{"id":102165,"date":"2026-08-25T21:31:43","date_gmt":"2026-08-25T21:31:43","guid":{"rendered":"https:\/\/www.greenkeeperapp.com\/marketing\/?p=102165"},"modified":"2026-08-25T22:23:44","modified_gmt":"2026-08-25T22:23:44","slug":"when-60-regulation-still-isnt-enough","status":"publish","type":"post","link":"https:\/\/www.greenkeeperapp.com\/marketing\/index.php\/when-60-regulation-still-isnt-enough\/","title":{"rendered":"When 60% Regulation Still isn’t Enough"},"content":{"rendered":"\n[et_pb_section fb_built=”1″ _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”][et_pb_row _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”][et_pb_column type=”4_4″ _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”]

Summer Created a Misleading Growth Surge<\/h4>\n

It has been a hot, humid summer across much of the U.S., and one of the most common questions we\u2019ve received is some version of: \u201cWhy is my PGR program not working anymore?<\/em><\/strong>\u201d<\/span><\/p>\n

The evidence is usually sitting in the mower baskets.<\/span><\/p>\n

Bentgrass greens have continued to produce surprisingly high clipping volumes, even during periods when the PACE Growth Potential model<\/a><\/strong> indicates that growing conditions are far from ideal.<\/span><\/p>\n

Aboveground, the turf appears to be growing aggressively. Belowground, it may be running out of energy.<\/span><\/p>\n

Warm soils, adequate moisture and humid summer weather increase microbial activity and the mineralization of nitrogen from soil organic matter. That additional nitrogen can stimulate rapid leaf growth, particularly following heavy rainfall. At the same time, high temperatures increase plant respiration and reduce the amount of sugar the plant can retain after accounting for its metabolic demands.<\/span><\/p>\n

The result is a situation we have seen repeatedly this summer: high clipping yield during a period of poor plant carbon balance.<\/span><\/p>[\/et_pb_text][et_pb_divider _builder_version=”4.21.0″ _module_preset=”default” hover_enabled=”0″ sticky_enabled=”0″][\/et_pb_divider][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”]

High ClipVol Does Not Always Mean Healthy Growth<\/span><\/h4>\n

The PACE Growth Potential model is often interpreted as a clipping-yield model, but I find it more useful as a theoretical indicator of sugar production. The model assumes that cool-season turfgrass is most efficient near its optimum temperature and that potential growth declines as temperatures move above or below that point.<\/span><\/p>\n

Field clipping yield does not always follow the same pattern. Bentgrass remains highly responsive to nitrogen, moisture and other growth stimuli during hot weather. When measured ClipVol is high while PACE Growth Potential is low, the plant may be using stored carbohydrates to support leaf growth that current photosynthesis cannot sustain.<\/span><\/p>\n

That imbalance may be manageable for a few days. Sustained over several weeks\u2014as it has been in many locations this summer\u2014it becomes increasingly damaging.<\/span><\/p>[\/et_pb_text][et_pb_image src=”https:\/\/www.greenkeeperapp.com\/marketing\/wp-content\/uploads\/2026\/08\/fig4b_regional_gp_marketing.jpg” _builder_version=”4.21.0″ _module_preset=”default” title_text=”fig4b_regional_gp_marketing” hover_enabled=”0″ sticky_enabled=”0″ align=”center” max_width=”90%” show_in_lightbox=”on”][\/et_pb_image][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”]

<\/span><\/p>\n

Producing leaves requires carbohydrates and nutrients. Mowing then removes a portion of those resources from the turfgrass system. Excessive clipping production can therefore accelerate both sugar depletion and nutrient removal at the exact time roots, crowns and other growing points need those resources to survive environmental stress.<\/span><\/p>\n

The plant may look vigorous because the mower baskets are full, but it can actually be becoming less resilient. As we move toward the end of summer, that weakened turf can become more susceptible to disease, traffic injury and shade. Excessive growth can also reduce putting performance while increasing mowing requirements and nutrient demand.<\/span><\/p>\n

For practical purposes, cool-season turf can grow itself to death during summer.<\/span><\/p>\n

