The Canola Council of Canada's 2024 grower survey asked growers to identify the diseases, weeds, and insects posing the greatest economic risk to the crop. Flea beetles topped the list once again, maintaining their position from the 2022 and 2020 surveys.
Despite their persistence, there are strategies to mitigate the risk posed by flea beetles. John Gavloski, an entomologist with Manitoba Agriculture, suggests that canola crops reaching the four-leaf stage within three to four weeks of seeding are less likely to require foliar pesticide sprays. Slow-establishing and non-competitive crops are often the ones needing in-season foliar sprays.
Keith Gabert, an agronomy specialist with the Canola Council of Canada, emphasizes the importance of rapid stand establishment "Canola sown in warm, moist soil will emerge quickly and uniformly, while warm conditions without moisture tend to favor flea beetles over the crop."
Gabert says if they could remove one issue for canola growers, it would be that establishment phase where they're really not that confident that their canola is off to a good start. "Flea beetles are a really important part of that. Unfortunately, we can't predict them, so it leads us to how do we set ourselves up for success and how do we watch to make sure that or at least know if we're not on the path."
Key Areas of Concern: The Peace and Manitoba
The Peace region and southern Manitoba are particularly vulnerable to flea beetles. These areas often face challenges with rapid stand establishment due to varying weather conditions, but any area that has difficult establishment could have flea beetles. Gabert notes, "There's no magic formula on how to manage flea beetles, but you should be monitoring your crop to see it come out of the ground. If you start to see flea beetle activity, those little shot holes, the pitting action that flea beetles have, it's a hint that there may be something going on as your crop comes up."
Economic Threshold and Foliar Insecticide Use
The economic threshold for flea beetle damage is typically around 25 percent defoliation. Gabert advises, "If you've got a lot of feeding, we've got a really nice chart on our website for the amount of defoliation. The challenge is to scale off enough and frequently enough to understand if my crop is looking better every second day. If it's not, then you need to figure it out. If flea beetles are the issue, you might need to consider a foliar insecticide."
Target 5-8 Plants per Square Foot
Canola crops with five to eight plants per square foot typically face minimal risk from flea beetle feeding. More plants mean fewer beetles per plant, which helps keep leaf area loss below the 25 percent threshold.
Seed Shallow into Warm, Moist Soil
Seeding later can reduce flea beetle risk if it leads to warmer soils and faster growth. However, later-established crops may face increased fall frost risk due to flowering on hotter days.
Consider Advanced Seed Treatment
Advanced seed treatments can enhance flea beetle protection in high-risk areas. Gabert notes, "You can buy an upgrade to seed treatment that will have a number of different choices that could improve flea control. However, seed treatments don’t work as well or are not actively taken up when the plant is not growing or when moisture is inadequate for the transfer of active ingredient from seed coat to seedling."
Use Safe Rates of Seed-Placed Fertilizer
It's recommended to use only phosphorus in the seed row and no more than 20 lb./ac. of actual phosphate. Higher rates of seed-placed fertilizer can stress the plants, slow growth, and reduce the stand.
Till versus No-Till
While canola planted in warmer, blackened soil may emerge faster, this same soil can attract more flea beetles. Crop residue retains soil moisture, aiding rapid emergence when moisture is limited.
Gabert advises, "There's no magic formula on how to manage flea beetles, but you should be monitoring your crop to see it come out of the ground. If you start to see flea beetle activity, those little shot holes, the pitting action that flea beetles have, it's a hint that there may be something going on as your crop comes up."
By following these agronomy steps, growers can put their canola crops in the best possible position to withstand flea beetle pressure.