Wednesday, April 25, 2012

Bentgrass vs. Poa: There is a difference!

Each year golf course superintendents in the northern United States wage a war between bentgrass (Agrostis stolonifera) and annual bluegrass (Poa annua).   Regardless how little or how much of each you have, a concerted effort is made to minimize Poa annua.  Poa annua is a weed and can cause a lot of headaches for golf course superintendents and members alike!  At Ridgeway Country Club we have about 80% Poa to 20% bentgrass putting surfaces. Here are the reasons for minimizing Poa annua on golf courses:
1.       Winterkill:  Poa annua is susceptible to all kinds of winterkill. Types of winterkill include: prolonged periods of ice, crown hydration, desiccation, snow mold, and direct temperature kill. Bentgrasses are far less susceptible to winterkill than Poa.  Because bentgrass is less susceptible to winterkill this is why one golf course’s greens succumb to winterkill and the course across the street does not.  If you have bentgrass, your chances of winterkill are much, much lower.  
2.       Heat stress:  Poa does not perform well under warm/hot conditions.  Heavy rainfall and humidity make the problem worse.  This is particularly a problem on greens that do not have adequate surface and subsurface drainage.  Also heavily shaded greens are more susceptible to massive turf loss during warm conditions (#13 green at Ridgeway).   Bentgrass is at its competitive advantage in summer when it thrives better than does Poa.
3.       Seed heads:  Poa has a competitive advantage over bentgrass because it is a prolific seeder.  This allows for the regeneration of Poa once it dies.  This comes at a cost in playability in the spring when the plant seed heads cause the greens to be very bumpy.  Proper chemical controls on greens are needed to prevent this to provide adequate putting quality.   Bentgrass does not seed out in fine turf areas hence it does not cause problems in playability with seed heads.  
4.       Pesticides:  Poa is a grass that requires a lot of pesticides because of the amount of diseases and insects that can cause damage to the plant.  This is particularly true during times of summer heat and stress.  Bentgrass is much better in this regard, requiring less pesticide input.
5.       Fertility:  Poa is much more reliant on fertilizer than bentgrass.  This again makes Poa a more unsustainable grass when compared to bentgrasses.
6.       Water:  Poa is a weed and a weak rooted plant.  It requires ample water to stay alive.  Good bentgrass surfaces require much less water and provide a much more sustainable playing surface.
7.       Color: Poa has a lime green color as opposed to a rich darker blue-green color of bentgrass.
8.       Consistency:  With all of the problems above, consistency with greens that are largely Poa is a problem.  When we have drier moderate temperatures Poa greens seem great, then with heat and rain they make for a very poor surface.  Our greens are a perfect example of this scenario.  When the weather is good our greens are great, when we get winterkill, summer stress from heavy rain and heat our greens are not as good.  These two scenarios call for a BIG variance in playability.  Bentgrass tends to have more consistency because it is not affected as much by all of the factors mentioned above.  Keep in mind weather is not the only factor at play.  Drainage both surface and subsurface plays an important role in evacuating water as efficiently as possible.  Shade prevents turfgrass plants from photosynthesizing effectively thus plants are not able to store carbohydrate reserves.  Plants overall are weaker and susceptible to diseases, turf thinning, slow recovery, winter and summer stress.
As you can see there are a lot of reasons to dislike Poa and it really presents some interesting challenges for both superintendent and golfer.  So far this spring the greens have been very nice however let’s not forget last year’s winterkill and some of the summer problems we have experienced on these Poa greens.
The Ridgeway maintenance staff is committed to providing for the LONG TERM health of Ridgeway and its playing surfaces.  We are committed to improving both surface and subsurface drainage on the golf course.  We are also committed to making the proper tree removals to improve turf health quality and playability. 
Lastly we are committed to turning the tide from Poa to bentgrass.  We will do so by favoring what bentgrass thrives in, which is turf that is not reliant on overwatering, over fertilization, and the excess use of pesticides.  The combination of sun, surface drainage, subsurface drainage, chemical practices and cultural practices will allow us to increase our bentgrass population.  Once we have a predominate stand of bentgrass we will no longer be held hostage by events that are out of our control like the weather.  Keep in mind this process is slow and many pieces will have to take place to make it happen, which is why projects like XGD drainage and greens re contouring are important pieces of the puzzle.   Once the greens are bentgrass we will be able to maintain, instead of keep alive . . . at that point we will have won the battle of bentgrass vs. Poa.

Bentgrass is the purplish green.
Poa is the lime green.
This stand is predominatly bentgrass.
Taken from #2 green.

Bentgrass is the purplish green
Poa is the lime green.
This stand is predominatly Poa.
Taken from #2 green.