Plant growth regulators are among our best tools to prevent that from happening.<\/span><\/p>[\/et_pb_text][et_pb_image src=”https:\/\/www.greenkeeperapp.com\/marketing\/wp-content\/uploads\/2026\/08\/fig5_gp_response_marketing.jpg” _builder_version=”4.21.0″ _module_preset=”default” title_text=”fig5_gp_response_marketing” hover_enabled=”0″ sticky_enabled=”0″ align=”center” max_width=”90%” show_in_lightbox=”on”][\/et_pb_image][et_pb_divider _builder_version=”4.21.0″ _module_preset=”default” hover_enabled=”0″ sticky_enabled=”0″][\/et_pb_divider][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”]

Percent Regulation Is a Relative Number<\/span><\/h4>\n

One of the most common conclusions we\u2019ve heard this summer is, \u201cMy PGR program isn\u2019t working anymore.\u201d<\/span><\/p>\n

Usually, the evidence is increased clipping volume. The superintendent is applying the same PGR program that worked earlier in the season, but the baskets have been filling faster during the heat and humidity.<\/span><\/p>\n

The problem with that conclusion is that clipping volume and percent regulation measure two different things.<\/span><\/p>[\/et_pb_text][et_pb_image src=”https:\/\/www.greenkeeperapp.com\/marketing\/wp-content\/uploads\/2024\/03\/20230511_074006-scaled.jpg” _builder_version=”4.21.0″ _module_preset=”default” title_text=”20230511_074006″ hover_enabled=”0″ sticky_enabled=”0″ align=”center” max_width=”90%”][\/et_pb_image][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}” custom_padding=”||0px|||”]

Clipping volume is an absolute measurement of how much leaf tissue was produced. Percent regulation is a relative estimate of how much slower treated turf is growing compared with how it would have grown without the PGR.<\/span><\/p>\n

Consider two situations:<\/span><\/p>\n

    \n
  • If untreated turf would have produced 2.0 quarts of clippings per 1,000 square feet, 60% suppression would reduce measured ClipVol to 0.8 quart.<\/span><\/li>\n
  • If untreated turf would have produced 4.0 quarts, the same 60% suppression would still leave 1.6 quarts.<\/span><\/li>\n<\/ul>\n

    The PGR program provided the same relative suppression in both situations. However, the resulting clipping volumes\u2014and the management implications\u2014are very different.<\/span><\/p>\n

    Without an untreated check plot, it is impossible to directly observe how much grass would have been in the baskets without the PGR program. GreenKeeper\u2019s models provide that missing comparison by estimating both combined PGR suppression and potential clipping volume without the effects of PGRs and growth-regulating fungicides.<\/span><\/p>\n

    A summer increase in ClipVol does not necessarily mean the PGRs failed. In many situations this year, clipping production would have been dramatically worse without them.<\/span><\/p>[\/et_pb_text][et_pb_divider _builder_version=”4.21.0″ _module_preset=”default” hover_enabled=”0″ sticky_enabled=”0″][\/et_pb_divider][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”]

    A Season-Long Suppression Target Is Not the Goal<\/span><\/h4>\n

    Sustaining the same percentage of clipping-yield suppression for an entire season sounds logical, but it does not necessarily produce consistent turfgrass growth.<\/span><\/p>\n

    The actual management objective should be to maintain an appropriate absolute growth rate.<\/span><\/p>\n

    If the untreated growth rate doubles during summer, maintaining the same 30% or 40% regulation will allow measured ClipVol to increase substantially. That excess growth continues to remove sugars and nutrients even though the PGR program is technically producing its expected response.<\/span><\/p>\n

    During a summer growth surge, managers may need to:<\/span><\/p>\n

      \n
    • Shorten PGR application intervals as products are metabolized more rapidly.<\/span><\/li>\n
    • Increase application rates within label directions.<\/span><\/li>\n
    • Combine PGR active ingredients to produce greater cumulative suppression.<\/span><\/li>\n
    • Reduce unnecessary nitrogen applications.<\/span><\/li>\n
    • Continue monitoring measured ClipVol rather than assuming a calendar-based program is adequate.<\/span><\/li>\n<\/ul>[\/et_pb_text][et_pb_image src=”https:\/\/www.greenkeeperapp.com\/marketing\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-25-154323.png” _builder_version=”4.21.0″ _module_preset=”default” title_text=”Screenshot 2026-08-25 154323″ max_width=”80%” align=”center” hover_enabled=”0″ sticky_enabled=”0″ show_in_lightbox=”on”][\/et_pb_image][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”]

