Golfdom, October 2012

S PRACTICAL RESEARCH DIGEST FOR TURF MANAGERS P O A A N N U A C O N T R O L Tenacity A New Weapon in the Poa Annua Battle By Bruce Branham Ph D C ontrolling annual bluegrass Poa annua has been a challenge for turfgrass managers since we began managing it Finding herbicides that control annual bluegrass selectively has been difficult and only in the past decade have we been able to use products that can provide postemergent control of annual bluegrass reliably Velocity bispyribacsodium manufactured by Valent is one of the first herbicides to control annual bluegrass with postemergent applications safely and effectively Other herbicides have been used but the results were inconsistent or caused excessive injury or death to the desirable turf Its difficult to find selective herbicides to control annual bluegrass in Kentucky bluegrass Both species are from the same botanical genus and are presumed to be similar in growth and physiology Currently there are no herbicides labeled for the postemergent control of annual bluegrass in Kentucky bluegrass Tenacity mesotrione is a relatively new herbicide introduced in the market in 2008 by Syngenta Mesotrione has been used on corn for several years under the trade name Calisto This reduced risk herbicide is an analog of a natural product leptospermone which is produced by the bottlebrush plant Callistemon citrinus Mesotrione which represents a new class of herbicides known as HPPD inhibitors works by inhibiting the enzyme 4 hydroxyphenylpyruvate dioxygenase HPPD which blocks the pathway that produces plastoquinone and tocopherols antioxidants that reduce damaging oxygen radicals Without plastoquinone carotenoids which are critical for harvesting light and quenching the high energy states of chlorophyll cant be synthesized Without carotenoids radicals and reactive oxygen species damage the photosynthetic enzymes and membranes so that eventually all leaf pigments cant be produced Beaudegnies et al 2009 This causes the characteristic bleached tissue look in plants treated with HPPD herbicides and its common to all HPPD inhibitors Mesotrione selectivity derives from differential rates of metabolism in plants Tolerant plants degrade mesotrione rapidly susceptible plants have a slower rate of mesotrione metabolism We noticed that in the cooler temperatures of spring and fall mesotrione would cause bleaching of annual bluegrass During the sum Continued on page 34 OUR SPONSORS www andersonsinc com 800 537 3370 www fmc com 800 321 1FMC www turfgrasstrends com October 2012 TURFGRASS TRENDS 33