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Key Takeaways

  • Plant growth regulators (PGRs) are often used in putting green management for a variety of reasons.
  • There are both planned and unintended results from PGR use in putting green management.
  • Daily collection of clipping yield from putting greens can guide fertility, management and PGR programs.
  • Managing creeping bentgrass putting greens without PGRs has been a very successful practice for many in the Transition Zone.
  • Plant growth regulators are not needed to provide high-performing creeping bentgrass putting greens.

While turfgrass management and greenkeeping have been around for a long time, modern turfgrass science is relatively young and continues to evolve. What we think we know or understand is often replaced with new research and experience from practical application. When new information becomes available, turfgrass managers shouldn’t be afraid to change in order to improve.

Changing paradigms

A good example of the constant evolution in turfgrass management occurred earlier this year when the paper “Soil pH – Nutrient Relationships: The Diagram” (Hartemink & Barrow, 2023) was published in the scientific journal Plant and Soil. This paper outlined the fallacies and lack of specificity presented by the soil pH diagram that was first published in 1946 by Emil Truog and has been widely used in agriculture, soil science and turfgrass management courses ever since.

Other evidence of evolving turfgrass management exists in the area of soil fertility. Strategies described by the soil fertility theory of Minimum Levels for Sustainable Nutrition (MLSN) have been widely adopted in the academic and golf course management communities. MLSN has replaced strategies borrowed from crop production including the approach known as Sufficiency Level of Available Nutrients (SLAN). Ironically, many of the SLAN strategies used in turfgrass management (Carrow, 2004) were researched and described by the same researchers who helped develop MLSN (Woods et al. 2020). The researcher’s understanding of fertility management shifted as the research bore out new information.

What about plant growth regulators?

The examples above show how much accepted turfgrass management paradigms have changed in recent years. Now let’s shift our focus to rethinking the use of plant growth regulators (PGRs) on creeping bentgrass putting greens. Without doubt, PGRs have helped to improve many aspects of putting green management, but those improvements are not without costs. The stress on bentgrass putting greens during summer in many parts of the U.S. is already considerable and PGR applications may not be helping matters. A growing body of research and practical experience suggests that discontinuing PGR use on bentgrass greens for part or all of the year in certain areas can lead to improved turf health and playing conditions.

"A growing body of research and practical experience suggests that discontinuing PGR use on bentgrass greens for part or all of the year in certain areas can lead to improved turf health and playing conditions."

PGRs have been widely used to manage golf course turfgrasses for the last 20-25 years. They are used to suppress or manipulate turfgrass growth, usually in low doses. Dr. Tom Watschke first classified PGRs in 1985 into Type I PGRs that affect growth and development and Type II PGRs that suppress growth. Since then, further research has led the scientific community to accept the following classifications of PGRs:

Class A: Late-step gibberellic acid inhibitor (trinexapac-ethyl, prohexadione calcium)

Class B: Early-step gibberellic acid inhibitor (paclobutrazol, flurprimidol)

Class C: Cell division inhibitors (mefluidide)

Class D: Herbicides (glyphosate)

Class E: Hormones (ethephon)

Class F: Natural products (kelp, humics)

Class A and B are what most turfgrass managers think of as “true” PGRs. These products interfere with turfgrass’ hormonal status by interrupting the gibberellin biosynthesis pathway and reducing gibberellic acid production. Gibberellic acid stimulates cell growth and elongation in turfgrass and a reduction in gibberellic acid reduces the rate of turfgrass growth. The production of gibberellic acid also impacts other turfgrass hormone levels including abscisic acid – a stress defense hormone – and cytokinin, which is a growth rate hormone.

There are many benefits to reducing growth during optimal growing conditions, including reducing the need for mowing and improving mowing quality. PGRs are also used to improve the density and leaf texture of turfgrasses, which can lead to better playing conditions. Research and practical experience provide evidence of the benefits of PGR use. However, just like the Truog diagram, the specificity of PGR use and the performance of PGR programs in various regions and climates has not been adequately studied.

Plant growth regulators and creeping bentgrass

Creeping bentgrass is a cool-season turfgrass that is best adapted for growth when air temperatures are between 60-75 degrees Fahrenheit. Creeping bentgrass has been used on golf course putting greens for many decades in climates of marginal adaptation. These regions, including the mid-Atlantic and southeastern U.S., consistently see hot, humid conditions in the summer months, leading to poor creeping bentgrass conditions. While many golf courses in these regions have converted putting greens to ultradwarf bermudagrass, the use of creeping bentgrass is still prominent.

