The sooner you close the crop canopy, the less weed biomass will likely develop in that field. That, in turn, should result in higher yields, says Bhagirath Chauhan, an Australian weed researcher.
He has looked at the effects of canopy closure in several crops, including cotton and soybeans. The more evenly spaced plants are, the more they suppress weed development, he finds.
If anything, tight and even plant spacing and narrower rows do more to suppress weeds than simply increasing crop seeding rates, he contends.
Bhagirath, Principal Research Fellow with the Queensland Alliance for Agriculture and Food Innovation (QAAFI), shared his findings in a recent report on the WeedSmart web site, which covers herbicide resistance issues in Australian agriculture.
Planting cotton at about a 20-inch row spacing clearly reduce weed biomass compared to a 40-inch spacing, although he adds that Australian growers aren’t set up to pick cotton planted in that configuration.
As the article’s author, Cindy Benjamin, observed: “(T)here is now a focus on finding alternative herbicide chemistry to manage the risk of glyphosate-resistant weeds in cotton systems.”
Newer preemerge herbicides will play a part in resistance management, but Chauhan says proper application timing will be the challenge. That means taking into account the effects of rainfall, irrigation timing and soil type, he says.
“There are emerging weeds such as feathertop Rhodes grass, sesbania and amaranth that are challenging the Roundup Ready cropping system, so growers need to have other weed management tactics in place early,” he says.
Australia’s cotton industry is promoting the adoption of a “2 + 2 + 0” weed management system to protect glyphosate and Round-Up Ready varieties. That means using 2 non-glyphosate herbicide alternatives, 2 non-herbicide tactics and accepting nothing less than zero weed survivorship.
Re-introducing preemerge herbicides in cotton production will be important in future weed management programs, Benjamin writes. “Increasing crop competition is also worth further investigation, given the potential weed control and crop yield benefits to be gained if the limitations of current harvesting equipment can be addressed.”
Peter Newman, communication lead with Australian Herbicide Resistance Initiative, has long promoted crop competition in cereal crops. Recent findings by Chauhan and others in summer crops gives growers a valuable non-herbicide tool that will contribute to weed suppression.
“Over and over we are seeing results come from crop competition trials showing suppression of weed biomass in competitive crops, and usually a yield benefit,” he says. “This is a win-win for growers and needs to become standard practice in all crops – not only regarding row width but all agronomic practices that boost early crop growth and result in early canopy closure.”