Impact of selective flame weeding on onion yield, pungency, flavonoid concentration, and weeds

Field experiments were conducted to evaluate the effects of multiple selective flame weeding treatments on onion (Allium cepa L.). Onions were flamed between one and six times over the course of the season with a high (72 kg propane ha−1) or low (45 kg propane ha−1) propane dose. In each treatment, one subplot was hand-weeded in addition to flame treatment to remove differential weed effects, while the other received only the prescribed flame weeding regimen as weed control. Overall, control of broadleaf weeds was better than that of grass species. Broadleaf weed density and shoot mass were reduced as propane dose and the number of flame treatments increased. Grass density was reduced by 50% in all flamed treatments compared to the non-treated control, but no differences between flamed treatments were observed. Effects of flame treatments on grass shoot mass were minimal. Among weed-free treatments, onion was able to tolerate up to six flame treatments at either dose without a loss of yield. Treatments that received only flame weeding as weed control had total onion yields 37 and 80% of the weed-free flamed treatments in 2006 and 2007, respectively. Flame weeding treatments had little effect on the time to reach maturity, onion pungency, or quercetin concentration.

► Dicot weeds were better controlled by flame weeding treatments than monocot weeds.
► In weed-free conditions, onion tolerated up to six flame weeding treatments without loss of yield.
► Flame weeding treatments alone could not control weeds sufficiently to avoid yield loss.
► Effects of flame weeding on onion pungency or quercetin concentration were limited.