As creeping bentgrass greens age, one of the greatest challenges is limiting the amount of Poa annua contamination that inevitably develops and becomes more problematic over time. Its persistence is nothing short of incredible, and control requires a good understanding of plant physiology, herbicide sensitivity and the timing of various cultural practices. So, here are a few things to keep in mind if you want to “slow the Po” in bentgrass greens.
- Careful timing of cultural practices such as hollow-tine aeration with large-diameter tines (i.e., >0.375 inches) can reduce the amount of Poa annua contamination. Typically, targeting late summer instead of early fall is a good idea when trying to promote creeping bentgrass over Poa annua. Most Poa annua will germinate when soil temperatures at a 2-inch depth cool to 66 F or less for several consecutive days and adequate moisture is present.
- More surface disruption typically results in greater Poa annua pressure. It is an incredibly opportunistic plant and when voids are created in the turf canopy, Poa annua is happy to fill in. With that said, withholding cultivation for the sole purpose of reducing Poa annua pressure is not desirable if the result is excessive organic matter accumulation. You must find a balance, and organic matter management takes higher priority.
- The use of Class B plant growth regulators (PGRs) has been widely accepted and successfully implemented to reduce Poa annua populations over time. These PGRs slow the growth of Poa annua more than creeping bentgrass, which places the competitive advantage in favor of bentgrass.
- Ultimately, creeping bentgrass has two major weaknesses – shade and traffic. Reducing these when possible can help give bentgrass an edge over Poa annua. Where bentgrass struggles under shade and traffic, Poa annua is ready to thrive.
- There is some relatively new chemistry available to help selectively control Poa annua in bentgrass greens. While it has worked well thus far, it is important to implement a comprehensive management program to discourage Poa annua and create an environment that is favorable for bentgrass to ensure long-term success. Poa annua has developed herbicide resistance to many other chemistries and it is wise to implement sound practices to help delay potential resistance to new products as they become available.
Effectively slowing Poa annua contamination into bentgrass greens requires a comprehensive strategy. If there was a silver bullet, very few courses would continue struggling with this incredibly opportunistic species. If you would like help developing Poa annua management strategies in more detail, contact your regional USGA agronomist.
Central Region Agronomists:
Zach Nicoludis, regional director – znicoludis@usga.org
Paul Jacobs, agronomist – pjacobs@usga.org
Information on the USGA’s Course Consulting Service
Contact the Green Section Staff