Ethephon Absorption and Transport Associated with Annual Bluegrass Inflorescence Suppression

ABSTRACT Ethephon suppresses annual bluegrass (Poa annua L.) inflorescence, but physiological effects attributed to efficacy have received limited investigation. Experiments were conducted to evaluate application placement, absorption, distribution, and metabolism of ethephon associated with inflorescence suppression in annual bluegrass. Ethephon applications to the antepenultimate leaf reduced inflorescence length 38 to 63% from the nontreated, while applications to the flag leaf reduced length 67 to 93% from 7 to 28 d after treatment. Annual bluegrass treated with 14C‐ethephon at the flag leaf distributed ~7X more radioactivity to the inflorescence than applications to the antepenultimate leaf and ~2X more 14C into nontreated shoots after 72 h. Radioactivity distribution to roots was minimal (≤2%) for both application placements. Annual bluegrass reached 50% foliar absorption of 14C‐ethephon at 13 and 17 h after treatment to the antepenultimate and flag leaf, respectively. Annual bluegrass metabolized 14C‐ethephon after 1 d to a nonpolar metabolite in the flag leaf, but a different metabolite accounted for ≥88% of 14C recovered after 7 d. Results suggest ethephon absorption and transport from the flag leaf contributes to annual bluegrass inflorescence suppression more than lower leaves, while transport from the flag leaf is likely in the form of a metabolite.