Bermudagrass encroachment

“Why are there dead spots on the green?”

Now is the time of year when the weather is mild, the rough is dormant, the fairways are lush and the greens are great.  Well, almost great…

What I mean by almost great are the off color spots that seem to pop up on the bentgrass greens that “appear” to be dead. First I want to use correct turf speak and say “dormant, not dead”. Anyway, these spots are dormant bermudagrass.  Some of the questions posed about these areas have been: What is it? How did it get here? And why can’t we get rid of it? In this article I will attempt to answer these questions. 

First, what they are. The spots in the greens are, as mentioned, bermudagrass. These spots exist throughout the season.  However they become more prevalent in the winter months. Bermudagrass becomes dormant in the winter months. Dormancy causes the plants to lose their color. The undesirable brown color stands out in comparison to the bentgrass which still maintains full color.

How did the bermudagrass get into the center of the green? This is a question that has many answers. There isn’t one particular reason as to why or how it got there. There are combinations of circumstances that lead to bermudagrass encroachment. The weakening of the bentgrass stand in the summer affords the proper environment for bermudagrass propagation. It is in these weak spots that the bermudagrass will ultimately appear and take over. Once a proper ‘seedbed’ is in place, all it takes is a few seedlings and/or sprigs and the establishment process has begun.

There are many ways that seedlings and sprigs can get into these weakened areas. Wind, animals, and maintenance equipment are all carriers for the seeds/sprigs. But two of the largest contributors to seed/sprig transportation are the aerification process and foot traffic. During aerification there are a lot of operations that can lead to bermudagrass movement. The opening of holes in these weakened areas enhances the chance of bermudagrass survival. The subsequent pushing, dragging, and blowing of cores aids in movement from the edges to the center of the greens and ultimately into these weakened areas. We have altered our aerification process to minimize the amount of bermudagrass movement from the edges. The use of a circular aerification pattern and cautious core removal has reduced the movement of bermudagrass sprigs onto the putting surface. We will continue to stay on the cutting edge of technology to lessen the bermudagrass contamination during aerification. Aside from aerification, foot traffic is the other major culprit in spreading seed heads.

Everyone that’s cleaned golf shoes knows how many seed heads can become entrapped in the spikes. It is these seed heads that are picked up from the tees, fairways and rough and then transplanted onto the greens. David Pelz wrote in his book “The Putting Bible”, that the average foursome takes 500 steps on each green. Multiply this by fifty groups and you have 25,000 steps per day on each green. Each step presumably contains at least one seed head and or sprig. It is in these seed heads and sprigs that the bermudagrass patches can begin.

Well now that we know what they are and how they got there, the question remains… how can we get rid of it?

There are a couple of ‘suggested’ ways to rid and control the bermudagrass encroachment problem. The first and most effective way is physical removal. The second is with the use of select chemicals to stunt the bermudagrass. Both methods are effective in their own right but neither completely rid the turf of contamination.

I know it seems hard to believe that physical removal wouldn’t be 100% effective, but it isn’t. In fall of 2008 at the Players Club, we put together a project to remove all of the bermudagrass on the greens surface (excluding the perimeter encroachment). We extracted over 2,000 square feet of sod and installed clean A-1 bentgrass. At completion we were confident that we had solved the problem. It wasn’t until winter 2009 that we realized just how much bermudagrass remained.

In the picture to the left (taken 1/11/12), you can clearly see the dormant bermudagrass. You can see a small area of green grass in the center of the stand. This green turf is bentgrass. In particular, it is the bentgrass that we installed in 2008. What transpired over the past two years is clear. During removal we were unable to identify the true quantity of bermudagrass beneath the bentgrass surface. This allowed a good portion of the bermudagrass to remain, only to emerge in the spring. The remaining bermudagrass then continued its dominance of the L-93 bentgrass in an outward pattern. Interestingly enough, the denser, more heat tolerant A-1 bentgrass continues to fend off the bermudagrass invasion.

            The second approach to encroachment control is the use of a selective herbicide. The mode of action is to stunt the growth of the bermudagrass. The timing of the applications is the key to any success associated with this method. We apply our herbicide once in the late fall and 2-3 times in the spring annually. The idea is to attack the bermudagrass as it enters dormancy and again when it emerges in the spring. The goal is to suppress the bermudagrass enough to allow the bentgrass to reclaim the void on the greens surface. 

While this product does a fair job in suppressing the bermudagrass, the problem arises in the summer as the bentgrass weakens. The progress achieved in the fall and spring can be completely nullified by an unforgiving summer.  And as we can all attest the past few summers have been rather unforgiving. Overall this method provides moderate improvement in the spring and fall, however to maintain any type of sustained success it is imperative to have Mother Nature’s support.

             With that said, we will continue to manage this problem with the most cost effective solutions available. Be it physical or chemical we will continue the search for solutions to this common problem affecting bentgrass greens in the South.