Fall Proxy applications for Poa annua seedheads

Clark Throssell, Ph.D., interviews Zac Reicher, Ph.D., a technical specialist on the Green Solutions Team with Bayer Environmental Science. He has more than 30 years of turfgrass research experience and has conducted many annual bluegrass control experiments on research plots and golf courses. You may reach Zac at zac.reicher@bayer.com for more information.

Clark Throssell

Q: Describe annual bluegrass seedhead initiation, biotypes and reasonable seedhead control expectations.

Annual bluegrass (Poa annua L.) seedhead initiation occurs in most locations during the shorter days of late fall and winter. That said, there are many biotypes of annual bluegrass, and their behavior varies tremendously across the country. In some locations where annual bluegrass stays green all year, seedhead production may occur year-round.

Seedhead control of 70 percent to 85 percent is a reasonable expectation when using Proxy (ethephon, Bayer). Some superintendents report a few seedheads still visible after a Proxy program, but they usually are low in the canopy and do not affect playability.

Q: What are your thoughts on fall applications of Proxy to control annual bluegrass seedheads?

First, if you are pleased with your current annual bluegrass seedhead control program, stick with it. If you are seeking better results with Proxy, we have seen improved seedhead control and better consistency of control by adding a late fall application in addition to the typical spring applications.

Q: What is the recommended timing of fall Proxy applications?

In locations where annual bluegrass goes dormant, make the fall Proxy application when the shoot growth of annual bluegrass slows dramatically, or apply Proxy in a tank mix with snow-mold-control fungicides.

In locations where annual bluegrass does not go dormant, make the fall Proxy application when the growth of annual bluegrass slows in November or December.

Q: What is the recommended timing of spring Proxy applications if a fall Proxy application has been applied?

In locations where annual bluegrass goes dormant, make the first spring Proxy application at 150 to 200 growing degree days (GDD) base 32 degrees F starting GDD accumulation Jan. 1. This model works well for northern and Midwest locations. In Mid-Atlantic and Northeast locations, apply at 50 GDD base 50 degrees F starting GDD accumulation on Feb. 1.

Though the fall Proxy application adds more flexibility in the timing of the first spring application, it’s always better to make the first spring application earlier rather than later.

Make the second spring Proxy application after 200 GDD base 32 degrees F or 50 GDD base 50 degrees F has accumulated since the first (prior) Proxy application (typically three to four weeks later). We recommend Primo Maxx (trinexapac-ethyl, Syngenta) in the second application for improved growth regulation and turf safety. Two applications of Proxy normally are made in the spring, but three or more applications may be needed in areas with extended seedhead production periods.

In locations like the Transition Zone or the Pacific Northwest, where annual bluegrass does not go dormant, make the first spring Proxy application at 50 GDD base 50 degrees F accumulation starting Jan. 1. Make additional Proxy applications on a three- to four-week interval as long as seedheads are produced, or use the 50-GDD-base-50-degrees-F accumulation since the last Proxy application during springs that have widely varying temperatures.

Q: Are there concerns about winter damage following Proxy applications in fall?

There have been thousands of fall Proxy applications to putting greens, and we have not been able to correlate Proxy applications with winter injury.

Always leave an untreated check by covering the turf with a 4-by-4-foot piece of carpet or plywood on the back of several greens to see if the fall Proxy application is affecting seedheads, spring green-up or winter performance.

Q: Is there anything else you would like to add?

Some superintendents may be hesitant to try a fall application of Proxy on their greens. In these cases, I recommend adding Proxy to the spray tank for the last two or three greens or on a practice putting green when treating for snow mold.

Clark Throssell, Ph.D., loves to talk turf. Contact him at clarkthrossell@bresnan.net.