If it’s a weed, spray it. That’s the mindset that most in the agriculture industry held for years.
That thinking no longer works as more weeds become resistant to herbicides, said Kevin Bradley, University of Missouri Extension weed scientist.
Bradley uses waterhemp as an example. Waterhemp is one of 14 herbicide-resistant weed species in Missouri. It is a prolific producer of seeds, and Bradley considers it Missouri’s most worrisome weed.
“It’s clear that we need a new approach,” he said.
MU Extension researchers are looking at how to remove weeds without herbicides. One non-chemical method is electrocution.
The Weed Zapper, made in Sedalia, Missouri, is used mostly in organic operations, but it may also work in conventional pasture and row crops. Mizzou has used the Weed Zapper on test plots and saw 98.6% effectiveness in waterhemp destruction.
The Weed Zapper’s copper boom attaches to the front of a tractor and hits weeds with 15,000 volts of electricity from a 110,000-watt generator on the back of the tractor.
Bradley noted that the Weed Zapper can be dangerous because of its voltage. It also can have negative effect on soybean yield if a lot of the foliage is contacted by the boom in later growth stages.
Its effects are immediate and deadly, especially on larger weeds. It works best when used at seven-day intervals rather than in a single pass.
It is most effective on waterhemp, ragweeds, horseweeds and cocklebur. It is less effective on foxtail and barnyardgrass.
“It’s not a silver bullet, but it is very effective on several of our most troublesome weed species,” Bradley said.
Commonly used in Australia, narrow-windrow burning poses a viable option for commons weeds, including Palmer amaranth, barnyardgrass, johnsongrass, pitted morningglory, prickly sida, Italian ryegrass, sicklepod, velvetleaf and hemp sesbania.
Several universities, including Louisiana State University, the University of Arkansas and MU are comparing how these alternative non-chemical control measures affect weed populations.
The narrow-windrow burning system is simple and is the most effective harvest weed seed control tactic, according to University of Arkansas researchers. The inexpensive system uses a chute mounted on the rear of the combine that concentrates the chaff into a narrow row. The base of the chute is generally 16 to 18 inches wide.
Immediately following formation, the rows should be burned. Burning the entire field is not as effective in killing the weed seeds as burning the chaff in the windrows.
The concentration of the chaff increases the temperature and duration of burning, which leaves less loss of residue versus traditional burning Unlike other combine add-ons, this system does not slow harvest.
In soybeans, narrow windrow burning has been shown to reduce escaped Palmer amaranth by 73% and the soil seedbank by 62% over three years, according to research led by UArk’s Dr. Jason Norsworthy.
Another option is the Seed Terminator. This seed control tool attaches to the back of a combine. Its dual hammer mills crush the chaff through stationary and rotating bars to make it nonviable.
Bradley says there is a need for more research to understand how new technologies can best reduce weeds in U.S. soybean.
Seed destruction is popular in Australia but not widely used in the United States.
Weeds such as waterhemp, Missouri’s No. 1 weed, can exit the combine in areas such as the header and grain tank. In fact, Bradley said about two-thirds of the seed goes out the back of the combine. Multi-state studies are underway to look at how to reduce the number of seeds making it to the soil.
It might take several seasons of use to see substantial reductions, Bradley said.
Most seed that goes through the combine, even pinhead-sized waterhemp and palmer amaranth seeds, becomes nonviable.
Increased engine load on the combine raises fuel consumption an average of 4.1 gallons per hour.
Funding for this research project comes from the Seed Terminator, Mizzou Weed Science, United Soybean Board, Missouri Soybeans and Case IH Agriculture.
Graduate students Travis Winans and Haylee Schreier work with Bradley on the research.
The University of Missouri contributed information for this article.