In the battle against herbicide-resistant weeds, farmers are increasingly eager to add non-chemical control methods to their management toolbox.
Impact mills, which destroy weed seeds picked up by a combine, have been shown to kill 70 to 99% of weed seeds in soybeans, wheat and other small-statured cropping systems. And a recent Weed Science study from the University of Illinois shows even seeds that appear unscathed after impact milling don't germinate the following spring.
Study co-author and head of U of I's Department of Crop Science Adam Davis and his collaborators wanted to see how the Harrington Seed Destructor, an impact mill developed and widely used in Australia, handled common U.S. agronomic weeds without the complications of real field conditions.
The researchers collected seeds from 10 common weed species in soybean fields in the Midwest and Mid-Atlantic regions, fed the seeds through a stationary HSD and then tried germinating them in a greenhouse and in the field.
Davis said up to 15% of the seeds appeared to be undamaged immediately after milling, regardless of species and seed size. But when the undamaged seeds were buried in the field and left through the winter, less than 10% survived because, based on previous research, Davis thinks microscopic abrasions from the mill damage the seed coat enough for microbes to enter and destroy the embryonic seed inside.
But producers probably can't expect nearly zero weed seed survival when using the HSD or other impact mills in the field.
Davis and his collaborators have been conducting field trials with the HSD for five years and typically see a reduction in weed seed survival by 70 to 80%.
"The difference between its efficacy as a stationary device and its efficacy in the field is largely due to shattering of the seeds," David said. "As the combine is going through, it's shaking everything and causing a lot of seed dispersal. By looking at the HSD as a stationary device, we're able to quantify the theoretical max."
Field research ?results
Researchers from U of I and the Illinois Natural History Survey have published their 2019 field research results related to crop pests and diseases in the state.
The report, "2019 applied research results: Field crop disease and impact management," is available online and includes evaluations of plant varieties, management practices and products for insects, nematodes and diseases in corn and soybean as well as results of statewide pest surveys.
"This annual publication is a nice one-stop-shop for applied research results for the season. It's not just diseases; it's weather, production and insects," said report author Nathan Kleczewski, a plant pathologist in the Department of Crop Sciences and U of I Extension specialist. "In the future, we hope it can continue to expand to include other areas and crops."
The report also includes information on management practices that didn't work.
"In applied research, the lack of an effect of a management practice is just as important as if a practice has an effect," Kleczewski said.
"Management costs money, and we want our producers to be as profitable as possible. If something doesn't work, we want that information out there just as much as if something works."
According to the report, the wet 2019 spring favored fusarium head blight in some areas, and late planting resulted in pockets of corn impacted by southern rust.
Tar spot, a major player in the 2018 season, was not impactful due to dry conditions in the middle of summer, increased prevent-plant acres in the northern part of the state and other environmental factors.
Although diseases in soybeans were not a major issue, soybean cyst nematode still was present in the majority of fields to some degree.