      Research has shown that single PGR applications commonly suppress cool-season putting-green clipping yield by approximately 15% to 45%, depending on the active ingredient and rate. Combining active ingredients can produce much greater suppression. In one creeping bentgrass study, a labeled combination of a Class A and Class B PGR produced approximately 55% to 70% suppression.<\/span><\/p>\n

      That degree of regulation may sound excessive during spring or fall. As many managers have seen this summer, it can be exactly what is required during a midsummer growth surge.<\/span><\/p>[\/et_pb_text][et_pb_divider _builder_version=”4.21.0″ _module_preset=”default” hover_enabled=”0″ sticky_enabled=”0″][\/et_pb_divider][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”]

      Let Clipping Volume Determine How Hard You Push<\/span><\/h4>\n

      Clipping volume should be the primary feedback mechanism for adjusting a summer PGR program.<\/span><\/p>\n

      Measure clippings from the same representative greens as consistently as possible and follow the five-day average in GreenKeeper. The average reduces daily noise from mowing schedules, rainfall, equipment and other short-term factors. Establish a ClipVol range that provides the desired balance among turf quality, recovery, green speed and stress tolerance.<\/span><\/p>\n

      Then ask two different questions:<\/span><\/p>\n

        \n
      1. Is the measured clipping volume acceptable?<\/span><\/li>\n
      2. How much higher would clipping volume be without the PGR program?<\/span><\/li>\n<\/ol>\n

        The first question determines whether the turf is growing at the desired rate. The second reveals whether the PGR program is providing the expected regulation.<\/span><\/p>[\/et_pb_text][et_pb_image src=”https:\/\/www.greenkeeperapp.com\/marketing\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-25-155524.png” _builder_version=”4.21.0″ _module_preset=”default” title_text=”Screenshot 2026-08-25 155524″ align=”center” max_width=”80%” hover_enabled=”0″ sticky_enabled=”0″][\/et_pb_image][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”]

        GreenKeeper also allows managers to compare fertilizer applications with estimated nutrient removal in clippings. This is especially useful during summer because some of the nitrogen driving growth may be coming from soil organic matter rather than recent fertilizer applications. Applying additional nitrogen simply because the turf appears stressed can compound the problem when mineralized soil nitrogen is already stimulating excessive leaf growth.<\/span><\/p>\n

        When ClipVol is high, visual turf quality is acceptable and nutrient removal is elevated, additional nitrogen is unlikely to be the first solution. Greater growth regulation may be more appropriate.<\/span><\/p>[\/et_pb_text][et_pb_divider _builder_version=”4.21.0″ _module_preset=”default” hover_enabled=”0″ sticky_enabled=”0″][\/et_pb_divider][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”]

        Increasing Summer PGR Intensity<\/span><\/h4>\n

        Actively growing turf generally provides more flexibility to use higher labeled PGR rates than slow-growing turf. This is particularly true when the turf has already received repeated applications of the active ingredients and rates are increased progressively.<\/span><\/p>\n

        That does not eliminate phytotoxicity risk. Grass species, mowing height, environmental stress, active ingredient and application history all matter. The safest approach is to gradually increase regulation while monitoring clipping volume, color, quality and recovery.<\/span><\/p>[\/et_pb_text][et_pb_image src=”https:\/\/www.greenkeeperapp.com\/marketing\/wp-content\/uploads\/2021\/12\/ud-primo-damage-plot.png” _builder_version=”4.21.0″ _module_preset=”default” title_text=”ud-primo-damage-plot” align=”center” max_width=”60%” hover_enabled=”0″ sticky_enabled=”0″][\/et_pb_image][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”]

        Now, as we move toward fall, the opposite approach becomes increasingly important. As temperatures cool, PGR activity lasts longer and natural turfgrass growth begins to slow. Continuing midsummer rates and intervals can cause products to stack, leading to excessive suppression, discoloration and reduced wear tolerance.<\/span><\/p>\n

