Poa flower in putting surfaces

Here at Phoenix we have been managing Poa annua on our golf greens ever since they changed to being a high percentage of Poa probably 50 or 60 years ago. The old management techniques have certainly given us some problems underneath in our soils and consequently on top on our surfaces. High kg of Nitrogen per annum, too much water, height of cut too low and lots of disturbance to keep on top of organic matter has started the circle of decline and has given Poa annua the advantage it seeks over other more preferred perennial species like Bents.

There are several sub species of Poa annua, old established push-up greens like here at Phoenix are 95% Poa, but I would have a guess that 90% of that is Poa annua var reptans which is the preferred species. This so called annual actually grows as an annual, a biennial and a short lived perennial. The pure annual species is more prone to death from disease and drought so is definitely not what we want in the green.

All grasses flower and set seed including the desired Bents and Fescues, but on golf course putting greens and bowling greens cut at anything between 2mm and 6mm this will not happen. Poa and it’s ability to flower at low heights of cut is one of the things that makes this grass a prolific propagator. At Phoenix I can roughly tell my percentages of annual type var reptans by the flowering stage and its timing by using Growing Degree Days (GDD). to work out GDD you take the average temperature of the day and subtract a base of 6 degrees.
     
              T(max) + T(min)
GDD =                                  - T(base)
                         2

e.g  23c + 9c / 2 - 6c base = 10 GDD

You start this process on the 1st January and add the GDD together every day. GDD have been used in our industry for a while but different crops, different climates and different situations, for instance Primo (trinexapac-ethyl) applications are timed by the GGD model but with a base of 0. On our golf greens we reapply primo every 200 GGD. The true annual types can flower any time beyond 100 GDD accumulation but the var reptans is usually after at 180 GDD, I have a little GDD counter on my maintenance HUD and this lets me know when to expect the flowering stage. (as of 20th April  160.5 GDD)

Now anyone that has the majority of their putting surface as Bents or Fescues in the UK, the adding up of GGD is a useful tool so you know when not to disturb the surfaces and make a seed bed for this pesky weed by verticutting too deep or hollow coring. In the US they have type 1 or type A plant growth retarders. These can interrupt the plants ability to flower and is a great weapon against the spread of Poa annua, but in the UK we only have type 2 or type B in trinexapac-ethyl and does nothing to stop Poa flower.

So for now we either manage this extraordinary plant or fight it best we can, from experience on a USGA spec or natural sandy free draining rootzone you have a chance of keeping and adding perennial Bents but on a bacterial dominant poor draining clay rootzone your fighting a losing battle and any transition will be expensive and hard fought.