Researchers seek ways to control perennial weeds in organic fields

WOOSTER, Ohio – Ohio State University scientists have received a four-year, $400,000 USDA grant to tackle a deep-rooted thorn in organic farming’s side.
Crop scientist John Cardina and colleagues will target perennial weeds – specifically, how to control them without using synthetic weed killers.
They’ll also be looking at how those methods affect crops, the soil and a farmer’s bottom line.
The work will focus on vegetable crops, which tend to fare poorly when competing with weeds, and on the three-year transition period from conventional to organic production.
The project will evaluate transition strategies that both improve the soil and control perennial weeds.
Farmers pushing. Spurring the effort: farmers’ concerns, voiced at field days and other events and borne out by a survey of 22 Ohio organic vegetable farms that found perennial-weed species, not annual ones, were most likely to be poorly controlled by current methods.
Farmers helped develop the plan, including selecting which treatments to study. Their farms will host some of the research.
Big problem. The scientists, all with the university’s Organic Food and Farming Education and Research (OFFER) program, call perennial weeds “among the most serious impediments to the adoption, expansion and sustainability of organic farming.”
Long-lived vegetative parts – roots and the like – let perennial weeds regrow quickly after cultivation (a common organic way to fight weeds) and survive in a place year after year.
Annual weeds don’t do that. Cultivation usually wipes them out, lock, stock, barrel and root. They survive to the next year only through their seeds.
Quackgrass, bindweeds, Canada thistle and yellow nutsedge rank among the culprits. So do pokeweed, hemp dogbane, Johnsongrass and broadleaf dock.
All in the timing. “Our central hypothesis,” the scientists said, “is that biologically based and properly timed control efforts, integrated with soil-building measures, will provide effective and economical transition strategies that can be readily adopted by organic and transitioning farmers.”
They’ll test that hypothesis at the university’s Ohio Agricultural Research and Development Center in Wooster and in on-farm studies – on a half dozen or so Ohio organic farms
“The on-farm studies will follow perennial weed populations in whatever rotation and management strategy the cooperating farmers choose to use,” Cardina said. “We want to learn how perennial weeds respond to real-life farming situations and how farmers respond to changes in those weed populations.”
The project will look at a range of crops, including peas, squash, lettuce, sweet corn, potatoes, and tomatoes. Each particular strategy tested will determine the crops that get used.
“For example, one strategy will be clean fallow with soil-building cover crops during the three-year transition period,” Cardina said. “At the other extreme will be multiple cropping with tomato and cabbage in year 1, bell pepper and broccoli in year 2, and squash and lettuce in year 3.