        The summer program should therefore have an intentional ramp up and an equally intentional ramp down.<\/span><\/p>[\/et_pb_text][et_pb_image src=”https:\/\/www.greenkeeperapp.com\/marketing\/wp-content\/uploads\/2026\/08\/fig6_intervals_marketing.jpg” _builder_version=”4.21.0″ _module_preset=”default” title_text=”fig6_intervals_marketing” align=”center” max_width=”90%” hover_enabled=”0″ sticky_enabled=”0″ show_in_lightbox=”on”][\/et_pb_image][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”]

        What Data-Driven PGR Management Looked Like in Practice<\/span><\/h4>\n

        From 2021 through 2023, when I was actively managing putting greens on a golf course, I adjusted the PGR program throughout the season rather than maintaining one rate or mixture from spring through fall.<\/span><\/p>[\/et_pb_text][et_pb_image src=”https:\/\/www.greenkeeperapp.com\/marketing\/wp-content\/uploads\/2026\/08\/20210709_123757-scaled.jpg” _builder_version=”4.21.0″ _module_preset=”default” title_text=”20210709_123757″ align=”center” max_width=”90%” hover_enabled=”0″ sticky_enabled=”0″][\/et_pb_image][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”]

        The program generally began with Proxy during the annual bluegrass seedhead period, followed by Proxy plus Anuew. As the seedhead window ended and summer growth increased, I transitioned to Anuew plus a low rate of Trimmit.<\/span><\/p>\n

        Anuew provided the consistent Class A foundation. Trimmit became the adjustable component I used to respond to changes in clipping volume.<\/span><\/p>\n

        I gradually increased Trimmit rates as temperatures, rainfall and soil nitrogen mineralization increased. By midsummer, I would use the maximum labeled Trimmit rate when necessary. In mid-July, combined expected suppression would frequently reach 60% to 70%.<\/span><\/p>\n

        Even with that amount of regulation, the mower baskets were not always light. That did not mean the PGR program had stopped working. GreenKeeper\u2019s estimate of clipping volume without PGRs showed how much greater growth would likely have been without the program.<\/span><\/p>\n

        That information was critical to my decision making. Without the clipping data, nutrient-removal estimates and modeled PGR response, I would have been largely guessing at whether to increase rates, shorten intervals, change mixtures or back off. The data gave me confidence to make those adjustments while still maintaining high-performing putting surfaces.<\/span><\/p>[\/et_pb_text][et_pb_image src=”https:\/\/www.greenkeeperapp.com\/marketing\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-25-161542.png” _builder_version=”4.21.0″ _module_preset=”default” title_text=”Screenshot 2026-08-25 161542″ align=”center” max_width=”80%” hover_enabled=”0″ sticky_enabled=”0″ show_in_lightbox=”on”][\/et_pb_image][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”]

        I monitored the five-day clipping-volume average and reviewed nutrient removal relative to nutrient applications each month. GreenKeeper\u2019s proprietary PGR models helped me understand:<\/span><\/p>\n

          \n
        1. The expected combined suppression from the different active ingredients, rates and application timings.<\/span><\/li>\n
        2. The amount of clipping volume that likely would have been produced without the PGR program.<\/span><\/li>\n<\/ol>\n

          Those data made it possible to manage the turf\u2019s actual growth response rather than relying on a fixed spray interval or assuming that full mower baskets represented PGR failure.<\/span><\/p>[\/et_pb_text][et_pb_image src=”https:\/\/www.greenkeeperapp.com\/marketing\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-25-161531.png” _builder_version=”4.21.0″ _module_preset=”default” title_text=”Screenshot 2026-08-25 161531″ align=”center” max_width=”80%” hover_enabled=”0″ sticky_enabled=”0″ show_in_lightbox=”on”][\/et_pb_image][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” hover_enabled=”0″ global_colors_info=”{}” sticky_enabled=”0″]

          As nights cooled and daylength shortened, natural growth began to decline. PGR suppression also lasted longer in the cooler weather. I responded by progressively lowering Trimmit rates and eventually removing the Class B component rather than carrying the midsummer program into fall.<\/span><\/p>\n

          The objective was never to maintain 60% or 70% suppression. The objective was to maintain the right amount of growth for healthy, consistent and high-performing putting surfaces.<\/strong><\/p>[\/et_pb_text][et_pb_divider _builder_version=”4.21.0″ _module_preset=”default” hover_enabled=”0″ sticky_enabled=”0″][\/et_pb_divider][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”]

