Flaming as a Method of Weed Control in Organic Farming Systems (E3038)
Using fire to control weeds in organic farming systems shows promise for reducing weed populations without herbicides.
Using fire to control weeds in organic farming systems shows promise for reducing weed populations without herbicides. A carefully directed flame fueled by natural gas or liquid propane (LP) increases the temperature within the weed, causing cells to rupture and effectively killing weeds while doing little damage to the crop (Fig. 1). Flaming disrupts weed growth through heat, so it is important to flame when the plants are dry and wind speed and direction are favorable. Both moisture and wind can lower the heat from the flame, reducing the effectiveness of the flaming application (Mutch et al., 2005).
Weeds are most susceptible to flame heat when they are 1 to 2 inches tall or in the three- to five-leaf stage (Sullivan, 2001). Broadleaf weeds are more susceptible to flaming than grasses such as foxtail.
Some farmers have found that flaming controls certain weeds (lambsquarters and pigweed, for example) better than others (mustards or common ragweed) (Mutch et al., 2005). Flaming is more effective in a crop such as corn, where the growing point is below the soil surface, than in crops such as soybeans, where the growing point is aboveground. The authors of this bulletin do not recommend using flaming to control weeds in soybeans.
Exposing a weed seedling to flame for 1/10 of a second (Row Crop, 2007) is usually enough to ensure control, although this may vary with weed type and size (Fig. 2). Smaller, sensitive plants are more susceptible to heat than larger, more mature plants. Applying the flame when the crop plants are larger than the weeds provides for optimal control. After an effective flame application, weed leaves look dull, and it is easy to press a visible fingerprint onto the leaf surface.