One pass may handle weeds and flea beetles in canola

As canola pushes through the ground across the Prairies, growers may be watching for two early-season problems at once: weeds that need spraying and flea beetles chewing on young seedlings.

When those jobs line up, the Canola Council of Canada says one sprayer pass may be enough.

Why it Matters: Combining flea beetle and herbicide applications can save time during a busy spray window, but only when economic thresholds, label rules and spray setup all line up.

The first consideration is whether the field is at threshold.

Manitoba Agriculture entomologist John Gavloski said that once canola begins to emerge, farmers should periodically assess levels of injury to plants from flea beetles.

He said seed treatments will provide control for young seedlings, but that control can diminish three to four weeks after seeding. If flea beetles are still actively feeding and the plants have not yet produced a few true leaves, it could be time to consider a foliar insecticide.

“The economic threshold is 25 per cent defoliation and flea beetles still present,” said Gavloski.

“If this economic threshold has been surpassed, and plants are still in stages susceptible to flea beetles, then an insecticide application, either alone or tank-mixed with a herbicide application, would be economical.”

Another consideration is whether the herbicide setup will still work for flea beetle control.

The canola council notes that low-drift herbicide nozzles, which are a good practice for some herbicide applications, produce coarse droplets. Those droplets may not provide the coverage or flea beetle contact needed for the best results from an insecticide.

Flea beetle insecticides do most of their work by contact. Because canola seedlings cover little ground area and flea beetles are small targets, spray quality matters.

The council recommends adequate water volume, with at least 10 gallons per acre as a baseline. Higher water volumes, in the range of 15 to 20 gallons per acre, may improve results when striped flea beetles are common or when conditions push beetles lower on the plant.

Nozzle choice should also be checked against the product labels. The council says many flea beetle insecticides call for medium nozzles, which can offer a compromise between coverage and drift reduction.

While the practice could be a valuable time saver, there are a couple of caveats to consider before pulling the trigger.

Growers will need to confirm that the tank mix is allowed under current label rules.

The Pesticides Regulatory Directorate, formerly called the Pest Management Regulatory Agency, updated its tank-mix labelling guidance in January 2025, so growers should check the latest product labels before adding an insecticide to a herbicide pass. If label directions differ, the most restrictive requirements apply.

Finally, while killing two birds with one stone is tempting, the practice should only be used when the threshold is exceeded. Gavloski noted that farmers need to remember that it is not just flea beetles being affected by these applications.

“Most of the insecticides registered for flea beetles in canola are broad spectrum, and will also kill beneficial insects in the field,” he said.

“Reduced levels of beneficial insects can increase the risk of other insect problems throughout the season.”