          Manage the Growth the Plant Can Afford<\/span><\/h4>\n

          Percent regulation only tells you how much the PGR program is slowing growth relative to untreated turf. It does not tell you whether the remaining growth rate is appropriate.<\/span><\/p>\n

          ClipVol tells you how fast the turf is actually growing. PACE Growth Potential provides context about the plant\u2019s theoretical ability to produce sugars under the current temperatures. Nutrient-removal estimates show what is leaving the system every time the greens are mowed.<\/span><\/p>\n

          Those measurements have been particularly important this summer, when low theoretical sugar production has repeatedly coincided with high nitrogen responsiveness and rapid clipping production.<\/span><\/p>\n

          This is when a fixed PGR program is least likely to be enough.<\/span><\/p>\n

          Use clipping volume to determine whether growth needs to be suppressed further. Use higher labeled rates, shorter weather-adjusted intervals and PGR mixtures when the situation requires them. Then, as nights cool and natural growth slows over the coming weeks, begin reducing that intensity rather than carrying the peak-summer program into fall.<\/span><\/p>[\/et_pb_text][et_pb_button button_text=”Let GreenKeeper App Help Manage Growth Rate” _builder_version=”4.21.0″ _module_preset=”default” button_alignment=”center” button_url=”https:\/\/www.greenkeeperapp.com\/marketing\/” hover_enabled=”0″ sticky_enabled=”0″][\/et_pb_button][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”]

          GreenKeeper connects measured ClipVol with PGR and DMI suppression models, fertilizer records, nutrient removal and weather. It cannot replace the superintendent\u2019s observations, but it can reveal what cannot be seen in the mower baskets: how hard the PGR program has actually been working and how much growth would likely have occurred without it.<\/strong><\/p>\n

          That insight provides confidence to regulate growth aggressively when summer conditions demand it\u2014and just as importantly, confidence to back off as those conditions finally begin to change.<\/strong><\/p>[\/et_pb_text][et_pb_divider _builder_version=”4.21.0″ _module_preset=”default” hover_enabled=”0″ sticky_enabled=”0″][\/et_pb_divider][\/et_pb_column][\/et_pb_row][\/et_pb_section]\n","protected":false},"excerpt":{"rendered":"

          Summer Created a Misleading Growth Surge It has been a hot, humid summer across much of the U.S., and one of the most common questions we\u2019ve received is some version of: \u201cWhy is my PGR program not working anymore?\u201d The evidence is usually sitting in the mower baskets. Bentgrass greens have continued to produce surprisingly […]<\/p>\n","protected":false},"author":3,"featured_media":102169,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"on","_et_pb_old_content":"","_et_gb_content_width":"","_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[5],"tags":[],"class_list":["post-102165","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog"],"jetpack_featured_media_url":"https:\/\/www.greenkeeperapp.com\/marketing\/wp-content\/uploads\/2026\/08\/ChatGPT-Image-Aug-25-2026-03_18_11-PM.png","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.greenkeeperapp.com\/marketing\/index.php\/wp-json\/wp\/v2\/posts\/102165"}],"collection":[{"href":"https:\/\/www.greenkeeperapp.com\/marketing\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.greenkeeperapp.com\/marketing\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.greenkeeperapp.com\/marketing\/index.php\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/www.greenkeeperapp.com\/marketing\/index.php\/wp-json\/wp\/v2\/comments?post=102165"}],"version-history":[{"count":7,"href":"https:\/\/www.greenkeeperapp.com\/marketing\/index.php\/wp-json\/wp\/v2\/posts\/102165\/revisions"}],"predecessor-version":[{"id":102187,"href":"https:\/\/www.greenkeeperapp.com\/marketing\/index.php\/wp-json\/wp\/v2\/posts\/102165\/revisions\/102187"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.greenkeeperapp.com\/marketing\/index.php\/wp-json\/wp\/v2\/media\/102169"}],"wp:attachment":[{"href":"https:\/\/www.greenkeeperapp.com\/marketing\/index.php\/wp-json\/wp\/v2\/media?parent=102165"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.greenkeeperapp.com\/marketing\/index.php\/wp-json\/wp\/v2\/categories?post=102165"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.greenkeeperapp.com\/marketing\/index.php\/wp-json\/wp\/v2\/tags?post=102165"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}