Poa Annua, Taking Over?

Poa annua is the number one talked about grass in America. Courses throughout the country experience Poa invasion at all levels. The Northwest golf courses are nearly all 100% Poa annua including greens. We are currently looking at about 30% contamination on the golf course and less than 1% contamination on the greens.

Poa has been slowly invading the golf course since the construction. Poa is a very efficient annual grass plant. A prolific seeding capability has generated a substantial seed bank over the years since construction. The turf was compromised by disease three and four years ago giving the Poa a great opportunity to germinate with less competition. This has in turn given us enough of a population to become more noticeable each season.

We have used Trimmit, a plant growth regulator that regulates the Poa plant enough to give a slight advantage to the host turf, the idea being to potentially out compete the vulnerable Poa. We have tried increasing rates of this product, but have only succeeded in making an uneven playing surface in the spring from the patches of Poa being sunken into the surrounding turf. I have not seen the expected regression on the larger patches of Poa. Now, on the greens we are nearly 100% clean. I would have to say Trimmit has some impact on the smaller patches within the creeping bentgrass. We also use hand picking for the small plants in the spring. Trimmit has done a great job on the pinky sized plants on the greens and we have been successful in keeping the bentgrass clean.

The question becomes, what do we do or what can we do now? My opinion on this subject is more of a realistic approach rather than my normal optimistic approach. Depending on how aggressive our membership would like to tackle this issue, we will have continual spread of the Poa. Using chemical control becomes very expensive and results in less than satisfactory results when it comes to complete eradication of the Poa. We can try to manage seed head production in the spring to not get the puffy broccoli looking turf, but we would be kidding ourselves if we thought that we were making a dent in the Poa seed bank that has accumulated over the years. This would be a purely aesthetic approach for a great deal of money. Growing up in the Poa capital (Pacific North West) and working on relatively new courses I have seen every kind of control exhausted on Poa and I have yet to see one successful in complete eradication. Some have wiped out a lot of grass, but then you are stuck with trying to beat the Poa from germinating and filling in the spots left from the old dead Poa. It is a very difficult task.

Folklore surrounding Poa is that it will die in the summer heat. This is a common misconception. There is no doubt Poa is a little less drought tolerant than other grasses due to the smaller root structure, but in our climate Poa will not die unless something out of the ordinary happens. There is no doubt Poa has a smaller root system then it's competition but it is a pretty resilient plant, it has started to take over in a pretty difficult growing media and is good at out competing the resident turf. Poa isn't as weak or quick to expire as some of the folklore explains. (Joe Vargas, Proffesor MSU)

What I can say is, Poa control is very expensive and will only prolong the inevitable. Spending valuable resources on Poa may not be the best answer at this time. If you are not getting complete (100%) control on seed head production or simple eradication, Poa will always prevail. Being a logical thinker, I look at the hundreds of thousands if not millions of poa plants growing on the course, if I spend valuable resources to get 80% or even 90% control then we still realize that we have hundreds of thousands of plants still producing millions of seeds that season.

The seed head production will subside later in the spring and the playing surface is not bad at all. Pebble Beach and Cypress Point are both 100% Poa tee to green. I grew up playing and putting on Poa surfaces and the lie you get on a patch of Poa is like placing the ball on a tee. The greens on the other hand we will make adequate efforts to ensure that they stay as clean as possible since Poa patches on putting greens make putting bumpy and inconsistent.

Discussion will continue about Poa. It comes down to playability and presentation, which is more important, how aggressive do we want to get, and do we feel that some type of control is necessary? This issue will become increasingly more noticeable as the years continue...