Heat tolerance of Kentucky bluegrass as affected by trinexapac-ethyl

Heat accumulation during storage of sod may reach lethal temperatures withi n 4 days, decreasing sod quality. Treatment with trinexapac-ethyl reduces h eat accumulation during sod storage. However, heat tolerance of grasses tre ated with trinexapac-ethyl has not been documented, Our objectives were to: 1) determine the lethal temperatures for Kentucky bluegrass (Poa pratensis L.); and 2) identify the effect of a single application of trinexapac-ethy l on heat tolerance. Experimental design was a randomized complete block wi th three replications and a two (trinesapac-ethyl vs. control)xtwo (cultiva rs) factorial arrangement of treatments. Ten days after chemical treatment, Kentucky bluegrass sprigs were exposed to heat stress for 4 days in a temp erature gradient block under low vapor pressure deficit. Treatment with tri nesapac-ethyl at 0.23 kg.ha(-1) reduced heat tolerance, Temperature needed to kill 50% of the population was 35.5 degreesC for treated vs. 36.1 degree sC for nontreated grass. Trinexapac-ethyl is in the same chemical family as the cyclohexanedione herbicides that interfere with lipid syntheses in gra sses. This may be a reason for the slight decrease in heat tolerance. The p ractical value of trinexapac-ethyl treatment in reducing heat accumulation during storage of sod may be partially negated by a decrease in heat tolera nce. Chemical name used: [(4-cyclopropyl-alpha -hydroxy- methylene)-3,5 -di oxocyclohexanecarboxylic acid methyl ester] (trinexapac-ethyl).