University Extension researchers are evaluating how a fairly simple, inexpensive combine modification can give farmers an edge against some of their toughest weeds.
The modification involves chaff lining, a do-it-yourself approach to harvesting weed seed. The practice uses a chute mounted to the back of the combine to funnel chaff and weed seeds into concentrated rows instead of spreading them across the field.
A number of researchers are evaluating the practice to see if it is compatible with Midwest cropping systems, reports Amber Emmons, an Ohio State University graduate student and water quality Extension associate, in an article for GROW.
Along with Ohio, researchers are evaluating the system in other states, including Arkansas, Kansas, Illinois and Iowa.
A USDA-funded project led by Iowa State University Extension weed scientist Prashant Jha shows the practice can concentrate more than 95% of waterhemp seed into a narrow row — putting a field’s weed seed where farmers can more easily manage it post-harvest.
The Value of Weed Seed Concentration
During conventional harvest, combines scatter chaff — and any weed seeds mixed in —across the field. Chaff lining redirects that material into narrow bands in as little as 5% of a field’s area, notes Emmons.
That concentration creates new, and potentially easier, management opportunities. Farmers could pair chaff lining with target sprayers to concentrate weeds into specific areas, and then treat only the emerged weeds in those areas with herbicides. The concentrated rows could also make other post-harvest treatments more practical.
The modification itself is relatively affordable. Many farmers can make chaff lining chutes with material using supplies they already have on hand or with an investment of $500 to $1,000 in new materials. The Ohio State research chute cost less than $200 to make because researchers already had much of what they needed.
“You make this relatively cheap and simple modification to your combine and you stop exacerbating the [weed] problem,” notes Eugene Law, assistant professor of weed ecology in Ohio State’s Department of Horticulture and Crop Science.
Second-Year Research Expands
In Ohio, the Ohio Soybean Council-funded research is entering its second year, focusing on problem weeds including giant ragweed and waterhemp. Researchers there are evaluating how chaff lining fits with farmers’ existing herbicide programs.
Early findings underscore the continued importance of robust herbicide programs, Emmons notes. A combination of preemergence and postemergence herbicides are still critical for protecting corn and soybean yields.
“Chaff lining could provide another layer of weed management by capturing weed seeds that remain on plants at harvest and concentrating them in rows where they can be treated later,” she says in an article for GROW.
Finding the Right Chaff Density
Researchers are working to determine how much chaff is needed to suppress weed emergence.
During their first chaff-lining harvest, Emmons and Law were surprised to find only slightly more chaff behind the combine than with no chute. However, they suspect the chute still concentrated weed seeds, because lightweight seeds blow farther from combines during conventional harvest than heavier chaff.
Early results reveal a balancing act: Small amounts of chaff can actually insulate and protect weed seeds, while larger amounts reduce germination of some species, including waterhemp.
Ohio researchers found that reducing waterhemp emergence by 90% required chaff density equivalent to a 100-bushel-per-acre soybean crop. More typical Ohio yields of about 50 bushels per acre produce less chaff but could still reduce seed germination and gradually impact the weed seedbank.
“We’re trying to see if there’s an amount of chaff needed to suppress certain weeds,” Emmons says.
Challenges and Opportunities
Unlike seed impact mills — which pulverize weed seeds as they pass through the combine — chaff lining doesn’t immediately destroy seeds. Instead, it concentrates them, requiring farmers to manage chaff rows later when weeds emerge.
That also means less research data exists on how chaff lining affects growers’ weed seedbanks compared with impact mills, which research shows can substantially reduce waterhemp seed viability.
Impact mills come with significant drawbacks, however. Purchase prices start around $70,000, and the technology can affect combine performance. Law says chaff lining has attracted less interest from Ohio farmers than impact mills, though, possibly because some farmers are reluctant to modify their combines.
Expanding to Additional Crops and Weeds
The Ohio State team has expanded research into corn fields to collect data on additional weed species, including foxtail, marestail (horseweed) and barnyardgrass.
Researchers there are also examining whether chaff lining could help manage Italian ryegrass, an increasingly troublesome weed resistant to as many as seven herbicide modes of action.
Law believes harvest timing could make chaff lining particularly valuable against Italian ryegrass in wheat. Wheat harvest typically occurs before Italian ryegrass seed drops to the soil, creating an opportunity to capture seeds with the combine and concentrate them in chaff rows.
By corn and soybean harvest, however, Italian ryegrass seed has often already fallen to the ground, potentially limiting chaff lining’s effectiveness in those crops.
Law sees the adoption of chaff lining as requiring a modest change with cumulative benefits.
“Chaff lining is a small tweak that provides an accelerating impact on your weed seedbank,” he says.
Additional research, he adds, will help determine where chaff lining fits best in farmers’ cropping systems and how effectively they can use it as part of their integrated weed-management programs.
Explore GROW’s website for more information on harvest weed seed control, chaff lining, and seed impact mills.
