GROWTH REGULATORS
I
n the last 30 years, plant growth regulator (PGR) use has progressed from a marginal or niche application to an integral part of golf course management programmes. In the early 1980s mefluidide (Embark®
) was the first plant
growth regulator widely used on fine quality turf. Mefluidide was, and still is, primarily used on Poa annua or Poa annua containing fairways for seedhead control in the cool temperate regions. An application timed properly prior to seedhead emergence could provide over 90% seedhead control. It suppresses growth and seedhead formation through inhibition of cell division (mitosis) in the meristematic region of the plant. Due to its mode of action, mefluidide was characterised as a Type I compound.
In the mid 1980s two
additional PGRs - flurprimidol (Cutless® (Trimmit®
) and paclobutrazol ) - became available.
These were different from mefluidide in their mode of action (Table 2). The newer PGRs, including flurprimidol, paclobutrazol, trinexapac-ethyl
38
and ethephon (an older chemistry but relatively new to turf), work to inhibit or enhance plant hormones (Table 1). Gibberellic acid (GA) inhibitors like flurprimidol and paclobutrazol are not very effective for seedhead suppression. Due to the lack of seedhead control and root absorption these PGRs were classified as Type II compounds. Initially, both flurprimidol and paclobutrazol were used in creeping bentgrass/Poa annua fairway conversion. The GA inhibitors have a greater growth inhibiting effect on Poa annua than creeping bentgrass. Once applied Poa annua growth was suppressed to a greater extent than the creeping bentgrass. This suppression difference allowed the creeping bentgrass to literally grow “over the top” of the Poa annua.
In the early 1990s the
release of trinexapac-ethyl (Primo®
) ushered in a new era
of PGR use. Trinexapac-ethyl was not a true Type II PGR. It was foliar absorbed and was a late GA inhibitor. Reclassification of the plant growth regulators into Type A
through E groups has been proposed. Trinexapac-ethyl catalyzed the use of PGRs from a couple of niche applications a year to multiple applications throughout the growing season. Its use has, in many ways, changed how turfgrass is maintained in the United States. Although the use of trinexapac-ethyl reduced the amount of growth, and thus clippings, combined with mowing, the overall quality of the turf improves (6). Repeated applications of trinexapac-ethyl was found to enhance the summer stress tolerance of the turf. In the temperate region of the United States we found from surveying 90 golf course superintendents, 84% of the respondents used PGRs for greens management. In the United Kingdom a 4-week application interval is recommended (as with any chemical compound always follow the label directions). In our survey we found weekly (7- day) or biweekly (14-day) applications of PGRs at reduced rates for greens management accounted for 85% of the applications. Given the frequent applications of
Their impact on golf course management By Professor Kark Danneberger Ph. D, Ohio State University
trinexapac-ethyl on golf greens, we wanted to look at the continual use of trinexapac- ethyl on divot and aerification (coring) hole recovery.
Divot Recovery
The development of high shoot density creeping bentgrass cultivars and the subsequent use on fairways has raised concerns on how these new cultivars will respond to trinexapac-ethyl treated turf and subsequent divot recovery. The high shoot density creeping bentgrass cultivars tend to produce dense upright shoot growth with little horizontal stem (stolon) growth. We conducted a study on an L93 creeping bentgrass turf maintained at 1.2 cm height of cut during the summer of 2001. Trinexapac- ethyl (Primo MAXX®
applied at 8ml per 100m2
) was .
Three days after application six divots were made by hitting golf balls in each plot. Divot size, as measured by the length and width, was recorded weekly. Regarding divot recovery as measured by the size of the divot over time, we did not find any significant difference between trinexapac-
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