Golfdom, March 2018

TIMELY TURF ADVICE by Clark Throssell Ph D Clark Talks Turf PGR overregulation on greens collars Bill Kreuser Ph D is a turfgrass scientist at the University of Nebraska Lincoln where he conducts research on plant growth regulators PGRs turf growth and remote sensing You may reach Bill at wkreuser2@ unl edu for more information Q Describe the term overregulation as it pertains to PGRs Overregulation occurs when there is a large enough quantity of PGR in the turfgrass plant that the plant cant handle traffic and wear Simply put the turf is not growing fast enough to cope with stress Q What are the symptoms of overregulation on a green On greens segregation between annual bluegrass and creeping bentgrass will be pronounced Specifically annual bluegrass and ultradwarf bermudagrass becomes sunken and creeping bentgrass becomes bluer in color Individual segregates of creeping bentgrass can stand out and off types of bermudagrass greens will be obvious On annual bluegrass and creeping bentgrass collars the grass has a reddishbrown color and has poor traffic tolerance Q How does overregulation occur Overregulation can occur through a large single PGR application or when repeat applications are made too close together The intensity of suppression is rate dependent High application rates increase the amount of suppression and increase the risk of phytotoxicity Application rate has a much smaller impact on the duration of growth suppression Air temperature and mowing height and frequency affect the length of control Applying PGRs too frequently leads to an OVERREGULATION CAN OCCUR THROUGH A LARGE SINGLE PGR APPLICATION OR WHEN REPEAT APPLICATIONS ARE MADE TOO CLOSE TOGETHER accumulation of PGR within the plant because superintendents are applying a PGR faster than the plant breaks it down This increases the effective application rate and increases suppression Another common overregulation situation is applying PGRs on summer intervals during the cool spring and fall weather It also happens where different turf areas meet i e greens and collars Generally cool season collars are slower to break down PGRs than greens Many repeat PGR applications then can lead to overregulation on collars Our research plots showed we can cause severe collar decline simply by applying PGRs to collar height turf on greens intervals Q Do different PGRs have an additive effect on turf Yes PGRs work on the same biochemical pathway albeit at different points in the pathway but the impact of different PGRs is additive to the turfgrass If a superintendent wants to switch PGRs a different a i wait until the first PGR is exhausted before applying a different PGR Q What should superintendents do to minimize the problem if they notice overregulation on a collar First monitor PGR application intervals using GDD growing degree day models found at the GreenKeeper app greenkeeperapp com and adjust application intervals based on weather In areas where different turf species meet avoid PGR overspray or eliminate PGRs for collar applications This can be challenging because tank mixes typically contain other important fertilizer and control products I recommend GPS sprayers and stand alone PGR applications on greens to minimize this issue We are just beginning to explore the use of GA gibberellic acid applications to minimize overregulation impact Based on what we now know a single low rate GA application may help in some situations The downside of a GA application If its applied to locations where the turf is not overregulated the turf becomes etiolated and looks horrible Preventative options we are testing include a small reduction in collar mowing height increased nitrogen fertilization on collars and even washing foliarabsorbed PGRs off the leaves with a hose Q Is there anything else you would like to add Be constantly aware of the impact PGR applications are having on turfgrass growth Carefully monitor the volume of clippings produced from a green or two and determine if those greens are handling traffic as desired GreenKeeper can help monitor PGR performance and clipping yield production Adjust nitrogen and PGR applications as necessary to achieve healthy levels of growth Clark Throssell Ph D loves to talk turf Contact him at clarkthrossell@ bresnan net 42 Golfdom March 2018 Golfdom com