Released July 2, 2008

LINCOLN, Neb. — Weeds are the No. 1 problem when it comes to organic farming. To combat this, University of Nebraska-Lincoln researchers are studying weed control with a propane-induced flame.

It started with a custom-built propane flamer mounted on a four-wheeler. This is driven along field rows while emitting a flame that kills weeds. The flamer has four burners, positioned about 7 inches above the surface at a 30 degree angle to the soil.

Flaming weeds could become an alternative method for controlling weeds in organic field crops, said Stevan Knezevic, weeds scientist at the Haskell Agricultural Laboratory near Concord.

"It will allow organic producers to explore other options for weed control," Knezevic said.

Right now hand weeding and cultivation are the two most common weed control methods organic farmers use. Hand weeding has become cost prohibitive due to rising labor costs, while repeated cultivation increases soil erosion and emergence of new weeds. A few organic herbicides are approved for organic production, but they too are cost prohibitive.

With the increase in organic production and its demand from consumers, finding easier weed control methods can give organic producers another tool, he said.

Knezevic and Santiago Ulloa, UNL graduate research assistant, studied four crops – corn, sorghum, soybeans and sunflowers – and four weeds – barnyard grass, green foxtail, velvetleaf and redroot pigweed. Fields were irrigated and other volunteer weeds were controlled by hand weeding.

When weeds are flamed, the heat from the flame is transferred to the plant tissues. This increases the thermal energy of the plant cells and coagulates proteins if temperatures are above 122 degrees Fahrenheit. Exposing a plant to 212 degrees causes cell membranes to rupture, resulting in water loss and plant death.

Broadleaf weeds were more susceptible to flames than grasses, while corn and sorghum were less susceptible and soybean and sunflower were severely injured.

Flaming weeds in corn has the best potential, Knezevic said.

To perfect this weed control method, researchers are studying just the right dose of propane and pressure to control the weeds without damaging the crops.

Based on the first year of data, broadleaf weeds and broadleaf crops were more susceptible to flaming than grassy species. About 8.4 gallons of propane per acre was needed to obtain 80 percent control of velvetleaf and pigweed. Higher propane rates were needed to obtain the same level of control of barnyard grass and green foxtail at 14 days after treatment.

"Despite the fact that there was 80 percent control of grassy species at 14 days after treatment, there was no complete kill of the barnyard grass and green foxtail and plants were still growing several weeks after flaming," he said.

Right now, flaming has the best potential to control broadleaf weeds. Even though it did not completely kill barnyard grass and green foxtail, flaming still provides early season control – up to six weeks – by severely reducing growth and offsetting the weed's competition against the crop.

This research, conducted in 2007, has set a baseline of information on crop and weed tolerance to flaming and a dose response curve for propane. These trials will be repeated this year and in 2009.

Future research will study flaming in other grass-type crops and various broadleaf crops and weeds as well as further study crop tolerance to flaming.

Funding for this Agricultural Research Division research in the university's Institute of Agriculture and Natural Resources was provided from the Propane Education and Research Council and the Nebraska Propane Association.

--30--

http://ianrnews.unl.edu/static/0807021.shtml

Contacts: Stevan Knezevic, (402) 584-2808

Sandi Alswager Karstens, (402) 472-303