Flame weeding seen as alternative to herbicide control
Stevan Knezevic, University of Nebraska-Lincoln professor of agronomy and horticulture, weed science, has been working with U.S. propane officials to develop flaming equipment, techniques and guidelines for farmers who are looking for an alternative to herbicide weed control programs. (Loretta Sorensen/Midwest Producer)
September 04, 2013 9:55 am • By Loretta Sorensen, Midwest Producer
Kansas farmer Ralph Pivonka got the attention of his neighbors in 1959 when he used a torch to kill weeds in his fence line. His innovative approach to weed control led to development of commercial “flamers,” but the introduction of herbicide control that occurred about the same time took the heat out of Pivonka’s initial notoriety.
Now, with a growing need for alternative weed control methods for organic farmers and herbicide resistant weeds, flaming is once again coming to the forefront of integrated weed management.
Since 2006, Stevan Knezevic, University of Nebraska-Lincoln professor of agronomy and horticulture, weed science, has headed up a flame weeding team to help develop effective flame weeding equipment and methods. A recent daylong flaming workshop allowed interested farmers to learn more about flaming tools and techniques.
“Flame weeding could be an alternative weed control method,” Knezevic said. “During the flaming process, heat of about 2,000 degrees Fahrenheit is transferred to plant tissue, which causes water inside plant cells to boil and rupture, killing the plant.”
Flame weeding, compared with use of chemical herbicides in conventional crop systems, leaves no chemical residue on or in plants, soil, air or water. The method doesn’t cause any drift hazards and plants are not able to develop resistance to the process.
“One drawback is that most flame weeding systems are designed to treat between four and eight rows at a time,” Knezevic said. “They’re much smaller than chemical sprayers, so the flame weeding process is slow in comparison with chemical treatment.”
In contrast to cultivation, flame weeding doesn’t bring new weed seeds to the soil surface or disturb soil structure, which can lead to soil erosion. Flame weeding can be used in wet soil conditions.
For organic farmers who may use hand weeding, flaming reduces the cost of hand weeding and labor involved in organizing weeding crews.
“Flame weeding does have some disadvantages,” Knezevic said. “It can create a fire hazard in a field with heavy crop residue. There’s also potential to injure healthy crops in the process of killing weeds. That’s why it’s so important to properly schedule flame weeding to ensure safety of crops, operators and equipment.”
Propane-fueled weed equipment does produce some combustion byproducts. However, the byproducts emit 19 percent fewer greenhouse gases than diesel and 18 percent fewer greenhouse gas emissions than gasoline per unit of energy (assuming 100 percent combustion).
Plant cell content is 95 percent water. Propane-fueled burners can generate combustion temperatures as high as 3,400 degrees (1,900 degrees Celsius). The heat causes plant cells to rupture, which rapidly dries out affected plant tissue. Direct heat injury also causes cell proteins to denature, which means plant cells no longer function.
Interestingly, weeds subjected to flaming don’t always readily appear to have been affected by the process.
“A simple fingerprint test a few minutes after treatment provides an assessment of flame weeding’s effectiveness,” Knezevic said. “Place a treated weed leaf between your thumb and index finger. If a darkened impression is visible after firmly pressing on the leaf surface, that’s evidence of loss of internal pressure within the leaf due to water leakage from ruptured cell walls.”
It’s critical to use flame weeding at the proper crop grow stage. All agronomic crops are sensitive to heat. Flaming at the improper growth stage could result in severe yield losses.
“Grass-type crops such as field corn, popcorn, sweet corn and sorghum are more tolerant to propane-fueled post-emergence flame weeding than broadleaf crops, such as soybean and sunflower,” Knezevic said. “Post-emergence flame weeding isn’t recommended in winter wheat due to high injury level and unacceptable yield loss.”
Banded flame weeding torch configuration, which positions torches at least 6 inches from the crop row, is used to flame beneath the crop canopy. This approach protects the growing point of the crop during flame weeding, reducing potential for crop damage.
“Custom-designed hoods further minimize crop damage,” Knezevic said. “Banded flame weeding allows for treatment at a greater span of growth stages than non-selective broadcast flame weeding directly over the crop row.”
Flame weeding equipment design is still underway. However, a number of flame weeding systems are commercially available. Options range from handheld systems that can be used to control weeds in residential gardens to multi-row, tractor-pulled systems for use on large farms.
“Many farmers and mechanics choose to design custom flame weeding systems that meet their economic and crop configuration requirements,” Knezevic said.
The Propane Education and Research Council (PERC) developed a flaming guidelines manual, “Propane-Fueled Flame Weeding in Corn, Soybean, and Sunflower,” to aid farmers in developing a flame weeding strategy. The manual is available for download at http://agpropane.com/propane-safety-on-the-farm/service-manuals-and-training-guides/.
Knezevic noted that flaming is one of the tools farmers can use to effectively manage weeds.
“Integrated weed management includes selection of well adapted crop varieties and hybrids, appropriate planting patterns and optimal plant density,” he said. “You also have to implement precise timing, strategic placement and appropriate quality of nutrient application. In addition to flaming, alternative weed control includes steaming, infrared radiation and sand blasting.”
Genetically modified crops, used widely in North American agronomic cropping systems, rely heavily on use of herbicides, especially glyphosate.
“Repeated use of chemicals has potential to increase the number of herbicide-resistant weeds, increase herbicide costs and contaminate ground water,” Knezevic said. “Flaming is one alternative tool for growers seeking effective weed control.”