Lot's of talk about Poa this spring

Winter damage can be a big problem in Poa.

While some golf course superintendents are still seeing the last remaining traces of snow on their turf, most are starting to assess the impact of winter and potential damage. With the predominance of Poa annua as the primary species on many golf courses throughout the region, the potential for winter damage is always high and it appears that the winter of 2010/2011 may be as damaging as that in the summer of "the year that shall not be spoken". According to a recent Northeast Regional update from the USGA's Adam Moeller, it appears that many golf courses have "discovered moderate to severe winter damage on putting greens."

So much of the discussion on Facebook and Twitter has shifted to assessing the damage and fixing it.  In cases where damage was not observed the focus has been on seedhead suppression. The bottom line for those managing turf in the Northeast, the focus surrounds the suppression and/or management of Poa annua.

Regardless of whether you want to manage or suppress Poa, you probably feel pretty strongly about your beliefs!

While this has always been a major interest of mine, the shift to Penn State has given me the opportunity to focus more research efforts on managing this species on golf courses. For those not familiar with our state, Pennsylvania is made up of two major factions: those in the western portion of the state (e.g., Pittsburgh) love their Poa and believe it is the premier species for putting quality while those on the eastern side of the state (e.g., Philadelphia) generally consider this a weed problem and go to great lengths to suppress it (there are always exceptions to the rule, so don't you superintendents in Pittsburgh trying to control Poa yell at me telling me that I am wrong). That leaves me and others at the University trying to figure the best management practices for both those that want to get rid of it and those that want to promote it. And while there are many people that claim to know how to accomplish this, a lot of research-based information is still needed to determine best management practices that meet your specific needs (whatever your needs may be).

So over the next two weeks, I will try to provide some insight into what is generally known about managing/suppressing Poa in our region and provide some insight into research that we have initiated to further assess management options.

Here is a list of what is generally known or believed about Poa management:

Trimmit-treated stand of bent/Poa

PGRs
Primo and Trimmit/Cutless are the three most common growth regulators applied to turf during the season. Primo is believed to have little impact on Poa (other than making it stronger), while Trimmit and Cutless have been show to favor the growth of bentgrass over annual bluegrass when used a repeated application program.

Herbicides
There has been no silver bullet herbicide for managing annual bluegrass. Preemergent herbicides effective against Poa are generally not recommended for use on putting green turf. Postemergent herbicides such as Prograss and Velocity have been used with varying results, but again are not labeled for use on putting greens. Various experimental products (cumyluron, methiozolin, others) are currently being evaluated in the United States and have shown great promise. For example, methiozolin is currently labeled for putting green turf in Korea and has excellent efficacy in preliminary studies, but more studies looking at the use of this product are needed.

Coring can create an ideal Poa seedbed

Cultural practices
This is where we get into the relatively ongoing controversy of management programs. In recent years, there has been a resurgence of programs that involve minimal disturbance (no hollow tine aerification or deep vertical mowing), low nitrogen and phosphorous programs, high ferrous sulfate (and other sulfates) applications, and others. Unfortunately, many of these recommendations are based on "theory" and have not be thoroughly evaluated in controlled research environments.

The general feeling regarding cultural practices for suppressing Poa as I understand it are:

1. Low nitrogen will favor the bentgrass over the annual bluegrass and in turn result in less accumulation of organic matter. ADDED CONTENT: (Low P will also favor bent...thanks Dr. Koski for pointing this out)
2. Ammonium sulfate as a primary N source will result in acidification and therefore further favor bentgrass.
3. Fe, Mg, and Mn sulfate will help in an acidification of the foliage (not sure where this came from) and therefore favor bentgrass AND help to offset color deficiencies in low N programs.
4. Core aerification surrounding times when annual bluegrass germination is optimal should in general be avoided. Many of these new Poa management programs dictate that greens be vented often, but that any disruption should be avoided.
5. To further help dilute the potential build-up of organic matter, frequent topdressing is generally recommended to encourage the development of a manageable "mat" layer rather than a puffy "thatch" layer.
6. I have no idea where this fits into the program, but many seeking to reduce Poa populations are lowering their mowing heights. This seems counter intuitive to me, but that's what I'm seeing and hearing.
7. As would be expected, irrigation is minimized to further stress the Poa and favor bent. In this entire program, this one seems like a no-brainer to me and the diligent and thrifty use of water is in general a good idea for limiting Poa as well as associated turf diseases.
8. There are probably other things that I have left out, but this post is already getting too long...add your "#8" in the comments or on Facebook.

So now you have a general overview of some of the techniques that superintendents and greenkeepers are using around the United States and around the world. Please feel free to add to the comments any additional positive or negatives you see with these management practices. Some of them are controversial to say the least and I have seen people swear by all or a selection of these practices to help "favor the strong species while eliminating the weak" and I have seen others who after several years on the program(s) lose a significant amount of turf.

Next week, I will share some preliminary results of our modified version of the program above which investigates the interaction of nitrogen rates, ferrous sulfate rates, and plant growth regulators on Poa annua populations.