Propane flaming is a fairly effective pest control method for alfalfa growers, but herbicides and insecticides work better, says Steve Orloff.

The Siskiyou County, CA, farm advisor compared flaming and herbicides in an early spring weed control study. He used four treatments in large strips across an alfalfa field: An untreated control, a combination of Sencor and Gramoxone, and flaming at 11 or 22 gallons of propane/acre.

“The more propane we used, the hotter the fire became,” Orloff explains.

The chemical treatment controlled nearly 100% of shepherds purse, tansy mustard and Kentucky bluegrass, and flaming at the high propane rate gave 76%, 75% and 46% control, respectively, of those weeds. Flaming at the low rate controlled about 50% of the weeds.

“Flaming is much less effective on perennial weeds than on annual broadleaf weeds,” says Orloff.

Proper timing is critical for optimizing flaming results, he says.

“It should be done just as the alfalfa is breaking dormancy. If you do it before weed emergence, you may control all of the emerged weeds, but you'll get subsequent emergence after you burn. But, if you wait too late, the weeds will be too big to control with flaming.”

Flaming also reduced alfalfa weevil larvae numbers by about 50%. Weevils deposit their eggs in alfalfa stems. So burning the stems destroys weevil larvae and eggs, says Orloff.

It also may delay reinfestation.

“After you burn, the whole field looks charred, so it may be an inhospitable environment for weevils that are migrating in. They would rather go somewhere else.”

Flaming has been around for decades, but is enjoying a resurgence in some areas, with several equipment companies selling new models. Orloff thinks it may be best-suited for organic growers.

“They represent a small portion of alfalfa growers, but their numbers are growing, thanks to increased demand for organically produced milk and cheese,” he says.