PACE Turf - Turfgrass Information Center

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

Efficacy of sulfonylurea herbicides for improved transition on bermudagrass fairways

Summary: A replicated small plot study was conducted on ryegrass overseeded bermudagrass fairways to evaluate the ability of several herbicide products to remove overseeded perennial ryegrass and thus improve the quality of the underlying bermudagrass base.  Based on the results, the following conclusions were drawn:

  • All treatments produced significantly accelerated increases in bermudagrass cover vs. the untreated check.  The greatest increases were seen with Revolver (0.2 oz/1000 sq ft), applied early in the season (5/7/03). 
  • All treatments produced relatively rapid (within 1-3 weeks) death of perennial ryegrass and Poa annua.
  • All treatments produced some yellowing of turf or in some cases some bare spots, due to death of perennial ryegrass.  The period of significant yellowing and/or bare patches lasted from 5 weeks to greater than 9 weeks, depending on the treatment tested.  In this coastal environment with its very gradual spring/summer warming trend, significant yellowing of 5 weeks or more should be expected with any of the products tested.  If the spring is unseasonably cool (prolonged periods with average temperatures below 65F), this period can be significantly extended.
  • No damage to hybrid or common bermudagrass was observed. However, due to its inherently slower growth rate, areas with common bermudagrass were slower to recover from herbicide applications than areas with hybrid bermudagrass.
  • Treatments made later in the year, when average air temperatures were greater than 65F, produced less severe yellowing of turf than applications made earlier in the year.  Based on the 30-year normal data for Morgan Run Golf Club (Table 1), this threshold temperature would typically be reached by mid-June.
  • The half rate (0.2 oz/1000 sq ft) of Revolver produced a less severe and a shorter duration of turf yellowing than the full rate, without any decrease in herbicidal activity.  While the lowered rate may result in decreased herbicidal activity for hard-to-kill weeds, the idea of reduced rates should be considered more seriously in geographic regions (such as coastal California) where the prolonged period of yellowing turf produced by sulfonylureas used at the full labeled rate may be unacceptable.  It may be that a slight loss in herbicidal activity would be a small price to pay if a significant reduction in turf yellowing accompanied it.
  • Overall, the best combination of results (increased bermudagrass stand with the smallest duration and least severe yellowing of turf) was produced when applications were timed at bermudagrass cover greater than 50%, when average air temperatures were 65F or higher, and/or when average soil temperatures (6” depth) were 70F or higher.  The data suggests the possibility that lowered product rates may help to reduce the period of turf yellowing while still providing acceptable ryegrass control (see above). These conclusions apply to the Southern California coastal climate under which this trial was conducted, and may not apply in other locations with different weather patterns.
  • Kerb is the current commercial standard for ryegrass removal.  It produced a more gradual transition to bermudagrass than either Revolver or Monument.  However, Kerb has the undesirable features of inconsistent performance (perhaps due to its inactivation in high organic matter [>4%] soils) and significant soil mobility. 
  • Variability on the golf course can produce varying results with sulfonylurea herbicides. In areas where bermudagrass cover is low and the percentage of cool season turf is high (greater than 50%), such as shaded, cool or wet areas, rye removal products are probably not a viable commercial option, unless long periods (8 weeks or more) of yellowing turf can be tolerated.  Likewise, during cool summers, bermudagrass cover may never reach the critical level to trigger herbicide applications.  Finally, the presence of common bermudagrass, which is an inherently slower growing turf than hybrid bermudagrass, will also result in a longer time period after application during which bare areas will persist.
  • For all of the reasons above, the benefits of sulfonylurea herbicides for rye removal on overseeded fairways in coastal California remain mixed, since the risk of yellowing fairways for 5 weeks or more may outweigh the benefits of improved bermudagrass stands.  The decision to use these products will depend on the golf course and the situation:
    • For golf courses that do not overseed, the benefits of sulfonylurea herbicides for control of rye, poa and other weeds are obvious and non-controversial.
    • For golf courses that are committed to improved bermudagrass stands and are willing to accept yellowing turf during June and July, these products have a definite benefit, especially if a multi-year commitment (see Project II below) to this process is made.
    • For golf courses that are looking for a quick and painless way to remove ryegrass from overseeded fairways, the benefits of sulfonylurea herbicides are less clear.  The rye can definitely be removed quickly by all of the products tested, but some pain will always be involved in the form of extended periods of yellowing turf.

Printable version of full report

Principal Investigators: Wendy Gelernter, Ph.D. and Larry J. Stowell, Ph.D., CPPP, CPAg

Cooperator:  Kevin Kienast, Morgan Run Golf Resort

Sponsors:  Chris Olsen, Bayer; Dean Mosdell, Syngenta


Management of Poa annua on Overseeded Fairways

Summary: Product labels for several preemergent herbicides currently contain warnings that applications made less than 4 months before overseeding may result in damage to turf. In other words, applications must be made no later than June—too early to obtain season long control in Southern California. Data from the southeastern U.S. suggests that both Ronstar and Barricade can be applied as late as 6 - 8 weeks before overseeding without damaging emerging ryegrass. This replicated trial was set up to confirm these results under southwestern weather and turf management conditions and to investigate the following questions:

  1. Which herbicides can be applied closest to the overseeding date, without damaging turf?
  2. Which herbicides provide the best control of Poa annua? 

Key results include the following:

  • If the correct rates of pre-emergence herbicides are used (50-100 lbs/A Ronstar G, less than 2 lb/A Barricade 65 G), these products can be applied much closer to overseeding (4 - 8 weeks before overseeding) than their labels currently indicate. This strategy will result in little or no turf damage, and good weed control through April or May, or as much as 9 months post-application.
  • Of the thirty-six different treatments that were evaluated, the best poa control was observed with both pre-emergence herbicides (Ronstar and Barricade) and the post-emergent herbicide Prograss.
  • Turf quality (damage to ryegrass) was significantly influenced by the rate of Ronstar G used, with a significant negative correlation between rate and turf quality. Interestingly, the timing of application of Ronstar G had little negative impact on turfgrass quality, even when applications were made 10, 8, 6, 4 and 2 weeks before overseeding.
  • Higher rates of pre-emergence herbicides (Ronstar G at >100 lb/A and Barricade 65 G at 2 lb/A) caused severe damage to ryegrass when applied 2 - 10 weeks before overseeding.
  • Split applications of Ronstar (50 lb/A, 4-8 weeks before overseeding and 100 lb/A 6-12 weeks after overseeding) provided excellent poa control, with consistent lack of phytotoxicity. This strategy appears to be the most likely to ensure good weed control, without any concomitant damage to turf.

Printable version of full report

Principal Investigators: Wendy Gelernter, Ph.D. and Larry J. Stowell, Ph.D., CPPP, CPAg

Cooperator:  Bill Kostes, Desert Dunes Golf Club

Sponsors: AgrEvo, Hi-Lo GCSA, Novartis, Rhone-Poulenc


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