Evaluations of Proxy/Primo tank mixes, timing, and rates for Poa annua seedhead suppression - 2004 Results April 13, 2005 Effects of Proxy/Primo combination on the collar. Untreated area is above the line vs. the treated area below. We have completed our fourth year of testing products for springtime suppression of seedhead formation by Poa annua. For an overview of the topic and previous results, see our articles published in the USGA Green Section Record and USGA Turfgrass and Environmental Research Online. In past studies, we have confirmed some seedhead suppression with wetting agents (such as Aqua-Gro L), while the PGRs mefluidide (Embark) and ethephon (Proxy) have often given high levels of seedhead suppression. However, Embark treatments may result in unwanted phytotoxicity of greens-height turf, so recent studies have focused on Proxy, alone and in tank mixes with trinexepac-ethyl (Primo). In 2004, we looked primarily at timing and rates of Proxy (ethephon) + Primo Maxx tank mixes on putting green-height turf, including a reduced 3 oz./1,000 sq. ft. rate of Proxy. Tests took place at Aurora C.C. (thanks to John Gurke, CGCS and Keith Krause for their assistance) under intensive putting green management conditions. In fact, the site in '04 was the no. 2 green at ACC, which was under normal playing conditions during the study. The green consists of 50-60% Poa annua, with the remaining turf comprised of various types of creeping bentgrass. Mowing height for this green was approximately 0.12" during the study, and it received standard fertilization and irrigation. Test applications were made beginning April 5 or April 15, with follow-up applications on a two- to four-week schedule (see Table 1). We noted the first seedheads on the site on the April 20 rating day. Application rates, timing and results are presented in Table 1. Poa annua seedhead production was rated visually as percent of Poa plants with visible flowering, not percent of total plot area with visible flowering. Since the green was mowed daily, seedheads were constantly being removed, which limited the total percentage of seedheads visible at any one rating date. Peak seedhead production at Aurora C.C. occurred around May 27, then lingered through most of June (see results table below). Treatments with Proxy + Primo tank mixes resulted in 80%-plus seedhead suppression when compared to untreated controls, most notably during the May 18 to June 9 rating period, when check plots were seeding more heavily. There were no strongly significant differences among application rates or different timing of applications in this study. However, some evidence materialized that the early, low-rate Proxy treatment (treatment #2 in Table 1) was starting to fade by June 9, compared to the higher (5 + 1/8) rate applications made on April 15 and May 18 (treatment #9). A probable protocol for Proxy + Primo Maxx tank mixes on greens-height turf will be the lower 3 oz. + 1/8 oz. application rates applied on a three-week interval (treatments #2 - 5). Please note: depending on application rates, timing and biotypes of Poa annua present on your course, YOUR RESULTS MAY VARY! Thanks to our cooperators and supporters for these studies: John Gurke, Supt., Aurora CC Jim McNair, Supt., Orchard Valley GC USGA Green Section - Regional Grants - Paul Vermeulen, Director, Mid-Continent Region Bayer Crop Sciences - John Smith, Senior Product Development Specialist For more information, e-mail newsletter@interactiveturf.com.