Annual bluegrass (Poa annua) is the most common weed found in creeping bentgrass putting greens.  Attempts to remove annual bluegrass from putting greens usually prove futile, and thus the weed is generally accepted as part of the turf sward.  A major component of annual bluegrass maintenance is seedhead suppression.  Annual bluegrass seedheads generally occur in the spring, but sporadic seedheads may be found any time in winter.  For seedhead suppression, applications of mefluidide + foliar iron or ethephon + trinexapac-ethyl are commonly applied at 50 growing degree days at base 50 (GDD₅₀).  Seedhead suppression from these applications is often inconsistent and additional applications may lead to turf injury.  Given annual bluegrass plasticity and variations in seedhead initiation, the objectives of this study were to determine if early-winter applications of ethephon applied before a 50 GDD₅₀ initiated spring program would improve annual bluegrass seedhead suppression. 

Two trials were conducted on creeping bentgrass putting greens mowed at 3mm at the Virginia Tech Golf Course in Blacksburg, VA and the Spotswood Country Club in Harrisonburg, VA.  Treatments consisted of a base program of ethephon at 3.8 kg ai ha^-1 + trinexapac-ethyl at 0.048 kg ai ha^-1 applied first at 50 GDD₅₀ and again 4 WAIT.  This basic program was augmented to form the following treatments: 1) No early treatment, 2) ethephon at 3.8 kg ai ha^-1 in January, 3) ethephon at 3.8 kg ai ha^-1 in February, or 4) ethephon at 3.8 kg ai ha^-1 in March.  Treatments 5 and 6 included a comparison of mefluidide at 0.007 kg ai ha^-1 + foliar iron applied at 50 GDD₅₀ and again 4 WAIT, and a nontreated control.  On April 6, at the Virginia Tech Golf Course, the nontreated plots averaged 66% seedhead coverage.  Ethephon + trinexapac-ethyl initiated at 50 GDD₅₀ averaged 45% coverage, and early treatments of ethephon initiated in January, February, and March averaged 6, 10, and 25% coverage, respectively.  Mefluidide + foliar iron averaged 48% seedhead coverage.  Similar trends were seen at Spotswood Country Club on April 26^th.  Ethephon early treatments initiated in January, February, and March averaged at 7, 6, and 18% coverage, respectively.  Ethephon + trinexapac initiated at 50 GDD₅₀ averaged 58% coverage, and mefluidide + foliar iron averaged 20% coverage with 10% turf injury.  The nontreated plots averaged 91% seedhead coverage.  These data suggest that January or February applications of ethephon can significantly improve seedhead suppression when applied with a 50 GDD₅₀ ethephon + trinexapac-ethyl program.