ethyl treated plots and the untreated. Given these results, the inference may be made that divot recovery on creeping bentgrass maintained at putting green height would not be
impacted either positively or negatively by trinexapac- ethyl treatments.
Aerification (Coring) Hole
Recovery: In a series of studies looking at both trinexapac-ethyl and paclobutrazol we found no difference in core hole recovery with trinexapac- ethyl applied at 4ml per 100m2
Table 1: Plant hormones and their function. Group Auxin
Chemical Example Gibberellins Cytokinin Ethylene
Gibberellic Acid, GA3, GA1
Zeaton Gas Abscisic Acid Single compound on a 7-day schedule,
nor with paclobutrazol applied at 0.14kg per ha and 0.07 kg per ha1 on a 14 day schedule. As a note of caution both studies were conducted from late summer through early fall. Physiological impacts: Applications of trinexapac- ethyl have also shown that there is a positive impact on colour of turfgrass canopies, and this has occurred across many studies. The dark greening of the grass surface that occurs from repeated applications has found favour with players and golfers alike. The other major angle of research in the use of growth regulators is improving tolerance of shaded turfgrasses. Turfgrass in shaded conditions elongates and loses density which leads to loss of wear tolerance. It is a problem for stadium and golf course managers alike. There are some succinct differences though; neutrally shaded sites such as stadiums have loss of light intensity compared to golf courses shaded by mature tree lines which impact light quality. The change in the light has different impacts on plants both considered negative. The loss of light quantity however is of major concern and it has been shown that repeated applications of trinexapac-ethyl have delayed the loss of turfgrass cover in shaded conditions. This has been successful in as high as 80% reduced light on certain species. Research Implications:
From our studies it appears that repeated use of trinexapac-ethyl has no detrimental affects on turfgrass recovery from divoting or coring. The use of the growth regulator has also proved beneficial in managing turf in shaded conditions and it is a tool that is open to all turfgrass managers both in the United States and the United Kingdom.
Syntheses location
Indole-3-acetic acid (IAA) Leaf primoridia and young leaves
Young tissue and developing seeds
Root tips and developing seeds
Leaves, shoots
Description
Important in inhibiting leaf senescence and phloem and xylem differentiation.
elongation. These chemicals are classified according to structure (ex. GA3) rather than biological activity.
Promote cell division and delay leaf senescence. Used as a growth promoter in tissue culture.
Ethylene is a gas that forms in tissue that is undergoing stress. It is important in the fruit ripening process. In turf, with enhanced release, decreased cell size occurs.
Mature leaves under stress Generally thought of as an inhibitor of growth. It closes stomata under moisture stress and counteracts some of the effects of auxins and gibberellins.
Table 2. Description of the major Plant Growth Regulators (PGR) used on high quality cool season turf. (Note: The only available PGR in the UK is Primo Maxx®
).
Common Name Trade Name Absorption Mode of Action (U.S.)
Mefluidide Ethephon Embark Proxy Foliar Foliar Comments
Inhibits cell division (mitosis) Primary used to inhibit Poa annua and differentiation in meristematic tissue
Enhances the release of ethylene into the plant
Paclobutrazol Trimmit Root
Early gibberellic acid (GA) inhibitor
Flurprimidol Cutless Root
Early gibberellic acid (GA) inhibitor
regulating growth through its seedhead control. influence on cell size.
Used alone or in combination with trinexapac-ethyl for Poa annua
the gradual reduction of Poa annua in creeping bentgrass turf (golf course fairways). Due to the greater inhibitory affect on Poa annua.
paclobutrazol. With both paclobutrazol and flurprimidol conversion to more bentgrass in fairways is accomplished with spring and fall applications at the higher end of the recommended rate.
Trinexapac-ethyl Primo MAXX Foliar
Late gibberellic acid (GA) inhibitor
fine high quality turf. Implicated in enhancing summer stress tolerance of turf, reduced disease severity (in some cases) and improved turf quality.
Figure 1 (main picture). The majority of plant growth regulator studies have been conducted on USGA constructed greens established to ‘Penncross’ creeping bentgrass located at the Ohio Turfgrass Foundation Research and Educational Facility, Columbus, Ohio. The greens were mowed at a height of 3.1 mm.
Figure 2 (left). The divot recovery study.
Figure 3 (below). Shade cloth was used to enclose creeping bentgrass turf to look at the impact of neutral shade on turfgrass growth with plant growth regulators.
Most widely used plant growth regulator on Originally used in the same fashion as The GA inhibitors were and still are used in
spring prior to seedhead inflorescence emergence.
seedhead formation. Application made in Promotes stem elongation through cell division and Promote growth through cell division and elongation.
About the author: Professor Karl Danneberger Ph. D. works in the Department of Horticulture and Crop Science at the Ohio State University. He was assisted in his research by Edward Nanglel and Aneta Studzinska, Graduate Research Assistants and Arly Drake, Undergraduate Research Assistant
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