March 2015

SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.

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50 SportsTurf | March 2015 Q&A with Dr. Grady Miller What are the benefits of using a plant growth regulator (e.g. Primo)? If there are thin areas of turfgrass cover, should one wait until it is more grown in to apply the Primo or does the Primo promote enough lateral growth in the bermudagrass that it will fill in just as fast being sprayed? — STMA member from Richmond, VA T he primary benefit to using plant growth regulators (PGRs) is to reduce mowing. Since mowing is one of the greatest expenses with turfgrass main- tenance, reducing mowing frequency and still maintaining turf quality can save significant fuel costs plus result in less wear over time on mowers. If you are not currently using PGRs, I would suggest that you give them a try. PGRs have not been as widely used in sports turf management as on golf courses or utility areas so it may surprise some to know that they have been actively used for more than 40 years. A common negative with the first PGRs was turf discoloration and damage. The popularity of PGRs increased in the 1980s with the introduc- tion of paclobutrazol (Trimmit and TGR Turf Enhancer) and flurprimidol (Cutless), which were safer on the turf than the earlier products. After trinexapac-ethyl (Primo) was introduced in the 1990s, the interest in their use went to an entirely new level, with greater acceptance on highly maintained turfgrasses such as those found on golf courses and athletic fields. The PGRs are regulated the same as pesticides. They also are governed by the same patent laws. The active ingredients found in the common PGRs are off-patent so this has increased their availability as generic products. Trinexapac-ethyl con- tinues to be the most common PGR active ingredient used on high-quality bermuda- grass. You mentioned Primo, which was the product trade name of the original trinexapac-ethyl. But now trinexapac-ethyl is also sold as Armor Tech, Goldwing, Governor, Groom, Podium, PrimeraONE Trinexapac-Ethyl, Primo, Promo MAXX , RegiMax, Solace, T-Nex, T-Pac, and Triple Play. Like other turf products, the active ingredient may be mixed with other chem- icals and sold under a unique trade name. Trinexapac-ethyl is a foliar-absorbed product that works by inhibiting the late- stage gibberellin synthesis in turfgrasses. Gibberellins are plant-produced hormones that are needed for cell elongation and normal growth. When gibberellin produc- tion is inhibited, plant cells do not elongate, stem length is shortened, and overall plant growth and growth rate are reduced. The result is a darker turfgrass with increased density. Trinexapac-ethyl is not very effec- tive in seedhead suppression compared to some of the others. In addition, trinexapac- ethyl generally does not suppress weed growth, particularly broadleaf weeds. Trinexapac-ethyl has been shown to reduce common and hybrid bermudagrass clipping weights by 50 percent at 7 days after application. Depending upon appli- cation rates, it may provide some level of suppression for 4 to 8 weeks. The slowed growth can also dramatically reduce the chance of scalping. This can be a sig- nificant management advantage during periods of high rainfall that can result in missed mowing cycles. When the effects of trinexapac-ethyl begin to "wear-off " there is usually an increase growth rate unless it is reapplied. This is typically referred to as "rebound effect." At typical use rates, it is recommended that repeat applications be made at approximately 4-week intervals throughout the active growth period so this rebound effect is not experienced. Trinexapac-ethyl is a low-use rate prod- uct, with the active ingredient application rates from 0.05 to 0.5 pounds per acre. Amount of formulation used per acre can vary widely depending on formula- tion, turfgrass, etc., so carefully read the label. For example, Governor is a granular product and has an upper broadcast rate of more than 200 pounds of product per acre; whereas the liquid Primo MAXX may be sprayed at just a few fluid ounces per acre. It should also be noted that PGRs should not be applied before bermudagrass is actively growing following green-up. Apply it too early and expect some discoloration. Some of the bronze-colored discoloration can be offset with light applications of soluble iron and/or nitrogen, which I would recom- mend. It is only the year's first application of PGR that normally has the discoloration issue, not subsequent applications. Studies and experience have shown that trinexapac-ethyl should only be applied to healthy turfgrass. While it may increase rooting, it does not promote increased lat- eral growth. When applied to sparse stands, it may take longer for the turfgrass to fill in bare areas. The use of trinexapac-ethyl has been shown to promote better drought and heat tolerant as well as an increase in shade tolerance when applied to healthy grass before the onset of these stresses. For sports turf managers the other significant use of trinexapac ethyl is as a bulk paint additive. The rate for Primo MAXX in paint is 1 ounce per gallon of marking paint mix to treat approximately 1,000 square feet of line surface area. Not having to paint lines so often is a huge benefit. Note that there are differential responses to trinexapac ethyl among grasses and cultivars. So, it may be help- ful to start at a moderate rate and then try increasing rates until you determine the one that maximize growth suppression of your turfgrass while still maintaining high quality. Try it. I think this will be one regu- lation you really like. ■ ST When regulation can be good Questions? Send them to Grady Miller at North Carolina State University, Box 7620, Raleigh, NC 27695-7620, or email Or, send your question to David Minner at Iowa State University, 106 Horticulture Hall, Ames, IA 50011 or email Professor, North Carolina State University

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