When it comes to weed control, should growers plant soybeans later in fields where high levels of waterhemp are anticipated?
Over the last decade, soybean planting dates have moved up considerably as new research has shown the oilseed can handle cooler soils and deliver more bushels when planted earlier. But during that same period, the scourge of waterhemp has gained a foothold in many areas of Ontario, with growers really struggling to control the weed in specific fields.
Research from University of Guelph weed scientist Dr. Peter Sikkema reveals that the average yield impact of waterhemp is 43 per cent, but he has documented losses of up to 100 per cent in the most competitive environments. For corn, the average loss is 19 per cent, but in soybeans, losses can reach up to 100 per cent. He notes that most of the time weeds are more competitive in corn, but waterhemp tends to be more competitive in soybeans where it can canopy over the top of the crop.
Sikkema maintains that growers struggling with the yield robber should consider Fierce herbicide, which has consistently delivered the best control in soil-applied pre-emergent herbicide trials, when tackling waterhemp. Many growers, however, consider other options, including Authority Supreme, Boundary and TriActor due to the potential for Fierce crop injury in cool, wet planting conditions.
Sikkema notes that growers who plant Enlist E3 or Xtend soybean seed technology do have post-emerge herbicide options to control later flushes of waterhemp, but starting clean with a soil-applied herbicide and staying clean as long as possible does provide advantages.
Following this logic, Pioneer Seeds Canada agronomist John Seliga wonders if it makes sense to combine herbicide efficacy and planting timing to build a more effective strategy in soybean fields where growers see heavy waterhemp pressure. At a Ridgetown agribusiness breakfast meeting earlier this month, Sikkema suggested that planting later in these fields would allow growers to benefit from Fierce control and mitigate the possibility of the herbicide causing injury.
Sikkema suggested the strategy is “really reasonable” for fields with heavy water hemp pressure. He’s a big believer in starting with the herbicide that offers the best control. With an effective burndown in conventional and no-till soybeans to control the first weed flush, planting May 25 with Fierce versus May 5 with a less efficacious product, makes a lot of sense. He also noted that in cool conditions both crop seeds and weed seeds react similarity to the environment, so waterhemp would also see delayed development.
Applying a product like Fierce also makes sense for extending the waterhemp control window, said University of Guelph weed scientist Dr. Isabelle Aicklen. She noted that pushing back planting would provide an opportunity for the herbicide to be active during a larger portion of waterhemp seed’s lengthy germination window.
Seliga noted that managing waterhemp is a multi-year project, and after the discussion, he agreed that planting later for specific fields and utilizing the most efficacious herbicide could be a key part of an effective control strategy for growers.
