Bolting Control by Ethephon in Fall-planted, Short-day Onions1

Abstract Fall and late-winter treatments of (2-chloroethyl)phosphonic acid (ethephon) at 2500 or 5000 ppm reduced bolting of fall-planted, short-day cultivars of onion ( Allium cepa L.). Ethephon inhibited plant growth and reduced bulb size. Ethephon reduced yields when bolting in control plots was low or when cool spring weather restricted growth. With warm spring weather and 18% bolting in control plots, ethephon reduced bolting to 3% with no effect on yield. Ethephon caused some winter plant loss in 1 of the 3 years. Loss was greatest when higher rates of ethephon were applied in the fall to very young plants.