Weed Destruction from Down Under
By Jason Jenkins, Mill Creek Communications
For eight seasons on the Discovery Channel’s popular reality show “Dirty Jobs,” TV host Mike Rowe explored the country looking for people who weren’t afraid to “getdirty.” There’s no doubt that if the show was still being filmed today, Rowe would’ve loved visiting the University of Missouri Weed Science research team this fall.
Rowe could have tried his hand at being the team’s “soybean chaff collector,” a job that requires a mask, gloves, goggles and a willingness to get pummeled point-blank by the discharge from a Class 8 combine.
“It’s definitely one of, if not the dirtiest job I’ve ever had,” says Travis Winans, a graduate student working under the guidance of MU Extension weed scientist Kevin Bradley. “It’s really loud; sounds like there’s an airplane turbine hooked to the combine. And it’s super dusty, but it’s what we need to do to collect our data.”
Winans and the other MU researchers are in their second year of evaluating the efficacy of a weed seed destruction implement called the Seed Terminator. Attached to the rear of a combine, the machine’s purpose is to render weed seed incapable of germination.
“Herbicide-resistant waterhemp is a major concern in Missouri, so we’re looking at other weed-control options for the state’s soybean producers beyond their herbicide program,” Winans says. “The Seed Terminator is one of several harvest weed seed control solutions available today.”
Dropping the hammer on waterhemp
Originally developed in Australia to combat herbicide-resistant Italian ryegrass, the Seed Terminator contains two multistage hammer mills. These mills are composed of both stationary and rotating component groups. During harvest, chaff from the combine’s shoe load enters the Terminator’s inlet chutes that feed into the mills. Flails and rotors spinning at 2,250 to 3,000 rpms force the plant material through a set of three screens, reducing it in size through four modes of action: impact, shearing, crushing and grinding.
“The objective is to damage the waterhemp seed coat to a point where that seed is no longer viable,” Winans explains. “In our evaluation, when half of more of the seed coat is missing, or the seed is less than half the size of a non-damaged seed, we designate that as damaged, non-viable seed.”
The MU team evaluated the Seed Terminator at four sites in mid-Missouri in 2019 and three sites in 2020. All of the sites had been in continuous soybean, though the type of soybeans varied from site to site.
“In 2019, we had two sites where herbicide-tolerant soybeans were planted, one with non-GMO soybeans and one with organic soybeans,” says Winans, noting that the organic site provided the opportunity to evaluate the technology on larger-seeded weeds including velvetleaf, morning glory and foxtail. “In 2020, we returned to three of the four sites. The cooperating producer for the fourth site changed his herbicide program this year, and he didn’t have significant enough weed pressure to evaluate the Seed Terminator.”
At each site, a Case-IH 8250 combine equipped with a 35-foot draper header and the Seed Terminator was used to harvest soybean plots. The MU researchers took six collections from each plot. In non-treated plots — those where the Seed Terminator was not engaged — the team collected samples used to evaluate header loss, threshing loss and straw chopper discharge. In treated plots where material was directed into the Seed Terminator, an additional sample was taken from the device’s discharge ports.
Based on initial findings from the first year of data, the Seed Terminator can deliver on its moniker: When averaged across all four sites in 2019, about 92% of waterhemp seeds that passed through the hammer mills were no longer viable and able to germinate. At some sites, the percentage of seeds damaged surpassed 98%. However, this statistic only tells part of the story.
Many weeds, including waterhemp, begin to shed seeds before it’s time to harvest soybeans. As those weed seeds drop to the ground, they enter the seed bank and have the opportunity to germinate in subsequent years. For those seeds, harvest weed seed control measures like the Seed Terminator are ineffective.
“We also sustain header loss of waterhemp seed,” Winans says. “When the header comes in contact with those plants, the seed gets knocked off and never enters the combine.”
The graduate student adds that even when the waterhemp does enter the combine, a percentage of the weed seed doesn’t reach the hammer mills.
“In 2019, we determined that only about 72% of the waterhemp seed that entered the combine was directed to the Seed Terminator,” he notes. “You’re getting some threshing loss where that seed is coming out through the straw spreader and is not damaged whatsoever.”
In addition to its purchase cost, which is around $75,000 to $80,000, the Seed Terminator also has operating costs. The manufacturer estimates a requirement of 80 to 100 horsepower, and the MU team’s 2019 research showed an increase of 15% to 30% in combine engine load when the hammer mills were engaged. Fuel consumption also went up by 3 to 8 gallons per hour. However, effect on harvest speed was negligible.
Using the Seed Terminator in the same fields year after year would gradually deplete the seed bank and lead to less weed emergence. “If you’ve had historical problems with herbicide resistance, it can be something to look into,” Winans says.
Weed Seed Stoppers
The Seed Terminator is not the only harvest weed seed control (HWSC) technology on the market. The Harrington Seed Destructor is another device that uses mills to grind seeds at about the same effectiveness as the Seed Terminator.
But turning weed seeds into dust isn’t the only means of slowing the spread of herbicide resistance. Other HWSC concepts include narrow windrow burning, where chaff and the weed seeds contained within are consumed by fire following crop harvest; direct bale method, where chaff is baled and removed from the field; and chaff carts, which collect the chaff from the combine. Chaff dumps can be grazed before residue is burned.
Winans says that while all of these methods may have applicability for Missouri soybean producers, the biggest takeaway is that a multipronged strategy to weed management is the only way to combat herbicide resistance and avoid the yield losses that come with weed pressure.
“There haven’t been any new herbicide modes of action since the 1980s, and we’re getting more and more herbicide- resistant weeds,” he says. “There’s not one silver bullet to controlling weeds. You can’t just rely on one herbicide. It takes an integrated approach.”
HWSC methods are just another management tool for producers,
joining crop rotation, cover crops and herbicide programs using pre- and post- emergence products with varying modes of action as means of stopping weeds from growing.
“Any tool a farmer can use to prevent weed seed from returning to the soil surface is valuable,” Winans says.
EDITOR’S NOTE: This is the final article in a yearlong series examining the past, present and future of weed control in the production of soybeans in the Show-Me State. This issue, we take a look at harvest weed seed control methods, including those being evaluated by the University of Missouri Weed Science Program.
Find the December issue of Missouri Farmer Today here.