From the perch in his combine in central Illinois, Matt Hughes scanned the surrounding fields. So far, Palmer amaranth was nowhere in sight. But since neighboring farmers own land in the other parts of the state where the dreaded pigweed has surfaced, Hughes is resigned to an eventual invasion.
“I guess we’ll probably have Palmer by this time next year,” he said. “It might work its way up here by nature, but it’s probably going to come through equipment,” he added.
This is the time of year when combines double as both harvesting tools and highly efficient weed seed spreaders, weed scientists confirmed.
“Combines are great weed-spreaders,” University of Tennessee weed scientist Larry Steckel told DTN. “In fact, they are the major way weeds are spread.”
The combine’s stalk choppers function as a weed broadcasting tool, fanning the weed seed out across the field behind the machine, Steckel explained. Weed seed can also get caught in the combine and travel from field to field, infesting an entire farm in short order, he added.
While dodging every weed escape in the field might be impossible, harvesting around large patches of weeds might be well worth your time, particularly if the weed patch has overtaken the row crop, Steckel said. Wet spots in fields often become the equivalent of a weed oasis, too. This year’s wet spring provided plenty of opportunities for weeds to get a foothold.
The key to future control is keeping the weed seed in that one isolated patch, Steckel explained.
“Just leave those areas,” he urged. “You’re just spreading that [weed] out as you go through the field, so next year you’re going to have a nice distribution of them instead of the small patch you’re able to manage.”
Be sure to blow your combine out carefully before leaving the field, Steckel said. University of Illinois weed scientist Aaron Hager recommends cleaning the machine in areas away from the field, such as a grass border, a field road, or somewhere where water is unlikely to wash it back into your field.
Better yet, save your weediest fields for last, so you don’t risk carrying weed seed into cleaner fields, Steckel added.
After harvest, farmers have a few options for dealing with the standing weed patches.
“For Palmer, we suggest leaving them alone and not working the field this fall,” Hager told DTN in an email. “That way, most of the seed remains near the soil surface where it is subjected to all the various processes responsible for seed degradation.” Studies at the University of Illinois have shown that insects, mice and even earthworms all take a toll on weed seeds left on top of the ground.
When flooded fields left Hughes with large patches of waterhemp last year, he carefully mowed down the patches after harvest and blew out the mowers in his field. “In the spring we will put chemicals on and we want that bare ground, so the chemicals get onto the soil,” he explained. “We don’t want standing weeds there that would interfere with that contact.”
Farmers sometimes opt to burn the patch in the fall, but the fire has to be hot enough and long-lived enough to destroy the seed viability, Hager noted.
Cutting and transporting the weeds out of the field is riskier, he added. “I’ve always been worried about cutting plants and hauling them from the field since it’s almost a guarantee that you will turn yourself into a seed vector,” he said.
From your perch on the combine, you can also use the fall harvest as an intelligence gathering operation on your weed situation, Steckel added. “Make a note of which weeds are in which fields,” he advised. “Then in the winter, when you start making a game plan for what crops you’ll grow and what inputs you’ll use, start factoring in the weed potential in the field, too.”