Propane flaming could be an effective alternative tool for weed control in organic cropping systems. However, response of major weeds to broadcast flaming must be determined to optimize its proper use. Therefore, field experiments were conducted at the Haskell Agricultural Laboratory, Concord, NE in 2007 and 2008 using six propane doses and four weed species, including green foxtail, yellow foxtail, redroot pigweed, and common waterhemp. Our objective was to describe dose–response curves for weed control with propane. Propane flaming response was evaluated at three different growth stages for each weed species. The propane doses were 0, 12, 31, 50, 68, and 87 kg ha⁻¹. Flaming treatments were applied utilizing a custom-built flamer mounted on a four-wheeler (all-terrain vehicle) moving at a constant speed of 6.4 km h⁻¹. The response of the weed species to propane flaming was evaluated in terms of visual ratings of weed control and dry matter recorded at 14 d after treatment. Weed species response to propane doses were described by log-logistic models relating propane dose to visual ratings or plant dry matter. Overall, response of the weed species to propane flaming varied among species, growth stages, and propane dose. In general, foxtail species were more tolerant than pigweed species. For example, about 85 and 86 kg ha⁻¹ were the calculated doses needed for 90% dry matter reduction in five-leaf green foxtail and four-leaf yellow foxtail compared with significantly lower doses of 68 and 46 kg ha⁻¹ of propane for five-leaf redroot pigweed and common waterhemp, respectively. About 90% dry matter reduction in pigweed species was achieved with propane dose ranging from 40 to 80 kg ha⁻¹, depending on the growth stage when flaming was conducted. A similar dose of 40 to 60 kg ha⁻¹ provided 80% reduction in dry matter for both foxtail species when flaming was done at their vegetative growth stage. However, none of the doses we tested could provide 90% dry matter reduction in foxtail species at flowering stage. It is important to note that foxtail species started regrowing 2 to 3 wk after flaming. Broadcast flaming has potential for control or suppression of weeds in organic farming.

Nomenclature: Redroot pigweed, Amaranthus retroflexus L.; common waterhemp, Amaranthus rudis Sauer; green foxtail, Setaria viridis (L.) Beauv.; yellow foxtail, Setaria pumila (Poir.) Roemer and J. A. Schultes.