Canola School: Economic thresholds aren't just for insects

Many farmers are familiar with consulting economic threshold charts when it comes time to control insects, but many may be surprised to learn that there are economic thresholds for other pests, too.

Gregory Sekulic, agronomy specialist with the Canola Council of Canada, explains in this Canola School episode that although spraying is an important tool, and vital for food production, it’s time we really start paying attention to economic thresholds — for both weeds and insects.

“When the decision is made to apply a pesticide, be it a fungicide, insecticide, or herbicide, it’s important to have some sort of decision matrix involved. Don’t just go spraying because you have the system that can apply the product and absorb the pesticide and thrive. Really do pay attention to those economic thresholds. And they do really largely exist for all of our insect species, and pest species for sure,” he explains.

However, economic thresholds aren’t just for insects. They also exist for weeds, which is something many producers don’t often think of.

“They go back a number of years now in terms of individual and specific weeds,” Sekulic says. “The pursuit towards extremely clean and weed-free fields is actually wasting a pretty substantial amount of money. Depending when these applications are made, they could be compromising more yield than the weeds that they are removing.” (Story continues below video)

Yield damage done by weeds that emerge before the crop is far worse than from weeds that emerge after and even weeks after the crop. Neil Harker, with Agriculture and Agri-Food Canada (AAFC), says that two weeds that emerge a week before the crop is actually far more damaging than 100 weeds that emerge two weeks after the crop does.

“The drive and the push towards completely weed-free fields is in many cases wasting money on applications that just really aren’t required, but also those extra applications of a product they are making increase the selection pressure for resistance,” Sekulic says.

So how do we develop this decision matrix? How can we ensure that we are in fact, spraying only when it is required? For insects, it’s pretty straight forward. It’s a matter of scouting, sweeping, and making sure the insect is there in high enough numbers to warrant a pesticide application. As Sekulic explains, it becomes a little more tricky when we start talking about economic thresholds for weeds.

“The data supports more timing of weed control. So what we do what to make sure when we are doing our herbicide applications, is that we are doing it early, and substantially earlier than our surveys are indicating people are doing it,” he says. “Definitely before the two-leaf stage, and not long after emergence is when we want to see our weed control pass done. That’s when our yield is going to be maximized. The longer we can keep that emerging crop from the competition, the higher the yields are.”

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