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Evaluation of Proxy as a Poa Seedhead Inhibitor

Summary: Following up on 1999 trials that demonstrated the efficacy of ethephon (Proxy) as a Poa annua seedhead inhibitor, six replicated field trials were conducted at four different golf course locations during 2000.  Both cool season putting greens and overseeded fairways served as test sites for the continued evaluations of the seedhead inhibitory effect of ethephon, and ethephon combinations with trinexepac-ethyl (Primo).  Key results include:

  • The use of Proxy at rates of either 5 oz or 10 oz/1000 square feet resulted in a significant decrease in the density of Poa annua seedheads.  This effect was observed for as long as seven weeks after a single application of Proxy.
  • A single application of Proxy at 5 oz/1000 sq ft resulted in significant suppression (45-85%) of poa seedheads on golf course greens and fairways.
  • There was a lag time of approximately 3 weeks before significant seedhead suppression was observed .
  • Suppression with the 5 oz rate of Proxy declined to <50% by 7 weeks after treatment
  • The level of seedhead suppression was positively correlated with rate, with the 3 oz rate of Proxy resulting lower suppression (10 – 55%) and the highest rate (10 oz/1000 sq ft) resulting in the highest levels of suppression (up to 97%)
  • The addition of Primo (>0.060 oz/1000 sq ft) to Proxy (5 oz/1000 sq ft) resulted in a significant increase in seedhead suppression, as well as improved turf quality on golf course greens
  • When used by itself, Primo had little or no effect on seedhead suppression
  • Embark (mefluidide) provided very good poa seedhead suppression, and is the standard product currently used for this purpose on all poa greens (Table 3). However, the product had to be applied every 3 weeks, and significant (though reversible) turf discoloration resulted.  This product causes signficant damage to bentgrass and is therefore not utilized on greens containing bentgrass.
  • Timing Proxy applications to target early seedhead formation (January/February in coastal and inland Southern California) appears to result in better seedhead suppression than applications made later in the season (March/April). The higher temperatures characteristic of the Low Desert may require an even earlier application initiation. Developing optimal timing strategies require further work.
  • Proxy caused no discoloration or phytotoxicity on any of the turf types tested including Poa annua, bentgrass, perennial ryegrass and bermudagrass.
Printable version of full report Principal Investigators: Wendy Gelernter, Ph.D. and Larry J. Stowell, Ph.D., CPPP, CPAg Cooperators:  Gary Dalton, San Diego Country Club; Nancy Dickens, Mountain Vista Golf Course; John Harkness, Oak Valley Golf Course; David Major, Del Mar Country Club Sponsors:  Chris Olsen, Aventis; PACE Turfgrass Research Institute
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