Flea beetles, those tiny, hungry pests, feed on seedling leaf tissue in your canola fields almost every season. Their feeding on young canola plants causes the most economic damage. Understanding the pest and its lifecycle can help determine when control may be necessary, even if you’ve used a seed treatment.
The two dominant species of flea beetles are the crucifer flea beetle, which is solid black, and the striped flea beetle, which is black with orange stripes on its back. The crucifer tends to be more prevalent south of Highway #1 and the striped north of Highway 1, but the striped flea beetle numbers have been quickly rising in the south according to new findings. What’s more, the striped flea beetle tends to emerge earlier, so higher numbers may be observed in an early seeding year.
Typically, the crucifer species is “hungrier” and will eat more than the striped, but the striped flea beetle is actually more tolerant to insecticidal seed treatments, which is a cause for concern in the future.
Overwintering adults begin to emerge from shelterbelts, grasses and leaf debris in spring once temperatures begin to rise above freezing. These adults feed on volunteer canola or mustard plants until crops are planted. The warmer the temperatures the more active they become, and when temperatures rise over 14 degrees C they will begin to fly and spread quickly. Flea beetles can cause economic losses of 10% or more and contribute to problems such as thin plant stands, delayed development and increased disease susceptibility.
Most canola seed is treated with an insecticide (neonicitinoid’s such as Thiamethoxam or Clothianidin) that can typically protect a plant from flea beetle feeding from emergence to the 3rd leaf stage. Once the plants get to this stage it typically is very easy for them to outgrow any flea beetle damage. There is a newly registered product, Lumiderm, available for the first time this year.
The most critical time to watch is from the cotyledon to 1-leaf stage as this is when young seedling canola is most susceptible to flea beetle damage. The economic threshold is 25% feeding on the plant, but being ready to spray from 15-20% damage is a good idea, though, as flea beetles work fast and can do a lot of damage in a short time. The damage is typically highest in headlands, so even though your headlands have reached economic threshold, check your entire field to see what the damage is at. Sometimes spraying the headlands is all it takes to get good control of flea beetles and saves the money of spraying your entire field.
It’s important to note that seed treatment protection only last so long — a prolonged, cool early season may mean the insecticide protection wanes before the pressure has eased or the crop is big enough to outgrow the feeding damage.
The two main options for controlling flea beetles with foliar chemicals are Decis (deltamethrin) and Matador (lambda cyhalothrin). These two products are pyrethroid insecticides and work by contact and ingestion.