Poa annua management strategies (Part 2)

Last week I introduced the topic of annual bluegrass management practices that are gaining momentum in the United States and other parts of the world. While these practices have been met with some controversy, they have also made us as researchers spend a little more time investigating the implications of these practices for golf course superintendents.

One program that has emerged among many superintendents (many with a strong voice on twitter including @nccturf, @MinikahdaTurf, among others) is the incorporation of various management techniques that seek to favor the bentgrass over the weaker Poa annua spp. While there is much variation in the programs and none are identically alike, a general overview of some of the practices incorporated into the program were discussed in last week's post.

As I also mentioned in last week's post, those of you managing Poa (regardless of your management goals) usually have a very vocal and firm belief of why your program(s) works. As an academic, I try not to jump on anecdotal claims, but do like that they can serve as a catalyst that drives research. For me, it's about trying to figure what works and what doesn't (again based on research) and then trying to fine tune those results into programs that are repeatable across a variety of regions and under different management and environmental situations. So, in 2010 we initiated several studies looking at the management and suppression of Poa under golf course putting green conditions.

Kyung Han assessing Poa populations

Four studies were initiated investigating the interactions between and among the following variables: 1) low and normal/high seasonal nitrogen rates (low and high are about 0.5 and 2.2-3.0 lbs N/1000 sq ft/year); 2) plant growth regulators (none, Primo, and Cutless); and 3) Ferrous sulfate rates (0.0, 0.25, and 1.0 lb/1000 sq ft every 3 weeks).  There are a lot more details to the trials, but since this is only the first year and we have another full year of the study (and hopefully several years more, funding pending) I will save the details for the publication. Other common factors in the study include: routine topdressing, no disturbance, routine venting with solid tines, minimum irrigation where possible, no phosphorous applications, pesticides only where needed, and probably others that I am forgetting. The studies were setup as a 2x3 or 2x3x3 factorial with four replications.

Trials were initiated on a research putting green at the Joseph Valentine Turfgrass Research Center to investigate the interaction of N rates, PGRs, and Fe rates on annual bluegrass populations on a putting green.

So as not to bore everyone with a ton of data, I have included one slide showing results of the 3-way factorial study which included all factors. Data shown is only a single date and it should be pointed out that tremendous seasonal variation in Poa annua was observed between summer and fall timings. Total Poa was estimated at 20 to 25% throughout the area at the beginning of the study and here are the results after the first 5-6 months of initiating the first treatments.

Poa annua populations following the seasonal application of various N rates, Fe rates, and PGRs. Data were collected monthly, but peak annual bluegrass ratings taken in October 2010 are shown here.

Now there is a lot of data to be analyzed and interpretation will definitely be reserved for AFTER we have two full years of data, but here are the general summaries that I have based on this first year:

1. Nitrogen rate (0.5 vs. 2.2 lbs N/year) appeared to have an slight impact on Poa annua populations with lower N resulting in lower % Poa in October.
2. PGRs had the greatest impact with Cutless treated plots (as expected) reducing Poa the greatest. Interestingly, the Primo-treated plots appeared to reduce populations when comparing low to high N plots, but these data need to be subjected to contrasts which have not yet been done to determine the significance of this effect.
3. Ferrous sulfate so far does not appear to have any impact on the Poa annua populations. Many utilizing this program are suggesting that these applications are important to reducing Poa, but based on this first year data it does not seem to have much impact. Having said this, the turf color/quality in plots receiving low N levels started to decline and in plots where Fe was applied it did appear to help improve the overall color...although quality was still a little suspect.

So, this is the first look into the data that we have from the first year of our Poa management study. There are probably a lot of questions about some of the details of the study, but I am leaving that for another time as I hope to continue this work for several years.

The main questions that I have regarding the long term impact of this study will be the assessment of organic matter buildup, changes to the pH (of which we have seen none yet), and the development of side problems such as black layer due to the sulfates. I have also been told that this program will result in a substantial reduction in disease severity and therefore a reduction in the overall use of pesticides. These will all be things that we look at as the study progresses this year and beyond. In addition to these studies, we will be looking at more chemical-based means of suppressing the weed as well...we can't rely on just one method and most likely it will take a combination of chemicals (or "poisons" as our friend "Poa annua" on facebook calls them) and sound management practices to get Poa populations where you want them.

Acknowledgements

As many of you know, funding for these research projects can be expensive. This research could not be possible without the support of The Penn State College of Agriculture and Department of Crop and Soil Sciences, The Center for Turfgrass Science, The Pennsylvania Turfgrass Council, SePro, and the USGA.