Flame weeding for vegetable crops
Flame weeding -a type of thermal weed control- was commonly used in row crops like cotton and sorghum from the late 1930s until the mid-1960s, when selective herbicides became widely available. In the 1980s and '90s, flame weeding made a rapid comeback as a non-chemical weed control technique, especially among organic farmers.
Flame weeding, also called flame cultivation, relies on propane gas burners to produce a carefully controlled and directed flame that briefly passes over the weeds. The intense heat sears the leaf, causing the cell sap to expand and disrupt cell walls. Foliage that retains a thumb print when pressure is applied between your thumb and finger has been adequately flamed. The flamed weeds soon wilt and die, usually in one to three days.
Weeds are most susceptible to flaming when they are seedlings, 1 or 2 inches tall. Broadleaf weeds are more susceptible to lethal flaming than grasses. Grasses develop a protective sheath by the time they are approximately 1 inch tall and may require a second flaming. Repeated flaming can likewise be used to suppress perennial weeds such as field bindweed.