Scorched Earth Attack on Resistant Weeds

Harry Stephens is scorching earth to save money and boost yield on his farmland. The Phillips County, Ark., producer spent several hundred dollars to treat 3,000 acres of soybeans with innovative weed prevention using just a few bars of iron, plywood and propane bottles. Narrow windrow burning, a weed control method pioneered in Australia, has arrived on U.S. ground and may offer producers a reduction in soil seed bank population and a drop in herbicide expense.

Palmer amaranth waits to storm Stephens' 3,000 acres of soybeans acres each year, bursting from the ground in early spring.

“We get some pigweed as big around as a man’s leg,” Stephens says.

Two years earlier, a miscommunication at planting left 35 acres with no pre-emerge herbicide applied, and the oversight cost Stephens $100 per acre in subsequent ineffective treatments. Once trailing, there is no way to catch up with the speed and ferocity of Palmer. Get four or five days behind Palmer, and the chemical solution is over, he says.

“Pigweed packs an incredible financial punch in this farming area,” adds Robert Goodson, Phillips Co. (Ark.) Extension agent. “I know some farmers spend $80 per acre just in herbicide, before application costs or anything else. That’s extreme, but that’s what some folks have to pay. We pay attention to anything that helps reduce pigweed seed.”

After billions of dollars spent in herbicides every crop season, combines cut crops and weeds as a matched pair at harvest, scattering trillions of seeds back into fields to choke out subsequent crops. It’s a maddening cycle as weed history annually repeats and the soil seed bank gets fat on a full larder.

Searching for more weapons in the resistant weed war, Stephens heard about the narrow windrow pioneering efforts of Jason Norsworthy, weed scientist with the University of Arkansas, who first observed the technique in Australia as part of the Harvest Weed Seed Control (HWSC) program, developed by University of Western Australia weed scientists Michael Walsh and Stephen Powles.

“My expenses fighting pigweed get bigger every year, and narrow windrow burning is a promising way to fight weed seed,” Stephens says.

A chute attached to a combine funnels trash into a 30”-wide windrow. The concentrated biomass builds heat slowly as the burn degrades weed seed to ash, rather than allowing it to hide in the seed bank and rage across fields again. Temperatures in the windrow often exceed 450 F for several minutes, according to Norsworthy.

“Narrow-windrow burning destroys all weed seed within the chaff,” he says. “It is a highly effective means of managing the soil seed bank, especially resistant pigweed.”

Norsworthy has tested narrow windrow burning in fields infested with glyphosate-resistant Palmer amaranth. At one location, he switched from Roundup Ready soybeans to LibertyLink soybeans, and supplemented the change with narrow windrow burning. Over a three-year span, the soil seed bank dropped to a near-zero level.

“I’m talking about a field you couldn’t even put a combine in when we started three years earlier,” he says. “We had an effective herbicide program backed up with narrow windrow burning.”

The potential of a simple capture, burn and kill approach to weed seed caught Stephens’ attention, so he next visited Crittenden Co. (Ark.) Extension agent Russ Parker to get a bare-bones look at a windrow chute. Measurements in hand, Stephens took the specs to his sons, Kimbrough and Harry, Jr., who built two chutes in a single afternoon with a few bars of 20” metal and a sheet of plywood.

“The first one took a little while, but the second only took an hour to build,” Kimbrough says. “The whole setup cost a few hundred dollars. All I had to do was take the spreader bars off the combines.”

During cutting, the chutes don’t impede combine speed or performance. After combining, Stephens drives along the windrows in a truck with a propane torch on a trigger, or Kimbrough and Harry, Jr. ride the windrows on four-wheelers, with mounted propane torches wide open.

“We’ve done it several ways,” Kimbrough says. “Sometimes we may light each end of the row, leave it, and then come back a few days later and clean up with four-wheelers.”

The smoldering heat last for days, turning the biomass to a blanket of ash. At first glance, the result is a series of long, black stripes painted over 3,000 acres. In practice, the payoff is a direct assault on the motherlode source of weed seed. The narrow windrow method is far less intense than a corn or wheat field burn, which moves too quickly to kill weed seed in significant numbers. Stephens says the windrow burns are contained.

“One year, I set fire to the corner of a 90-acre wheat field with no wind," he says. "I went to the other end to burn, and I swear the wind was blowing 50 mph. Every farmer knows stories about field fires and burned pickups.”

Goodson recently analyzed a single Palmer specimen from Stephens’ ground and estimates it contained approximately 1.8 million seeds, an astounding amount of resupply for the seed bank. Goodson spends up to 60% of his time fighting Palmer in Phillips County and believes narrow windrow burning may become common practice on many farms.

“Reducing the seed bank is equivalent to saving money,” he says. “Why not spend just several hundred dollars to treat 3,000 acres with the windrow technique?”

“Just look at my expenses for herbicides, tillage and low prices for rotation crops,” Stephens echoes. “I think I can get my money’s worth from narrow windrow burning. We’ll spend more on propane than on chute material.”

After harvest, Goodson flaged and recorded the locations of particularly heavy 2016 Palmer infestations. He’ll use those test point locations during the 2017 and 2018 crop seasons as a gauge to measure the level of weed reduction. Resistant Italian ryegrass is also a mounting problem on the Stephens’ operation, and Goodson predicts windrow burning will help with ryegrass issues.

“This is about long-term reduction of the seed bank, complementary to a herbicide program,” Goodson notes.

Every year during harvest, combines chew through weeds and cast billions of seeds across U.S. farmland. It’s a devil’s bargain as crops come in, weed seed is scattered, and a herbicide battle rages once again. The logic of allowing billions of weed seeds to mix with soil after harvest is turned upright by narrow windrow burning, and Stephens is hoping for strong results.

“I’m doing this to save dollars and increase yield over time," he says.

“Whenever I drive to states in the north, the further I go the less pigweed I see. Those farmers may soon be in a position to consider windrow burning because they’re only a decade behind us,” he says. “I’d do anything to get back those 10 years of weed resistance.”