By MICHELE F. MIHALJEVICH
Indiana Correspondent

URBANA, Ill. — Farmers may find that using mechanical rather than chemical methods will best fight persistent weed seeds, a USDA ecologist said.

If farmers want to reduce the rate the weed population is growing, the best way is to concentrate on weed seeds and not the weeds themselves, said Adam Davis, an ecologist with the Invasive Weed Management Unit of the USDA’s Agricultural Research Service.
“From what we’ve seen, if we can find a way to damage the seeds, they would decay a lot faster in the soil seedbank,” he said.

In a recent study, short-lived seeds were found to have higher levels of chemical protection, but lower levels of physical protection, he said. Long-lived or more persistent seeds, however, were found to have lower levels of chemical protection and higher levels of physical protection.

The study was done in Illinois and examined giant foxtail, common lambsquarters, field pennycress, yellow foxtail, kochia and velvetleaf, all common in the state and across the Midwest, he said.

An explanation of the study, written by Davis and three colleagues, was published recently in Weed Science.

Researchers damaged some seeds, either by piercing with a needle or slicing a part of the seed coat, and placed them in the soil for two months.

“With the short-lived seeds, the chemical properties kept the same,” Davis said. “With the longer-lived seeds, everything died.”
Modifying harvest machines to damage the seeds might be a way to destroy them, he said. “We’re trying to take a precise piece of machinery for harvesting and turn it into a seed killing device. It appears very possible to do that.”

Davis is working with a class of mechanical engineering students from the University of Illinois to help develop an after-market kit for combines that will accomplish the goal of damaging the seeds.
“We’re hoping they will come up with a product,” he said. “We’re hoping to have the device by next summer’s Agronomy Day.”
The hope is that such a kit would be easy to use and wouldn’t be cost prohibitive, he said.

“We want to keep (the price) at a level that wouldn’t break the bank. It should be able to be added to an existing combine,” Davis added.

The kit would have to be light, as the amount of damage needed is minimal, he said. “All it takes is a nick. Right now, we’re focusing on sandblasting, which leaves an abrasion area. We’ve also looked at whirling blades.”

Longer-term, the study also looks at how reducing seed population density in a soil seedbank could affect weed management the following year.

“If less chemical management is necessary, it could reduce serial applications of herbicides,” Davis said. “A well-timed spray may do the trick.”