2/29/2024 - By Dr. Paul Giordano

Anyone who manages populations of annual bluegrass (Poa annua) knows that spring/summer seedhead production is one of the biggest issues for playability on putting surfaces. Over the years, products like ethephon (Proxy®) and mefluidide (Embark®) have been used with varying degrees of success to limit the production of seedheads. With mefluidide gone for several years now, the industry’s only true option is ethephon – which happens to be less effective and less consistent than mefluidide in achieving high levels (>90%) of seedhead control.

Much research has gone into improving the efficacy and consistency of ethephon over the years. Below, are some tips and tricks based more recent work done that should help with seedhead struggles. 

Spring Applications

As we move into spring, early season applications for seedhead control are critical in achieving consistent results. Traditionally, two spring applications of Proxy after green-up have been used as a standard for controlling Poa seedheads. However, this strategy has proven to be somewhat inconsistent based on geographic region and annual bluegrass biotypes. Growing degree day models have helped to schedule applications and improve consistency of suppression, especially the initial spring application of Proxy. More recently, research has indicated that annual bluegrass may initiate seedhead production in late fall or early winter – well ahead of visible emergence in the spring. This has led to recommendations and adoption of Proxy applications starting in the fall or winter to improve upon overall seedhead suppression and consistency. 

Regardless of whether you made fall/winter application or not, you should start spring Proxy applications around 200 GDD₃₂ or 50 GDD_50.  A rule of thumb is it’s always best to apply the first spring application on the early side rather than too late. From there, follow up applications should occur on 3-4 week intervals or every 200-400 GDD₃₂ / 50 GDD₅₀. This strategy has been proven effective after many years of practical experience from golf course superintendents across the country. Rates and application frequency can vary based on seasonal length of seedhead production and Poa annua biotypes on a particular site. 

A Note on GDD Tracking

Many different websites can be used to get a reasonably accurate measurement of growing degree day accumulation for your general area. GDDTracker from MSU is a popular site that includes a Proxy/seedhead model. Syngenta also offers a free GDD tracking tool on their GreenCast.com website. Several other websites and applications are available for this purpose as well. Regardless of the site or app you use, it’s important to understand the date at which the tracking of GDD accumulation begins.

Some sites will “reset” on January 1^st and GDD accumulation begins at the start of the new year. Others, like MSU GDDTracker, don’t begin counting until February 15^th. This is particularly important to understand in “abnormal” years where exceptionally warm conditions persist in January and February - If using a site that begins in mid-February, you’ve likely underrepresented actual GDD accumulation for your area. 

Fall and spring Proxy® recommendations for controlling annual bluegrass seedheads (Bayer).

Always read and follow label instructions and guidelines.

Reach Out to Your Harrell’s Rep

Take control of your Pao Annua seedheads today, contact your Harrell’s representative for help in diagnosis, product recommendations/programs, or any other questions you may have.