Winter Applications of Plant Growth Regulators Improve Annual Bluegrass Seedhead Suppression
Adam Van Dyke, CPAg, MS, Professional Turfgrass Solutions, LLC
Author email: email@example.com
The use of chemical plant growth regulators (PGRs) in spring is common on golf courses where annual bluegrass (Poa annua) inflorescences (flowers/seedheads) are undesirable. Seedheads negatively impact surface uniformity and playability while lowering turf quality. The plant also uses a lot of energy to produce seedheads – at the expense of leaf and root development during spring. Suppressing annual bluegrass seedheads with PGRs may also improve the turfs ability to tolerate summer stresses.
Mefluidide (Embark® T&O and 2S formulations) and ethephon (Proxy®) have long been the industry standards used to suppress seedheads on golf turf – with a plethora of spring programs involving these products used on the course. Ethephon is primarily used on shorter cut greens, whereas mefluidide is typically used on higher cut tees, fairways, and even roughs. Some superintendents use mefluidide on greens, but although Embark® T&O does not exclude use on greens as does Embark® 2S, the T&O product also does not provide any use instructions for putting greens.
Ethephon products will be the standard seedhead suppressor moving forward because mefluidide is no longer being manufactured. The most common ethephon program for seedhead suppression is Proxy® at 5 fl. oz. per 1000 sq. ft. mixed with Primo Maxx® at 0.125 – 0.25 fl. oz. per 1000 sq. ft. to improve efficacy and safety. A sequential application (or two) is necessary for the best results, with the interval usually ranging from 2 to 4 weeks between applications.
Spring seedhead programs with ethephon (and even mefluidide) can be successful, but those with experience know the effectiveness varies from good to marginal suppression – to outright failure in some years. The variability is mostly from the timing of the first PGR application. The seedhead suppressors don’t work if the inflorescence is fully developed or has already emerged. Many entwined factors of spring weather (vernilization and photoperiod), Poa biotype, and plant growth stage, make the success of seedhead programs unpredictable. The time to begin sprays varies across regions, and is typically initiated by an arbitrary calendar date, a phenological indicator, or degree-day models. Although these methods can increase success, they don’t always work. In northern regions (like Utah) with a distinct winter/spring transition period, typical seedhead applications start in March or April. However, some Poa biotypes have already set seed suggesting inflorescences are initiating earlier – possibly during winter under the snow.
Dr. Shawn Askew at Virginia Tech noticed this phenomenon years ago, and began evaluating late-fall (Sept., Oct., Nov., Dec.) and early-spring (Jan., Feb., March) applications of ethephon to suppress these “rouge” seedheads. What he found was better suppression in spring when these early applications were followed by the typical spring program, compared to just the spring program only. We collaborated to bring this concept to the northern regions, where these applications can be thought of as pre-snow fall and post-snow melt, respectively. Thus, the pre-snow application is “late fall” or “close to snow cover”, and the post-snow application is any opportunity of snow melt in winter (Jan. or Feb.), or after complete melt in March.
Some winter ethephon and mefluidide programs have been evaluated over the past two winters in Utah on annual bluegrass/creeping bentgrass greens with impressive results. Mefluidide treatments were included because at the time it was still available. With mefluidide products being discontinued, programs that utilize Embark® will not be explored further. However, the results are still worthwhile as some of you still have some units of mefluidide that will be used for a few more years. Normal spring timing Proxy+Primo applications were initiated at 350 growing degree days using the base 32 F° model and suppressed 40-50% of seedheads. Not bad, but most would hope for better suppression. Improvements were achieved with winter applications of Embark® formulations (T&O at 10 fl. oz./A; 2S at 1 fl. oz./A) followed by the normal spring Proxy+Primo program that suppressed 60-80% of seedheads. The best suppression has come from winter ethephon applications (Proxy®, Ethephon 2SL®, Oskie®) followed by the normal spring program that has suppressed >90% of seedheads for 8-weeks. The winter applications of ethephon products have been very safe and have not caused crown rising or scalping injury in spring. Surprisingly, turf quality, visual color, and leaf chlorophyll enhancements have also been observed and measured in spring from the winter applications of ethephon, but not from mefluidide. It should be noted that the rates of mefluidide tested in Utah were purposely made at well below label rates due to the potential for more injury from this compound. These rates have been very safe, but again work with mefluidide at the winter timing concept is likely done for now.
Overall, there have not been any “statistical” differences for seedhead suppression between the pre-snow and post-snow applications of ethephon, but the pre-snow timing has been slightly better and more consistent thus far. If you had to choose between one timing I would suggest trying a pre-snow application in November or December in regions with a similar climate to northern Utah (Salt Lake). Suppression is even better if you can make both the pre-snow and post-snow applications before you in initiate your spring program. The post-snow timing should be made at least one month before your typical spring programs begins.
With the success of these winter PGR applications in Utah, there have been questions about possibly combining ethephon at the pre-snow timing with fungicides for snow mold protection on greens – as the timing of these applications usually coincides. There are some treatments on the ground in Salt Lake (4,500 ft. elevation) and Park City (7,000 ft. elevation) to address the safety of such mixtures. Compatibility of ethephon with Instrata® or Interface® did not appear to be a problem, and treatments in Park City will also address any issues with ethephon and frost at higher elevations. Work on fairways with early ethephon timings has also begun in Utah and Virginia this winter. Other safeners (similar to Primo Maxx®), pigments, plant health promoters (such as Signature®, Fiata®, Civitas®, Actigaurd®), and different PGR chemistries (such as Musketeer® and Trimmit®) are also being looked at as tank mix partners with ethephon at these early timings. Our goal is to find tank mixes that improve turf safety and enhance seedhead suppression.
The winter, or early, application concept of seedhead suppressor PGRs is gaining popularity and so far seems to be very positive. Perhaps these early applications can bring flexibility to initiating your spring seedhead program, while at the same time boosting the effectiveness. Give the idea some consideration and we encourage you to experiment at your course as you should see some of the best seedhead suppression you have ever achieved. Keep us updated on your progress.