Weed control by flaming and hot steam in apple orchards

Field experiments to investigate the efficacy of weed control by flaming, hot-steam and mulching on the natural weed flora at different developmental stages were conducted in apple orchards in Nova Scotia, Canada. The perennial weed most resistant to flaming was Malva neglecta, with no control at a total gas dose of 320 kg/ha. The effect of flaming on annual weeds depends mainly on the developmental stage of weed species and the propane dose required for the desired control level. To control annual weeds at later developmental stages (> 6 true leaves), single flame treatment with a propane dose of 54-40 kg/ha was not sufficient. For Chenopodium album three subsequent treatments were necessary for 95% control at a total propane dose of 162 kg per ha. For the flame control of Taraxacum officinalis the developmental stage is also crucial. If flame tolerant perennial weeds occurred in the orchard, only 76% weed reduction was achieved after four treatments and a total gas dose of 320 kg/ha. In an orchard with mainly annual weeds, three treatments and 162 kg/ha of propane controlled 95% of the weeds. The hot steam technology was not effective. An exposure time of 540 s at 150°C of the steam was not sufficient to control weeds. Mulching was a good alternative to reduce herbicide use, regardless of material used: coarse bark, saw-dust, hay.