Newly regulated changes to certain insecticides in Western Canada could give flea beetles the upper hand this growing season.
The Pest Management Regulatory Agency (PMRA) recently re-evaluated certain lambda-cyhalothrin products, causing manufacturers of the product to re-evaluate their labels, at least for the 2023 season. PMRA’s decision is causing some formulations, like the common Matador® and Silencer® labels, to not be available for use this year in crops like canola that might be fed to livestock.
With these changes giving flea beetles a possible advantage this season, how can we protect our canola from them?
Seed Treatments
Luckily for growers, seed-applied canola insecticide treatments are not affected by PMRA’s re-evaluation. For seed treatments, it remains business as usual.
Under heavy feeding pressure, it can appear as though seed treatments are underperforming, but recent AAFC Saskatoon results show the opposite.
What the Research Shows
AAFC found an 18.6 bu/ac yield reduction in untreated canola plots (7.7 to 25.1 bu/ac) compared to plots treated with a neonicotinoid seed treatment (27.8 to 49.9 bu/ac).
“Using an enhanced insecticide seed treatment like Fortenza® Advanced or BUTEO® start in combination with other best management practices helps relieve flea beetle feeding stress,” said Justine Cornelsen.
Best Management Practices That Support Seed Treatments
These practices help seeds germinate quickly and grow through the susceptible feeding window:
- Shallow, uniform seeding depth
- Targeted plant populations of 5 to 8 plants per sq. ft
- Seeding into a warm, moist seedbed
“The best management practice to stay ahead of flea beetles, though, is scouting early on,” Cornelsen added. “A few flea beetles can turn into a lot in a matter of a few days, if not hours.”
Additional Research Insight
AAFC research scientist Bob Elliot found:
- Insecticides were more toxic when ingested by crucifer flea beetles rather than by topical exposure.
- Many seed treatments were tested on crucifer flea beetles, not striped beetles — and these species differ in feeding behaviour and preferred weather conditions.
Foliar Controls
Using a foliar insecticide is a significant decision. It can be time-consuming and may kill beneficial insects, so the first question to ask is whether feeding damage has reached the 25% leaf defoliation threshold.
Factors to Assess Before Spraying
- Measured feeding damage (leaf and stem)
- Plant population
- Weather forecast
- Growth stage
Fields with higher plant populations can tolerate some plant loss. Fields below 5 plants per sq. ft are more vulnerable to yield reduction.
Why Crop Stage Matters
The susceptible window for flea beetle feeding is cotyledon to the 4-leaf stage. After the 4-leaf stage, canola typically outgrows feeding damage. However, if poor weather stalls plant growth before that stage, foliar sprays may be required.
“Plant stresses that slow canola growth in the seedling stage put an increased risk of needing foliar insecticides,” said John Gavloski, Entomologist with Manitoba Agriculture.
Foliar Options Still Available
Several insecticide groups remain available for flea beetle control in canola:
- Pyrethroids
- Carbamates
- Organophosphates
The most commonly used are pyrethroids, including products containing lambda-cyhalothrin. Even with label changes, growers still have other effective options.
Tips for Effective Foliar Application
Gavloski recommends:
- Using threshold-based decisions
- Considering spot spraying or edge spraying
- Watching the weather, as temperature affects pyrethroid performance
For example, the Decis® label states:
“Do not spray under a strong temperature inversion or when temperature exceeds 25°C as this will result in a reduction in control. Best control will be achieved when deltamethrin is applied during cooler periods of the day.”
Options for Foliar Control of Flea Beetles
- Decis: Provides fast, effective control of many insects in many crops and is labelled for control of flea beetles.
- Pounce®: Is a top-performing solution for control of both striped and crucifer flea beetles in canola.
To use foliar insecticides efficiently, Gavloski said to use existing thresholds to make the spray decision. He recommends assessing if spot spraying or edge-spraying is an option but also keeping an eye on the weather as some pyrethroids are more toxic at lower temperatures to the flea beetle.
The label for pyrethroid Decis (active ingredient deltamethrin), for example, says:
“DO NOT spray under a strong temperature inversion, or when temperature exceeds 25°C as this will result in a reduction in control. Best control will be achieved when deltamethrin is applied during cooler periods of the day.”
Key Reminders When Spraying for Flea Beetles
- Use only registered products: Always use pesticides registered for flea beetles in canola, always check labels.
- Expect label changes: Be aware that labels for lambda-cyhalothrin products will be changing this year.
FAQ
What recent changes have occurred in insecticide regulations for canola crops?
The Pest Management Regulatory Agency has re-evaluated certain lambda-cyhalothrin products, causing common products like Matador and Silencer to not be available for use on canola fed to livestock for the 2023 season.
Are seed treatments affected by the new insecticide regulations?
Seed-applied canola insecticide treatments are not affected by the recent re-evaluation so growers can continue using them as before.
How effective are insecticide seed treatments against flea beetles in canola?
Research from AAFC Saskatoon found that untreated canola plots had a significant yield reduction compared to those with neonicotinoid seed treatment, showing that seed treatments help relieve flea beetle feeding stress.
What best management practices can help reduce flea beetle damage?
Practices like shallow, uniform seeding depth, maintaining plant populations of five to eight plants per square foot, seeding into a warm moist seedbed and early scouting can help get plants through the susceptible feeding window and minimize damage.
When should foliar insecticides be considered for flea beetle control?
Foliar insecticides should be considered if feeding damage has reached the action threshold of 25 percent leaf defoliation or if weather conditions slow plant growth and put seedlings at greater risk.
What foliar insecticide options are still available for controlling flea beetles in canola?
Growers can still use pyrethroids such as Decis and Pounce as well as carbamates and organophosphates for foliar control of flea beetles in canola.
What factors should be considered when applying foliar insecticides for flea beetle control?
Decisions should be based on field scouting, plant population, crop stage, forecast conditions and label instructions, such as temperature restrictions for products like Decis.
