An initial patent for flame machinery for weed control was issued in 1852. In the 1930s, equipment and techniques were developed to allow use of vaporized fuel oil for flame cultivation in row crops. The introduction of the liquified petroleum gases butane and propane in 1945 significantly advanced flame capabilities, and in the 1950s through the early 1960s, flame cultivation was a popular weed control practice in cotton. Interest in flame cultivation in cotton declined with the development of effective residual herbicides, particularly trifluralin.

Several factors have revived interest in flame cultivation in cotton: a) need for control of hard-to-manage species such as morningglories, b) need for prevention or management of herbicide resistant weeds, and c) interest in non-pesticide weed control alternatives. Practically, flame cultivation is a supplemental tool and must be integrated with chemical and mechanical control efforts. Flame cultivation may substitute for postemergence directed and layby herbicide treatments and is compatible with mechanical cultivation.

The physiological basis for flame weed control involves high temperature injury to cambial cells of small weeds. Temperatures in excess of 130°F within the stem of target plants are necessary for effective control. Cotton with a stem diameter of 0.19 inch (or 3/16 inch) and in excess of 8 inches tall is tolerant of flame directed to the base of the plant.

Guidelines for equipment operation include: 1) tractor speeds of 3 to 6 mph to minimize cotton exposure time to flame to less than 0.15 second, 2) fuel pressure regulation of 30 to 50 psi to insure adequate coverage but not excessive heat penetration into the crop stem, 3) burners mounted 8 to 10 inches from the crop row and 6 to 10 inches above the crop at an angle of 30 to 45°, 4) initiating and/or repeating flame cultivation before weeds reach 3 inches tall but after cotton reaches 8 inches in height.

An optional water shield allows flaming of smaller cotton. A "shield" is achieved with a spray nozzle directing water parallel with and just above the flame. Spray volume and pressure of at least 7 gpa and 40 psi are needed to achieve adequate protection.

Flaming provides effective contact control of morningglories, perennial vines, prickly sida, cocklebur, pigweed, and most annual grasses. Species such as yellow and purple nutsedge, hemp sesbania, and spotted spurge are less sensitive to flaming. In addition to typical treatments directed to the crop drill, flame cultivation can also be used for elimination of row middle vegetation.

Fuel consumption for flame cultivation averages 4 to 6 gpa. Propane costs vary across locales, but average costs might be expected to be $0.50 to 0.70/gal, resulting in a cost of less than $4.50/acre. Because flame cultivation would provide a use of propane during periods of low demand, suppliers may be willing to negotiate on price due to potential for market expansion.

Flame cultivation is not without problems. Used alone, it will not provide adequate weed control. Timeliness is critical to insure effective kill of even small, susceptible weeds. Obviously, there is potential for crop injury if applications are too early or if burners are improperly aligned. In addition to potential personal injury to the operator, fire hazards in the crop field or border are a concern.

Flame cultivation could once again become a valuable tool for cotton producers. Prior research and experience demonstrate its effectiveness as an economical alternative weed control method. Additional work is needed to determine its efficacy on certain weeds such as tropic croton, bristly starbur, burgherkin, citron, and wild poinsettia.