When professor Adam Davis looks at a combine, he sees one of the most effective weed seed spreaders ever made. But the head of the Department of Crop Sciences at the University of Illinois says new techniques for harvesting and destroying seeds popularized in Australia are changing the harvester’s reputation, turning combines into important tools for physically reducing weed populations that are becoming increasingly resistant to chemicals.

A USDA-Agricultural Research Service area-wide integrated weed control study started in 2015 is investigating weed harvesting and destruction tactics deployed in Australia and applying them to U.S. fields. Davis is one of the leaders and has spent his time testing a prototype of the Harrington Seed Destructor, which separates and mills weed seed in a pull-behind unit.

“Just in a stationary trial, for the seed that gets into the mill, we were reducing seed viability by like 99.99%. We were really messing them up,” Davis says, adding that in the nine different species of weed seed he tested, even nearly undetectable scratches would open up seed for microbes to feast on over the winter.

He’s also used the prototype during harvest, successfully taking in and destroying 80% of the waterhemp seeds lodged in the soil seed bank of one field.

That’s good news for farmers fighting weed resistance.

“We're trying to prevent weed seed from going back into the soil seed bank because we understand as seed numbers increase in the seed bank, our risk for herbicide resistance likewise increases,” says Jason Norsworthy, the Arkansas leader on the area-wide study.

Integrated seed destruction
The manufacturer of the seed destructor, De Bruin Engineering, Australia, has moved away from the pull-behind design pictured here and now only sells a system that can be integrated into a grower’s combine.

“But it’s the same general idea: capturing weed seeds at the time of crop harvest,” Davis says.

The integrated system has been available for some time for Australian farmers. A spokesperson for De Bruin says the company will release a limited quantity in the U.S. ahead of the next growing season. Norsworthy, a professor at the University of Arkansas, just had it installed on one of his Class 7 combines and is assessing its performance.

“I'm optimistic that here in a couple of years, when a grower goes to purchase a combine, or even with a combine they have, that they should be able to purchase separately an Integrated Harrington Seed Destructor and have that installed,” Norsworthy says.

Davis adds that if the integrated destructors are eventually offered as a rentable service in the U.S., he’d want to see the combines steam-cleaned between fields.

“Resistance can evolve due to herbicide overuse on a given farm, but it can also capture a farm just through immigration too,” he says.

Other ways to destroy weed seeds
Over the past three years of the area-wide study, while Davis experimented with the prototype version of the destructor, Norsworthy focused on techniques that can be deployed today by U.S. farmers to reduce weed populations.

As combines harvest everything in a field, they reduce weed seeds into light-weight chaff that can be separated and fed into a cart, or into a narrow windrow.

“Narrow windrow burning is a widely used concept over in Australia, where you have a chute on the back of the combine that funnels the material into a very narrow windrow, and that material can then be burned, killing all the weed seed,” Norsworthy says. “It’s a very inexpensive method, and again, results in killing 100% of the weed seed that’s harvested.”

Norsworthy says over the past three years, 50,000 acres of farmland in northeast Arkansas and southern Missouri have taken up narrow windrow burning to fight glyphosate-resistant Palmer amaranth, which is also a problem weed for Illinois farmers.

“We can take a very effective herbicide program and we can bring down the soil seed bank with that program. We may be able to bring it down 20- to 25-fold versus that of a program that is failing,” Norsworthy says. “And we can bring it down another fourfold on top of that by combining it with narrow windrow burning.”

In the end, this multipronged attack on weed seeds might just shift the combine from the worst weed seed spreader to the best weed-resistance fighter.

Update: October 4, 2018

This article has been updated to reflect the planned limited release of the Integrated Harrington Seed Destructor in the U.S. by De Bruin Engineering.