As a golf course superintendent, your first challenge was convincing those who pay the bills that the old Poa annua and creeping bentgrass greens were becoming more unreliable each year due to a combination of stressful weather conditions and unreasonable expectations for fast, flawless playing surfaces throughout the season. You did your homework, presented your case and, with a little help from your friends (i.e. Green Section agronomist), you are now the proud owner (well, caretaker) of brand spanking new creeping bentgrass greens.
Then you see it! And it elicits the same feeling you get when you discover the first ding, dent or scratch on a new car. The “it” is that first small colony of Poa annua that dares to contaminate your pure stand of new and improved bentgrass and you know more will follow unless you take action. It makes you recall comments from the know-it-all golfer who questioned the sanity of those who approved the regrassing project because, after all, everyone knows Poa will ultimately dominate the putting surfaces again within a few years.
What can be done to keep Poaannua out of new greens when it is abundantly present in the fairways and roughs? Will unrepaired ball marks, aeration holes and other openings in the turf canopy present constant opportunity for Poa to contaminate the greens? More importantly, might the know-it-all soothsayer, for once, actually be right?
Well, some degree of Poaannua contamination into new greens is inevitable at old courses, especially courses in the North Central Region where conditions for annual bluegrass establishment and survival are ideal for a significant portion of the golf season. However, the amount of encroachment can be limited by employing a combination of cultural and chemical programs. For example, keeping the greens as dry as possible and making an extra effort to manage organic matter accumulation with light, frequent applications of sand topdressing will go a long way towards providing a growing environment that favors creeping bentgrass versus Poa annua.
Most superintendents would have simply reached down and physically removed that first, annoying dime-sized colony of Poaannua from the green; and hand removal is an effective early strategy for keeping new greens clean. It doesn’t take much time to have someone walk the perimeters of the greens every week or so and cull out a few Poa colonies, if you begin the process before contamination gets out of hand. Start as soon as the greens are open to play, if not before. Wait too long and an abundance of large Poa colonies will transform a simple task into a labor-intensive, time-consuming ordeal for the crew, not to mention turning the greens into Swiss cheese every week. .
Judicious use of plant growth regulators, such at Cutless and Trimmit can definitely slow down the rate of Poaannua encroachment into new greens, but they tend to be more effective at courses in locations that experience more summer heat stress versus courses in the relatively cool climate of the North Central Region. What about PoaCure, Velocity or Xonerate for Poa control in new greens? As of today, you need an experimental use permit for PoaCure, Velocity is not labeled for greens and there is no information on the Xonerate label regarding rates or timing for use on putting greens. End of discussion, for now.
Wouldn’t it be great if there were a product that had the ability not to control, but actually prevent Poaannua from becoming established in bentgrass greens? Wouldn’t it be great if that product was actually labeled for putting greens? Well, there is, but very few turf managers in this Region ever consider the use of bensulide preemergent herbicide as part of a comprehensive program to manage Poa encroachment in new greens.
Maybe bensulide is too “old school.” Then again, even Old Spice aftershave is making a comeback. Maybe the urban legend of bensulide being an insidious “root pruner” still frightens off potential users, even though research indicates no significant effect on rooting when it is applied to greens at low to moderate rates.
Granted, I would think twice about applying bensulide to a weak, shallow-rooted bent/Poa green in August when every millimeter of rooting is precious. On the other hand, am I really all that worried about a little root loss, assuming it even occurs, at a golf course in Wisconsin where the new A-4 bentgrass greens possess a mass of roots growing down 12 inches into the gravel layer of a sand-based green? A bit of root loss on these greens is the least of my worries considering the high potential for Poaannua encroachment during the cool weather of October and November.
No way is bensulide going to solve all your problems with respect to Poaannua encroachment in new greens, but why not use all the tools in the toolbox available to address this challenge? If well-timed, split applications of bensulide only prevented half of the Poa from germinating in ball marks or aeration holes without causing significant injury to the bentgrass, aren’t making the treatments well worth the modest cost and minimal effort?
Every Poaannua seed that the herbicide barrier prevents from germinating represents one less plant to cull out of the putting surface by hand the next spring…and a penny saved is a penny earned.
Source: Bob Vavrek, firstname.lastname@example.org or 262-797-8743