Hot stuff

July 1, 2002 By    

Farmers who flame-broil the weeds infesting their fields and orchards are finding that this method is safer for the environment and at the same time more cost-effective than chemical defoliants and pesticides.

These propane-powered units don’t actually incinerate the targeted weed, but flame weeding does heat it up enough to strike a fatal blow as the device moves down the row.

“We’re just there long enough to singe it,” explains Tim Morse, marketing manager for Flame Engineering Inc. of LaCrosse, Kan. The company manufactures a line of flaming equipment for applications ranging from homeowner use to large agricultural operations.

With weed flaming, the weed is exposed to enough heat to vaporize the water within its cells, destroying its photosynthesis capabilities. As the flame moves down the row, staying at least two inches away from the crop, little smoke is seen because the weeds are green and propane is a clean-burning fuel. Shortly after flaming, the weed will wither and die, opening the crop to sunlight and growth.

A resurgence of weed flaming on U.S. farms could reopen agriculture market segments to propane use. Top: Flaming fields of alfalfa uses 20 to 30 gallons of fuel per acre. Above: Tractors flame corn rows at speeds of 3 to 5 mph.
A resurgence of weed flaming on U.S. farms could reopen agriculture market segments to propane use. Top: Flaming fields of alfalfa uses 20 to 30 gallons of fuel per acre. Above: Tractors flame corn rows at speeds of 3 to 5 mph.

According to the National Propane Gas Association and the Propane Education & Research Council, a propane flamer is cheaper for achieving the desired levels of control. It costs about $3.50 per acre per application, versus $15 to $18 when chemicals are applied. Money figures obviously will vary according to the price of propane – and the consumption rate will differ depending on the machine being used and the crop being treated. A standard row crop can be treated with five to 10 gallons of propane per acre, while alfalfa requires between 20 and 30 gallons per acre.

Flame cultivation also has been effective when used in conjunction with herbicides, particularly when dealing with species that are tolerant to a specific chemical product, according to Dr. Wayne A. LePori, a professor with the department of Biological and Agricultural Engineering at Texas A&M University.

With insects, the propane flaming approach can provide 70 percent to 90 percent control of wintering adult insects, compared with 25 percent to 50 percent provided by chemical pesticides.

Rainfall immediately following a chemical treatment can wash away any intended results, while flaming carries with it no such liability.

Vineyard and orchard flamers are used to control unwanted weeds and grasses without adverse effects on vines and trees, irrigation lines, sprinklers and protective vine covers. The devices use three to six gallons of fuel per acre.
Vineyard and orchard flamers are used to control unwanted weeds and grasses without adverse effects on vines and trees, irrigation lines, sprinklers and protective vine covers. The devices use three to six gallons of fuel per acre.

Another iron in the fire within this segment is a device being developed by Delta Liquid Energy of Paso Robles, Calif. in conjunction with Origin Energy of Australia. Called the Atarus Stinger, this piece of equipment uses super-heated steam to kill weeds. A propane-fired steam generator emits a plume hotter than 850 degrees Fahrenheit while moving along at 3 to 4 mph. When used in vineyards, the unit is able to direct the steam under the vines while sparing drip irrigation lines and other materials – such as mulch – that might be imperiled by standard flaming, according to Delta.

Designs are being contemplated to treat a number of different crops. A two-row vineyard unit consisting of four steam generators costs about $25,000.

Hot stuff

Reams of technical, complex treatises and academic papers have been prepared on the subject of flame cultivation. A propane dealer wanting to enter this field would be well-advised to seek the necessary education.

Flaming standards vary with the crop being treated, soil type, temperature, depth of plantings, plant growth and even the size of the tines on raking equipment. Speed, torch angle and fuel pressure are among other factors.

For example, Morse at Flame Engineering stresses that a propane tank with a liquid withdrawal valve is required for his company’s equipment. It should be top-mounted with a tube that reaches close to the bottom of the tank-the tube should not touch the tank’s bottom. A bottom withdrawal valve should not be used because debris can enter the system and cause major problems.

A study by Dr. Dudley Smith, a professor with the Department of Soil and Crop Sciences at Texas A&M University, reveals that mainstream large-scale commercial farmers cited two main reservations about flaming: They feel that applying either liquid or granular herbicides is simply an easier task to accomplish, and the average 4 mph speed strikes them as being too slow for the amount of ground they must cover.

Flames from the staggered torches are directed under the crop leaves and through the crop row, destroying insects, weeds and grasses.
Flames from the staggered torches are directed under the crop leaves and through the crop row, destroying insects, weeds and grasses.

Another concern is that many of the folks most familiar with flame cultivation from the old days are retiring.

“Some growers cited lack of technical support (such as that provided by chemical suppliers) as a major need, particularly on equipment setup, burner adjustment and general operation for weed control,” Smith notes.

One marketing plus is that flaming technology lights the fire of many organic farmers, who are intent on controlling weeds and pests without using chemicals.

Charlie Lupher of Dream Catcher Farms in McDade, Texas, organically grows 10 to 15 different vegetables on his 40-acre spread. The commercial operation is profitable, but Lupher laments the weeds that continue to crop up. He welcomes Smith’s interest.

“Like most organic growers, Mr. Lupher was open to trying new practices and investing in the necessary equipment-but technical service and some field support in setup and operation would be a key for LP marketing success,” Smith reports.

Back to the future

Flame cultivation dates back to 1938, when Alabama farmer Price McLemore discovered that a kerosene flame could tackle the weeds afflicting his cotton and corn. His crude unit was pressurized by a bicycle tire pump, so it was rather inconvenient to drive through a farm field while simultaneously hand-pumping this bicycle pump. Laughter ensued, but an idea was born.

In 1942 propane flaming was applied to sugar cane at Louisiana State University. In 1943 came cotton, and in 1944 corn and soybeans were added to the mix. According to Morse, there were at least 1,000 flame cultivators at work in the cotton fields of the Mississippi Delta by 1946. The notion achieved continued acceptance as wet weather and soggy fields would render conventional cultivation impossible.

By 1960 an estimated 15,000 flaming units were in the fields, mostly used with cotton. Some also were being applied to corn and soybeans, and interest was growing for alfalfa and mint plants.

“In the years that followed, research proved that flame cultivation can be used on 30 to 40 different crops with good results,” notes Morse.

“Although the majority of the research has been done with corn, cotton and soybeans, many other crops such as milo , garlic, blueberries, strawberries, radish, lettuce, potatoes, asparagus, grapes, fruit trees and the Australian tea tree all have been successfully flame cultivated.”

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