poa Annua also does not produce many seedheads which makes it more attractive in blends with Bentgrass. Several of our greens like- Monocan #1 and #5, have large populations of perennial Poa Annua which have persisted very well through many years of intense heat and drought.
Shamokin green Poa-Bent mix with seedheads
We use several different Growth regulators on our greens at Wintergreen. In the early springtime we apply Embark T & O (Mefluidide) on the greens at both Devils Knob and Stoney Creek. The Embark T & O growth regulator helps to prevent the formation of Poa Annua seedheads on the Greens surfaces. Usually the plan of attack is to apply Embark T&O somewhat early before seedheads get visible so a high a percentage of control is achieved. Typically two to three applications of Embark are made at 3 week intervals each course. At Devils Knob after mid May we switch to Primo (Trinixapac Ethyl) and apply it biweekly to the greens to slow down the rate of growth and to promote a lateral growth habit over a more vertical growth habit. At Stoney Creek after two applications of Embark T-O in March-April, we switch growth regulators to Cutless (fluroriprimidol) mixed with Primo which favors the growth of the Bentgrass in a green over the growth of the Poa Annua. The Cutless growth regulator dramatically lowers the canopy height of the Poa Annua and helps it to blend in with the Bentgrass. It also somewhat stunts the growth of the Poa Annua and favors the increase spreading of Bentgrass into the Poa Annua areas. We continue the use of the Cutless/Primo combination until extremely hot weather sets in, usually in July.
Monocan green Poa-Bent mix with seedheads
Recently there has been an exciting new development in Poa Annua research which luckily has involved us here in Virginia. Dr. Shawn Askew of Virginia Tech has become heavily involved in the testing of a new Herbicide -Methaziolin ( soon to be known as Poacure) which was developed by a Cornell University educated Korean, Dr. Song Lee. He has formed a new company to develop this product and bring it on the market both in Korea and Japan but to also bring it into the American market. Dr. Askew has done most of the research in conjunction with a fellow Turf Reseacher from Auburn University. This exciting new herbicide, Methiazolin, can completely eliminate small populations of Poa Annua from greens similar to our Tuckahoe greens with less than 10% Poa Annua populations with just four to eight applications in a single year’s time. On greens like ours on the Monocan and Shamokin nines with extensive Poa Annua populations of 40% or greater, Dr. Askew of Virginia Tech thinks that complete control will be better achieved through a more gradual approach to rates and timing of Methaziolin over a two to three year time period. A likely scenario would be Poa Annua % (start) -60%, (after one year-six to eight applications) -20% Poa Annua, (after two years- six to eight applications )->5% Poa Annua, (start of third year- three to four applications)- >1% Poa Annua. Another side benefit of Methiazolin is that it also inhibits the growth and germination of Goosegrass and also prevents the germination of new Poa Annua seedlings. A spring application of Methiazolin has a six month effect on weed germination from just a single application.
Practice Putting green less than 10% Poa population
If we were to initiate a Methiazolin program we could renovate our greens by eliminating Poa Annua and Goosegrass and, at the same time establish new improved varieties such as 007 and Mackenzie (like on the Tuckahoe greens) by interseeding our greens Spring, Summer and Fall with these “better” bentgrasses. We have made an application to participate in the Methiazolin EUP program starting this coming fall and have heard back from Dr. Song Lee from the Moghu Research Center in Korea. More to follow.
Tuckahoe green less than 5% Poa population
As of this writing in early June the greens at Stoney Creek have now lost most of their seedheads, and we are beginning to lower our cutting heights down to a .120 bench setting which should result in an actual height of cut of less than .100 of an inch. It’s as low as we can go with our greens mowing equipment. We will be staying on our Cutless/Primo growth regulator program until the temperatures rise mid-summer. Our hope is to vibratory roll greens at Stoney Creek two to three times per week which will result in smoother, quicker, more consistent greens. At Devils Knob the same things apply except we don’t do as much rolling due to labor restrictions and also the fact that DK’s greens have much more severe contours than the greens at Stoney Creek.
I hope that this article on the technical side of Bentgrass Putting green management has been helpful to your understanding of how your greens putting conditions are actually dependent on many different factors such as temperature, moisture, time of year, growth regulator usage, mowing height and frequency, rolling, and fungicide use. Although I can decide what to do each day on the greens, the one thing that I haven’t figured out yet is how to control the weather!
