Figure 1. A four-row prototype flamer built by an IANR research team led by UNL professors Stevan Knezevic and George Gogos and tested in 2011. The researchers hold a patent for flaming equipment. (Photos by IANR Staff)	Figure 2. A three-row flamer mounted on an ATV is tested in the field. Tests were conducted in the evening to better observe flame shape as the flame hits the ground.

August 9, 2012

Weed control is the number one problem for organic farmers, who cannot use the chemical herbicides that conventional farmers can. Instead, organic producers must rely on alternative methods, including hand weeding and cultivation.

Knezevic and his team test the flamer in tall weeds. The height and growing stage of weeds and crops affect the duration and method of applying flame.

Increasing interest in organic food production has led to renewed interest in an alternative method for weed control, flame weeding. Flame weeding, which uses direct heat from a flame to kill weeds, has been used in agriculture since the 1950s, said Stevan Knezevic, extension weeds specialist at UNL’s Haskell Agricultural Laboratory near Concord. Knezevic has been researching flame weeding since 2006.

How Flame Weeding Works

In flame weeding, a propane-fueled torch shoots a flame at the targeted weeds. The flame can reach a temperature of up to 2500°F — much hotter than is required to denature plant proteins, Knezevic said. At 212° F water in the plant boils, expands, and breaks cell walls. As moisture leaks out from the plant, it wilts and eventually dies.

Flame weeding equipment varies in size. It can be as small as a handheld torch with a propane supply tank that a person straps on like a backpack, or as big as a commercial eight-row, tractor-pulled apparatus. In 2008, Knezevic teamed up with UNL mechanical engineering professor George Gogos to research and design better flame-weeding machinery. After building and testing a four-row prototype flamer, Knezevic and Gogos now hold a patent.

Pros and Cons of Flame Weeding

For organic producers, propane-fueled flame weeding is a useful addition to their weed control arsenal because it is cleared for organic use. Propane is clean burning, non-toxic, and will not contaminate groundwater. Also, the cost of flaming is relatively cheap compared to the cost of hand weeding. Propane for the flamer will range from $8 to $15 per acre.

Flame weeding, also known as flaming, can be used with conventional crops, organic crops, and in urban settings where herbicide use is undesirable, such as in parks. Some conventional farmers are considering flame weeding because heavy use of herbicides can lead to herbicide-resistant weeds, whereas flaming doesn’t, he added.

One drawback to flame weeding is that commercial flaming machinery is limited in size, Knezevic said, and not meant to be used as a standalone method for weed control.

Randy Fendrich, who farms organically near Abie and David City, has been involved in Knezevic and Gogos’s research. Fendrich said flaming has helped him control certain weeds more effectively by killing entire plants instead of just what’s above ground.

“With the flamer, we can get a total kill. With the rotary hoe and harrow, we’ll miss some of them and we won’t get a total kill,” he said.

Fendrich also uses hand weeding and a rotary hoe, harrow, and cultivator to control weeds in addition to flaming because different methods work better for different weeds. For example, he said he could use a rotary hoe to pull out grass that a flamer would burn but not kill.

Weed control also involves balancing the soil nutrients and getting the crop rotation right, said Mike Ostry, an organic farmer near Bruno. He has hosted test plots where Knezevic and Gogos conducted flaming research.

Research Helps Determine Flame Weeding Best Practices

The duration of heat applied to kill weeds varies with the kind of weed and crop. Crops are sensitive to heat and improper flaming could result in severe yield losses.

“It’s a very safe method if you know what you’re doing, but you can hurt your crop pretty badly too if you don’t know what you’re doing,” Knezevic said.

Knezevic, Gogos, and their team have conducted research on 20 weed species among seven agronomic crops: field corn, popcorn, sweet corn, sorghum, soybean, sunflower, and winter wheat. The researchers studied flaming of weeds at different stages of crop emergence, noting where growing points were on both crops and weeds.

Together with the Propane Education and Research Council, Knezevic, Gogos, and their research assistants are compiling their research results into a how-to manual on flaming equipment and best practices.

“We haven’t really used anybody else’s data. This is all home-grown,” Knezevic said.

The manual contains detailed instructions on setting and using flaming equipment, including calibrating propane pressure and speed to achieve the correct flame dosage, tolerance of weed species at different growth stages, and recommended growth stages for flame weeding in various crops.

Practice Makes Perfect

A manual like that would be very useful to producers, Ostry said. “We get so many different weeds that we need to control, and they need different timing and temperatures to kill them,” he said.

But gaining knowledge is not enough. Mastering proper flame weeding techniques, such as knowing how quickly to go so that the weeds are exposed to a specific duration of heat, requires practice. “You can go to seminars and see pictures but actually it’s a hands-on experience,” Ostry said.

Practice is also necessary so that flaming machinery can be operated safely. “I was scared of it at first because you have all this fire behind you roaring,” Fendrich said. “But after I ran the system a few days, I realized you just have to be careful when you run it and it’ll be OK.”

Learning More About Flame Weeding

Knezevic said the flame weeding manual is going through a review process and will be released sometime this year. Once approved, it will be available for download from the Propane Education and Research Council website for free.
Knezevic and Gogos also will be conducting a one-day flame weeding workshop on Aug. 15 at the Haskell Agricultural Laboratory near Concord. For more details, see the July 27 CropWatch story on the event.

Jaclyn Tan
IANR Student Newswriter