What can you tell me about flame weeding as a method of weed control in organic crops?
Answer: Flame weeding is a non-chemical weed-control technique common among organic farmers. Flame weeding, also referred to as flame cultivation, often uses propane gas burners to produce a carefully controlled flame that briefly passes over weeds. The intense heat blanches the leaves, causing a disruption within the plant’s cell walls. Flamed weeds usually wilt and die anywhere from within a few minutes to a few days after flaming. One quick way to check to see if the plant foliage has been adequately flamed is to see if a thumb print is retained on the leaf when pressed between your thumb and finger.Weeds are most susceptible to flaming when they are one- to two-inch-tall seedlings. Broadleaf weeds are more susceptible to flaming than grasses as grasses develop a protective sheath by the time they are approximately one inch tall. Therefore, grasses may require a second flaming. Repeated flaming can also be used to suppress perennial weeds such as field bindweed. Flame weeding is commonly used in the stale seedbed method, which involves allowing weeds to grow in order to be killed by the flame (or other method). This method is usually repeated prior to planting a cash crop as another flaming may be used after planting and before germination of the cash crop. Flaming on dry, sunny days is recommended as any moisture can give the plants some resistance to the heat. For larger areas, working in sections can help establish effective fire breaks, particularly when flaming dried material, such as stubble, as it can ignite. Green plants usually do not ignite when treated with a flame. Most flame weeders are designed to not radiate large amounts of heat. Their purpose is to sear the leaves of plants (weeds) in order to change the protein structure of the plants. As a result, stress kills the weeds, not the torching of them. Due to the design and purpose of flame weeders, there is no soil disturbance and generally not enough heat is produced to penetrate the soil and effect soil life. As stated above, timing is everything. There are several different designs commercially available for tractor-mounted flame weeders. Some flame weeders burn propane in the gas state, while others burn gas in the liquid state. It is important to note that tractor-mounted tanks should be rated for “motor fuel” as they will be mobile and not stationary. Another design difference is whether the gas flows directly from the tank to the burners, or is distributed through a manifold first. In addition, the burners may be fixed or adjustable, with the latter offering the ability to adjust the position of the flame. Having individual shut-off valves for each burner provides flexibility in using a flame weeder so that the flames can be directed or broadcast over an area. Flame weeders are available with different BTU (British Thermal Unit) ratings. In addition to weed-control benefits, flame weeders can also be utilized for other applications. According to some resources, potato plants up to eight inches tall can be flamed to kill Colorado Potato Beetles, Leptinotarsa decemlineata, without causing undue damage to the potato plants. Flamers can also be used to incinerate fallen fruit and mulch.For more information on flame weeding, see ATTRA publication Flame Weeding For Vegetable Crops, available at https://attra.ncat.org/attra-pub/summaries/summary.php?pub=110.