PGRs are used to slow down growth of creeping bentgrass putting greens (Class A and B) and reduce Poa annua competition (Class B). Under optimal growing conditions, PGRs can successfully be used to improve putting green speed, smoothness and other qualities. Under suboptimal growing conditions – e.g., high heat and humidity – PGRs can increase stress on creeping bentgrass, delaying recovery and negatively impacting stress defense systems in the plant. Many golf courses in the mid-Atlantic and Southeast with creeping bentgrass putting greens have successfully removed PGRs from their management programs in the heat of summer or throughout the entire year with huge improvements in turfgrass health and performance. Golf course superintendents in these regions need to evaluate if PGRs are negatively impacting their creeping bentgrass performance at certain times of the year and whether changes could lead to resource savings and improved turf quality.

" Under suboptimal growing conditions – e.g., high heat and humidity – PGRs can increase stress on creeping bentgrass, delaying recovery and negatively impacting stress defense systems in the plant."

Advantages of using PGRs in creeping bentgrass management programs

  1. If Poa annua invasion is a primary concern in your creeping bentgrass management, Class B PGRs can give creeping bentgrass a competitive advantage. These programs are most successful in the fall, when Poa annua germination is at its highest.
  2. PGRs will reduce growth and can create a more diminutive growth habit, leading to faster putting greens.
  3. There is evidence of improved turfgrass conditions in shade with the use of PGRs.

Advantages of removing PGRs from your creeping bentgrass program

  1. Reducing inputs and stress factors during periods of high heat and humidity are clear advantages. There is enough working against successful creeping bentgrass management in hot, humid regions. Removing a product that manipulates turfgrass growth and recovery will reduce stress and improve plant health.
  2. Improved feedback from data collection is another advantage. PGRs limit a turfgrass manager’s understanding of how fertilizer, fungicide, water, weather and cultural programs impact turfgrass growth. Understanding the growth impacts of your programs and various environmental conditions is critical to successful putting green and resource management. Superintendents using PGRs often do not observe significant changes in growth and therefore miss opportunities to make positive adjustments to their management programs.
  3. PGRs may have a negative impact on creeping bentgrass competition against crabgrass and goosegrass. Ongoing research at Virginia Tech indicates that Class A PGR use leads to an increase in these grassy weeds compared to putting greens that are not treated with PGRs.
  4. Many golf courses have seen improved conditions and performance of creeping bentgrass putting greens with the elimination of PGR use. They have also seen a reduction in fertilizer and spray applications, along with improved control of summer grassy weeds.

Things to consider

PGR programs are often successful when conditions are optimal for creeping bentgrass growth. If environmental conditions are not suited for creeping bentgrass, PGRs can have a negative impact on putting green performance and plant health.

Removing PGRs from putting green management programs will not be easy for some superintendents. PGRs reduce flushes of growth and the demands for consistently fast putting green speed require the use of PGRs at some golf courses. These demands place golf course superintendents on the tipping point of plant health and can lead to turfgrass loss. Balancing the expectations at your property with turfgrass health and sustainability is a very site-specific challenge.

Many golf courses have provided excellent creeping bentgrass putting greens without PGRs. How do they do it?

  1. Focusing on data collection – including clipping volume, maintenance inputs like mowing and rolling, and ball roll – can help you effectively manage growth without PGRs. Daily data collection without the influence of PGRs leads to a better understanding of how inputs and environmental conditions influence growth. In turn, this can help you identify and implement strategies other than PGR applications to manage growth. The USGA articles “A Quick-Start Guide to Putting Green Data Collection” and “Addressing Common Concerns About Putting Green Data Collection” can help you begin or refine a putting green data collection program.
  2. Fertility management is a critical part of successfully removing PGR use during part or all of the year. Use soil testing and MLSN guidelines to manage turfgrass nutrition with minimal inputs. Nitrogen fertility should be managed using growth potential, soil temperatures, growth rate and anticipated nitrogen release from organic matter breakdown.
  3. Setting clear expectations for putting green speed during heat and humidity is also important. PGRs may be used in the fall without compromising turfgrass health. Removing them from the program in summer will likely improve turf health, but additional growth could have an impact on green speed. Speeds may need to be slower in the summer to relieve plant health concerns associated with PGR applications during periods of heat and humidity.

Start small by stopping PGR use during stressful times of the year on a practice green or nursery green. Collect data on that green and compare those metrics with other greens that are still receiving PGR applications. As you begin to understand the differences, you can adjust management practices to deliver the desired conditions with new techniques. When you feel ready, expand the program.


The thought of removing PGRs from your bentgrass putting green management program may be intimidating or stressful. Evaluating the impact of removing PGRs and mastering bentgrass growth management without PGRs may take months or multiple growing seasons. However, many successful superintendents at high-level golf courses have removed PGRs during part or all of the year with great results.


Carrow, R. N. 2004. Clarifying soil testing: III. SLAN sufficiency ranges and recommendations. Golf Course Management. 72(1):194-198.

Hartemink, A.E., and N.J. Barrow. 2023. Soil pH - Nutrient relationships: The diagram. Plant Soil.

Woods, M. S., L. Stowell, and W. Gelernter. 2020. A survey of soil nutrient analyses from turfgrass sites in Asia, Europe, and North America. Asian Turfgrass Center.