Covering up weed seeds

Input savings, soil health are among the benefits of cover crops

Start simple with cover crops and choose species based on goals.

Cover crops are not free, but they don’t have to be a cost. In fact, they can save farmers money.

Researchers and farmers talked about the benefits during a recent session hosted by the Ontario Soil and Crop Improvement Association. While there is always variability, weed suppression and population reduction are the chief – though not necessarily only – ways cover crops can better a farm’s bottom line. 

Why it matters: Cover cropping could be justified as another tool to help keep down weed populations as farmers struggle with more herbicide-resistant weeds.

More weeds equal more weed seeds if left uncontrolled. Over time, the weed seed bank within a given area can be substantial, requiring more time, resources and cash to address the problem. Herbicide-tolerant weeds can increase the price tag of effective control. 

Francois Tardif, professor of plant agriculture with the University of Guelph and one of the session speakers, describes bare soil as the environment in which weed seeds are happiest. The light-blocking residue of cover crops adds stress. 

Cover crops thus help control the development of the weed seed bank at germination and emergence. After making it harder to get started, covers also effectively compete with weeds for resources. 

The one-two punch of a less-than-ideal environment for weed development and higher competition is further augmented by allelopathy, the ability of some cover crops to inhibit weed growth through the production of toxic compounds. 

The phenomenon is not consistent, however. 

Tardif equates allelopathy with applying a herbicide with variable concentrations. Sometimes the cover crop is very effective at inhibiting weed growth but other times less so. Regardless, he says establishing dense covers earlier has a significant impact on weed pressure. 

Like Tardif, Mike Cowbrough, weed management specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs, says bare soil is not ideal for weed management. 

Ontario generally has 1.5 million acres of soybeans and dry beans not seeded to winter wheat in a given year. While some will be planted with cover crops, a significant amount remains uncovered. Collectively, it has a substantial impact on weed germination, development and spread.

Cover crops don’t have to be expensive or complex to have noticeable impacts. Cowbrough’s work shows oats, a comparatively cheap and available cover crop option, broadcast with potash at 50 pounds per acre, add an extra $16 per acre to production costs. Weed populations were much lower. 

Cowbrough says cereal rye is another cheap “gateway” cover crop option that can drastically reduce weed populations, including those of common and problematic pigweed species, lamb’s quarters and others. 

Even when the allelopathic process is not particularly effective, he says cover crops are a valuable tool in the agronomic box. 

“Smaller plants are much easier to kill with your herbicide program,” says Cowbrough. 

Two farmers, Charlene Whattam from Douglas and Mark Burnham of Cobourg, participated in the recent event as session speakers. 

Whattam considers herself new to cover cropping, though she found them valuable as a source of forage after making a deal with a neighbouring dairy farmer. The weed suppression was also noticeable and valued.

For Burnham, the erosion prevention provided by cover crops has been invaluable. Aside from ecological benefits, he says they saved time and money that was otherwise spent on fixing washouts. He also says the soil is “more mellow” and easier to plant overall, which brings further production savings. 

Yield wise, he believes cover crops brought equal if not higher returns.

About the author


Matt McIntosh

Matt is a freelance writer based between Essex County and Chatham-Kent. He is interested in all things scientific, as well as rock n' roll, hunting and history. He also works with his parents on their sixth-generation family farm.



Stories from our other publications