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New Tools in Resistant Weed Fight

08:10AM Dec 06, 2014

Harvest weed seed control measures, such as the Harrington Seed Destructor, team up

Every year at harvest, combines chew through weeds and spread billions of seeds across farmland. It’s a time-honored devil’s bargain: Crops come in, weed seed is scattered and farmers prepare for another fight the following spring. However, the logic of allowing billions of weed seeds to mix with soil after harvest is being turned upright by new non-chemical techniques and technology—harvest weed seed control (HWSC).

HWSC has proven highly efficient in Australia, where resistant weed experts Michael Walsh and Stephen Powles pioneered the system. HWSC relies on several control strategies, including chaff carts, narrow windrow burning, a bale-direct system and the Harrington Seed Destructor (HSD). Each technique captures or destroys weed seed and ensures it doesn’t return to the soil bank.

Chaff carts are common in Australia. During harvest, the weed seed bearing chaff residue is directed into a cart attached to the back of a combine. The chaff, including weed seeds, is then burned or used for livestock feed. 

In 2013, Jason Norsworthy, weed scientist, University of Arkansas, built a chaff cart to test. “You dump the material in the field and burn heaps of residue containing seeds. The carts are generally 13' tall by 8' wide and hold a tremendous amount of material.”

Narrow windrow burning is used on 30% of crop production in Australia. During harvest, the chaff and straw residue are funneled into a narrow windrow by a chute attached to the combine. The windrows are then burned to destroy the weed seeds. 

“We’ve looked at narrow windrow burning,” Norsworthy says. “For $200, we can build a chute designed for the back of a combine and disengage the spreaders.”

The Australians also use a bale direct weed seed system. A large baleris trailed by the combine, and all straw, weed seed and chaff is baled and hauled offsite for livestock consumption. Norsworthy contends a bale 
direct system might not be a long-term solution because of the possibility of further spreading resistant weeds, despite the appealing economics. 

“It makes little sense to bale weed seed-heavy material and send it to other farms or states for feedstock,” he says. “However, the bale direct method makes sense on particular acreage if the feedstock doesn’t change locations.”

Chaff carts, windrow burning and bale direct are grabbing the attention of the agriculture industry, but in comparison, the HSD is snapping necks. The pull-behind unit funnels chaff into a cage mill that pulverizes weed seed. 

In 2013, Norsworthy traveled to Australia and met Ray Harrington, inventor of the HSD and a farmer. “Ray was tired of fighting resistant weeds and returning the seed to the soil,” Norsworthy notes. “After several years of tweaking, he designed the HSD.”

Using cage mill technology, the HSD crushes weed seeds and leaves them nonviable. “I watched the seed destructor in action, and I wondered if the HSD would destroy tiny pigweed seed,” Norsworthy says. “Ray asked me, ‘How does pigweed compare with gravel?’ Then he dumped a 5-gal. bucket of gravel into the HSD, and it came out as powder.”

Highly effective in wheat and canola, Walsh believes the HSD will work in all grain crops and has high expectations for 2015 test runs in the U.S. 

Norsworthy is anxious to test the HSD on Palmer amaranth seed in 2015. A robust pigweed plant, growing without much competition, can produce 1 million seeds. Weed control is often a true numbers game, and from just two or three pigweeds on a single acre, a combine can spread 2 million to 3 million seeds across a field. 

“It doesn’t make sense to run weed seeds through a combine and spread them back across a field, but that’s what we’re currently doing,” Norsworthy notes. “Our research has shown that for Palmer amaranth in a field, 99% will go right through the combine. It’s not like they shatter and get in the soil prior to harvest. Why not destroy them as they exit the combine?”

As part of an Extension effort, Norsworthy co-wrote a USDA grant application in 2013 requesting to purchase three HSDs to evaluate in the Midwest, Northeast and South. However, due the $200,000 price tag for a HSD, plus $30,000 for shipping, the three regions will share one seed destructor in 2015.

In less than a decade, the pull-behind HSD might be a standard feature on combines, Norsworthy says. “Some engineers, in conjunction with Harrington, have worked on integrating the HSD into a combine with no equipment to pull,” he adds.

Powles and Walsh emphasize harvest weed seed control strategies are supplemental methods to herbicide controls against resistant weeds. HWSC is directed at seed production at the end of a growing season, followed by targeting weed seedlings with herbicides at the start of a growing season. HWSC is a direct means for a farmer to attack the seedbank and make herbicides more efficient. 

Powles advocates U.S. farmers start with a simple HWSC system to determine which method fits best on their farm. “Try something basic like narrow windrows. Even if a grower doesn’t burn the windrows, he’ll see the direct evidence of weed seed being moved around a field,” Walsh adds. 

Battling weed seed at harvest is increasingly vital as herbicide resistance forces U.S. farmers to make 
preemptive strikes against the soil seedbank. “Let’s not fight the weeds next year,” Norsworthy says. “Let’s take them out now.”