Herbicides may be the dominant means of controlling weeds, but mechanical techniques are getting a lot of attention lately, thanks to some technological breakthroughs.
A multi-region study overseen by the USDA’s Agricultural Research Service has deployed the Harrington Seed Destructor, a machine designed to reduce the weed seed bank while the farmer is harvesting crops. The study is at the halfway point and is showing real promise.
“We’re doing studies on which weed species are the best candidates for a seed destroyer,” said Steven Mirsky, a scientist at USDA’s Sustainable Agricultural Systems Laboratory in Beltsville, Maryland. “We have to save seeds. You need to have weeds that actually hold their seeds.”
The University of Illinois is one of three institutions involved in research on the HSD. The machine, invented in Australia, can either be pulled behind a combine or integrated as part of a combine.
It pulverizes weed seeds that are ejected as part of the chaff, preventing the seeds from germinating the following season. Adam Davis, who is leading the study at the University of Illinois, is getting positive results.
“We have seen significant reductions in amount in weed seed return with HSD of up to 70 to 80%,” Davis said. “There are similar reductions in seedling emergence the following spring.”
In fact, the system has been so successful that Davis has been forced to back off the herbicide rate in order to keep the weed-seed study populations at sufficient levels for his research.
A similar machine is being marketed by the Australian company Seed Terminator, which is looking to produce 100 units for the next harvest season.
“We aim for this to be a future-proof technology platform, able to slot in the latest mill technology available in two, five or 10 years’ time,” said Nick Berry, director of research and development at the company, based in Adelaide. “We have already rolled out three mill designs in three years. We are not done yet."
Berry said the unit can be fitted to new and used John Deere, Case IH, Massey Ferguson, Claas and New Holland headers.
Research continues on new products such as the Duo, manufactured by the German company C.U.L.T.-Kress Cultivation Solutions. Designed largely for vegetable production, its draw is accuracy.
“It cuts away the soil right up to where the seed is planted,” said Marisa Benzle, who was on a team at Michigan State University that studied several mechanical cultivators. “Then you can follow it with a finger weeder or torsion weeder and pull that soil away.”
Mechanical destruction of weed seeds by machines such as the HSD could be an effective tool in reducing herbicide-resistant weed species.
“At our site in Urbana we’re also looking at the impact of the HSD on the rate at which ALS-resistant waterhemp is spreading,” Davis said. “The ultimate goal is to reduce risk in weed management and reduce reliance on herbicides. With the rate of evolution of herbicide resistance increasing and resistant weeds increasing, we’re going to need other tactics to backstop those types of chemical control approaches.
“The weeds that are going to seed in the fall in a system where you’re relying on chemical control most likely are the resistant ones. They’re the ones that have survived your management tactics. So if you can destroy them, then you’re preventing those resistant seeds from getting into the seed bank.”
Simpler methods of removing weed seeds are also being studied. Researchers in Arkansas are testing something called chaff lining, in which the chaff blown out the back of combine is raked into a narrow band. That way, the seeds are concentrated rather than dispersed throughout the field.
“All you need to do to make chaff lining work on your farm is create kind of a funnel on the back of your combine,” Davis said. “You can concentrate your weed management efforts on a smaller portion of the field. It’s a heck of a lot cheaper.”
Some farmers even set the chaff lines on fire to destroy any seeds.
Machines such as the HSD are not a panacea, Davis points out. For example, even if it destroyed every weed seed in a field, other seeds can be blown in from hundreds of feet away.
“Something like Canada thistle would not be a recommended approach,” he said. “It’s also not going to be effective on weed species that are dispersing their seeds before harvest.”
But he is encouraged by the HSD and other mechanical weed-control systems.
“You can reduce your reliance of herbicide as a central weed management tactic,” Davis said. “By diversifying tactics, you can reduce overall risk of weed control failures on your farm.”