| Flame weeding is a thermal weed control method that controls weeds through the application of extremely high temperatures. Field experiments were conducted from 2005 to 2007 to determine weed and crop tolerance to flame weeding and to investigate effects on plant development, crop yield, and crop quality. Dose-response curves were constructed for weeds common to horticultural fields in Quebec. Flame weeding was more effective in controlling dicot weeds than monocot weeds. Flame doses that reduced common lambsquarters density by 95% (LD95) ranged from 0.83 to 2.85 kg propane km-1 for plants at the cotyledon through the 6-leaf growth stage. LD95 values for redroot pigweed ranged from 1.19 to 2.72 kg propane km-1 for plants at the cotyledon through the 4-leaf growth stage. In shepherd's-purse, LD95 values for weeds at the cotyledon and the 2- to 5-leaf growth stage were 1.15 and 2.78 kg propane km-1, respectively. Control of monocot weeds was poor, with survival greater than 50% for all flame doses evaluated. Onion and broccoli were tolerant of a single flame weeding treatment, with yield losses observed only when flamed within 20 days after transplantation (DAT). Among weed-free treatments, onion was able to withstand up to six flame treatments without any detectable loss in yield. However, flame treatments alone were not able to provide sufficient weed control to maintain yields. Flame weeding had minimal effects on time to reach maturity, leaf and bulb development, pungency or quercetin concentration in onion. Broccoli tolerated up to four flame treatments in weed-free plots without yield reductions. Flame-only treatments had lower yields than the flamed, weed-free treatments in one of two years. Flame treatments had limited effects on the number of days to maturity, leaf development, and glucoraphanin concentration in broccoli. Yield losses in spinach and beets were observed when flamed at both the 4- and 6-leaf growth stages; however, no adverse yield effects were observed when spinach or beets were flamed preemergence. Selective flame weeding is a valuable weed control option and has the potential to reduce the amount of costly hand-weeding employed in organic production for many flame-tolerant crops. |
