Bentgrass vs. Poa annua

We have started using another new growth regulator this summer in an effort to promote the spread of the bentgrass on our putting surfaces as well as help keep the Poa annua on its heels.  This product regulates the Poa much stronger than it does the bentgrass, giving our desired species a more competitive advantage.  We have been starting with relatively light rates, but even with those the Poa has started to turn yellow and shows a sunken appearance in the turf canopy.  It has slowed the growth of the bentgrass, but not so much that it doesn't continue to prosper and slowly start to spread and take over the Poa plants.  

The pale yellow dots are all Poa annua plants that are being regulated
to the point where they start to decline, leaving the bentgrass to slowly
take them over.

This is a fairly painless process on most of our greens that contain only about 20%-30% Poa annua.  Combined with a few other management practices that favor the bentgrass over the Poa (reduced watering, less fertilizer, use of acidifying fertilizers, etc) and I feel like we should be able to get the Poa populations down to 5%-10% on these greens in the coming years.

However, a few greens in particular (1, 2, 6, and 10) have a significant amount more Poa in them than the rest, more in the range of 50%-80%.  These greens are going to be a struggle to make an effective and rapid change over to a more pure bentgrass stand.  We will likely have to continue using the lower rates of Trimmit on these greens, as increasing the rate more than we are using it already may lead to complete death of the Poa and thinning on the putting surfaces.  We will also continue to interseed the green with bentgrass seed a few times a year to help boost the population.

10 green shows that all of the light green area is Poa annua, while the
bentgrass is the smaller, bluish green patches.

The real struggle in this process however is with the collars that surround the greens.  For whatever reason, most of the collars are in the 90%-100% Poa population range.  I don't see any effective way to convert a stand that contains no bentgrass over to bentgrass, so I really think the only logical solution around the edges of the greens is to continue sodding out the dead Poa every spring, and maybe even sodding out some living Poa whenever we have the chance.

This picture of the edge of 5 greens sums it up perfect.
There is an unnaturally perfect line seperating the two
species between the bentgrass in the green, and Poa
in the collar

The big question of course is why fight the Poa when there is so much of it there?  First and foremost, the Poa annua will die here in 9 winters out of 10.  Trying to keep it alive is a futile effort that almost always leads to disappointment, headache, and horrible golf conditions for us in the spring.  Secondly, the Poa is generally a weaker plant, meaning that it requires more fertilizer, water, and pesticides to keep it alive all summer.  Our cost of inputs to keep the greens healthy throughout the summer could drop by at least 50% if we didn't have to try to keep the Poa alive.

Here are a few reminders from the last few springs as to why we want more bentgrass on our golf course and less Poa annua.

17 green, alive, bentgrass.  Collar, 90% dead, 90% Poa

3 green, Poa all dead, strip of bentgrass sod, completely alive.

17 collar, Poa all dead, strip of bentgrass sod completely alive.

Lastly, here is a picture from 6 green this spring.  That green is almost entirely Poa, and showed the effects of that early on.  Stay tuned for a blog post next week about some upcoming plans for 6 green.