Organic Broadcaster

Proof Positive – Research highlights best practices for propane-fueled flame weeding

By Stevan Z. Knezevic, Chris Bruening, and George Gogos, University of Nebraska

Flame weeding has received renewed interest for its potential in not only organic, but also conventional cropping systems, especially in those fields where there is an increase in herbicide-resistant weeds.

Flame weeding controls weeds by heating plant tissue rather than burning it. Propane burners can generate combustion temperatures of over 2000 degrees F, which rapidly raises the temperature of exposed plant tissues. The resulting thermal shock to the plant tissues boils water molecules inside the cell and breaks up proteins, especially in the cell wall. The expanding water generates pressure that ultimately ruptures the cell wall, thereby dehydrating the plants through cell leakage. Eventually the plants die or their competitive ability is drastically reduced.

Flaming provides multiple advantages, including the fact that it:

(1) leaves no chemical residues in plants, soil, air or water;

(2) does not produce chemical drift hazards or herbicide carry-over to the next season;

(3) can control herbicide-tolerant or resistant weeds;

(4) reduces the need for repeated cultivation that promotes the risk of new weed flushes or increased soil erosion:

(5) is less costly than hand weeding, thus providing direct economic savings.

At the University of Nebraska, we have con­ducted a series of over 40 studies from 2008 to 2012 that resulted in many journal and proceeding articles about crop tolerance to heat and weed control with flame weeding in field corn, popcorn, sweet corn, sunflower, soybean, sorghum and winter wheat. In these studies, we determined that the propane doses of 10 to 12 GPA (gallons per acre) were highly effective in controlling many broadleaf weeds at early growth stages (up to 10” tall), providing over 90% control of major species: velvetleaf, ivyleaf morningglory, redroot pigweed, common waterhemp, lambsquarters, field bindweed, kochia, and Venice mallow. The same dose of propane also provided 80% control of several grass species, including barnyardgrass, green foxtail, and yellow foxtail. Control of the above weeds can be done prior to crop planting, as well as before and after crop emergence.

We also determined the tolerance level of major crops to propane flaming. The most tolerant crops are the grassy type crops such as field corn, popcorn, sweet corn, and sorghum, which can be safely flamed from VE (emergence) to V10 (10-leaf) growth stages, with a maximum of two post-emergence flaming operations per season. Soybean is tolerant to flaming only at the VE–VC stages (emergence-unfolded cotyledon) and after the V4 (4 trifoliate) growth stages. Sunflower is tolerant to flaming only at the VE–VC stage (emergence-cotyledon) and after the V8 (8 leaf) growth stage. Flam­ing in wheat is recommended only before crop emergence.

From an economic standpoint, the cost of a sin­gle flaming operation applied broadcast below crop canopy could be $12-15 per acre, without taking into account the costs of the equipment and labor [current price of propane ($1.20/ gallon) x 10 or 12 GPA]. Banded application (6 inches on either side of crop row) of flaming can cost $5-8 per acre due to lower propane use rates (4-6 gallons) per acre. Flaming can be utilized also as part of an integrated pest management program not only for weeds, but also for insect control in agronomic crops.

We have compiled results from this research into a training manual that describes the proper use of propane-fueled flaming as a weed control tool in major agronomic crops. The flame weeding manual contains 32 pages of text and color pictures. The pictures provide visuals of crop growth stages when flaming can be conducted safely without having side-effects on crop yield. Pictures of weeds provide visuals of appropriate growth stages when weeds need to be flamed to achieve good weed control. The manual is available as a free PDF download at service-manuals-and-training-guides.

For additional information on flame weeding, contact Dr. Steven Knezevic (402-584-3808),

January | February 2014

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