Features Agronomy Identity Preserved
Foundation of herbicide may help corn yields

According to Dr. Clarence Swanton, at the Department of Plant Agriculture at the University of Guelph, corn growers need to start thinking about weeds long before they appear.

Swanton, who has been studying the impact of weeds on corn seedlings for several years, believes that corn seedlings can detect the presence of weeds and will alter their growth pattern in response, which may have an effect on crop yield potential.

There can be significant yield loss (0.5 to 3.0 bushels per day) if weeds are not controlled in corn between the three leaf (right) and eight leaf (left) stage, Syngenta’s Paul Cowan told growers at its Honeywood research farm in September.

In studies conducted by Swanton and his associates at the university, corn seedlings detect changes in light quality that are caused by the presence of weeds, and adjust their biomass allocation and leaf orientation in response. “We believe that as a young seedling emerges through the ground, it very quickly starts to sense the environment,” Swanton explains. “As a seedling comes out of the ground and detects weeds, it senses that competition and triggers the shade avoidance response.”

The studies also revealed that weed competition had an impact on seedling growth and development. Corn seedlings emerging with weeds experienced a 0.2 gram reduction in biomass per day relative to weed-free seedlings. Seedlings that had weedy competitors emerge after the three to four leaf tip stage, meanwhile, did not elicit a similar response.

What does this mean for growers? “This has direct relevance to day-to-day decisions when it comes to weed management on farms,” says Swanton. “When a seedling comes out of the ground, you don’t want it seeing green material. If weeds are emerging at the same time, the plant will respond to the pending competition and change its growth pattern.”

While many growers are aware of the importance of early season weed control, Swanton wants farmers to know it is not only a question of killing weeds once they have grown: prevention is key to avoiding critical damage at the seedling stage. “Weeds that emerge with the crop are especially troublesome for competition,” he explains. “Preventative action is critical because of how weeds and the crop interact at a very early stage.”

The new research is helping some corn growers look at their herbicide program in a new way: as a tool to manage plant health and encourage strong yields. “At Syngenta, we call this the Foundation Acre,” explains Kristine Savage, corn and bean crop manager at Syngenta Crop Protection. “It’s about laying the foundation for a healthy crop by ensuring your seedling corn plant does not even ‘see’ weeds, thereby avoiding critical damage at the seedling stage. The best thing growers can do is use a Foundation Acre approach with Primextra II Magnum.”

According to Savage, “More growers of both conventional and glyphosate tolerant corn systems are spraying Primextra early and selecting a glyphosate or Callisto for the balance of their herbicide program. That is the yield management approach of the Foundation Acre.”

Corn growers such as Tom Oogema in St. Thomas, Ontario, are making practical use of this knowledge. “Swanton’s research makes sense, so I apply his teachings to my field,” Oogema explains. “It’s important to treat corn at an early stage to prevent weeds, and then it’s a question of helping the crops come through.” -end-