When producers harvest their corn and soybeans in the not-too-distant future, they may hear a steady roar coming from the rear of the combine. If they’ve just purchased a combine with an integrated Harrington Seed Destructor (HSD) option, those extra decibels won’t bother them a bit.
It will be the sound of resistant weed seeds turning into dust or something very much like it. That could include seeds from waterhemp and Palmer pigweed, just to name a couple. If anything, all the extra noise will be music to the farmer’s ear.
Combines with the integrated HSD option are currently available and operating in Australia. You can see one here. The HSD was invented by western Australia farmer Ray Harrington and it’s gained the attention of weed researchers in the United States, as well.
Upon entering the HSD, weed seeds pass through two counter-rotating cages, spinning at 1,500 revolutions per minute. The violent motion cracks nearly every weed seed that makes it into the chamber.
U.S. scientists in 3 regions have been closely testing this system for at least 2 years now and have drawn a number of conclusions:
- The system works.
- Once a seed flows into the HSD, it’s pretty much toast, as one weed scientist puts it.
- The HSD reduced waterhemp seed entering the soil seed bank by 80%.
- It does a number on Palmer pigweed seed, as well.
An integrated HSD might be commercialized in the U.S. in a couple of years (although the design may differ slightly from anything being tested now).
Weed scientists in the U.S. have been running HSD at a number of test sites, with machines based in Illinois, Maryland and Arkansas. USDA’s Agricultural Research Service (ARS) funds the evaluations through a program that focuses on integrated weed management.
Test sites include 4 in the north-central U.S., 5 in the south-central states and 5 in the mid-Atlantic region.
Among other things, weed scientists want to determine if seed destructor technology will work across a range of U.S. geographies and crops.
How Many Seed Are Getting Away?
They’re also hoping to determine to what extent weed seeds shatter ahead of harvest. When that happens, the seeds never make it into the combine and escape the HSD.
“We’re measuring the timing of weed seed rain – meaning, the shattering of seed – for the dominant weed species in each of these locations,” says Adam Davis, a USDA research ecologist at University of Illinois at Champaign-Urbana. “We want to know what proportion of seeds will be captured by the HSD at each location.”
So far, the percentages vary widely among weed species. But across most locations, both waterhemp and Palmer amaranth are still carrying as much as 95% of their seed when the combine reaches the plants.
“Other weeds like giant foxtail don’t do so well since they drop their seeds well ahead of soybean harvest,” Davis notes. “Common lambsquarters holds up very well and giant ragweed seems to vary by year.”
A High “Kill” Rate
Scientists working in the 3 regions found that the HSD kills nearly all the weed seed it captures. “It’s about 99.99%,” Davis says. “Any weed seed that enters the HSD is pretty much toast.”
Jason Norsworthy, Extension weed scientist at the University of Arkansas, is testing an integrated HSD as a stationary unit. His team feeds chaff and weed seed into the unit to simulate an HSD-equipped combine running through the field at harvest. In Arkansas, he’s seen similar results to Davis, with over a 99% kill rate for Palmer amaranth seed.
The scientists are also collaborating on a longer-term study of the HSD’s effect on weed populations and weed resistance. University of Illinois researchers reported an 80% reduction in ALS-resistant waterhemp seed returned to the soil with a tow-behind HSD.
Davis believes the 20% of the seed that dropped to the ground could be the result of early shattering or shattering on impact with the combine head.
Can Weeds Gain “Resistance” To Grinding?
Concerns have been raised about selecting weed populations that shatter early, depositing seed on the soil surface ahead of harvest. Australian studies over an 8-year period demonstrated that there was some selection pressure for early shattering in rigid ryegrass when the HSD ran year after year.
“I think we’ll see that in the U.S. too,” Davis says. “If you use the HSD only on soybeans in the corn and soybean rotation, you would be putting a little less pressure on weeds.”
But there could be a so-called fitness cost where early shattering is selected.
“For early shattering to occur, the mother plant would have to become mature and senesce earlier,” Davis said. “That would actually shorten the growth period for that weed. So, it’s possible you could end up with Palmer amaranth or waterhemp being boxed into a shorter part of the growing season. That might mean it would put on less biomass by the time it becomes reproductive.”
How Practical And How Much?
University of Illinois researchers have just completed 2 years of study on the tow-behind HSD, which they plumbed into a John Deere 9410 combine. While the tow-behind is effective, Davis doesn’t see it as a commercial option.
“It’s very large and is another piece of machinery to house and maintain,” he explains. “And you also have to be a fairly skilled metal fabricator to plumb it into the combine.”
Norsworthy says that the integrated HSD could be turned on and off as the combine moves through the field. “If you have a relatively clean field, turn it off and keep going. If you reach a few weeds out there and you want to make sure they’re non-viable, turn it on.”
Another combine-integrated seed destroyer called the Seed Terminator was developed by Australian engineer Nick Berry. It uses a series of hammer mills to pulverize seeds, which must pass through a series of progressively smaller screens. The Seed Terminator was commercialized in 2017 and can be fitted onto a Class 7 combine, according to its website.
The integrated HSD Norsworthy is testing in Arkansas is designed for larger Class 8, 9 or 10 combines and will require a redesign for the Class 7 combine which is popular in the United States. The integrated HSD for the larger combines is hydraulically-driven, but the manufacturer, DeBruin Engineering in Australia, is considering a mechanically-driven HSD for Class 7 combines.
The HSD requires 80 to 90 horsepower. Norsworthy thinks the integrated HSD is still a couple of years from commercialization.
Davis doesn’t see the HSD as a “silver bullet” for managing resistant weeds, “but it could be a useful component of an integrated weed management system.”
Norsworthy believes an integrated HSD in combines could be cost-effective for U.S. producers at around $75,000. “Distribute that over 3,000 to 4,000 acres and you’ve got less than the cost of a herbicide application in the cost of running the HSD.”