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?
Luckily for growers, seed-applied canola insecticide treatments aren’t affected by PMRA’s re-evaluation, meaning when it comes to seed treatments, it’s business as usual. Under heavy feeding pressure, it can seem like seed treatments aren’t doing their job, but recent work from AAFC Saskatoon shows the opposite is true.
They found an 18.6 bu/ac yield reduction in canola plots that were untreated (7.7 to 25.1 bu/ac) compared to those 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 BrettYoung Agronomic and Regulatory Services Manager, Justine Cornelsen.
Some of those best management practices are shallow, uniform seeding depth, targeted plant populations between five to eight plants per sq. ft, and seeding into a warm, moist seedbed. They aid in quick seed germination and growth and help get plants through the susceptible flea beetle feeding window to the 4-leaf stage where they can grow through feeding.
“The best management practice to stay ahead of flea beetles, though, is scouting early on,” Cornelsen added. “Because a few flea beetles can turn into a lot in a matter of a few days, if not hours.”
AAFC research scientist Bob Elliot found insecticides were much more toxic if crucifer flea beetles ingested them rather than topical application (spray hitting flea beetles directly). Many seed treatments were tested on crucifer flea beetles — not striped ones, so it’s important to remember feeding behaviour and preferred weather conditions differ between species.
The decision of using a foliar insecticide is not an easy one — it can be a time consuming application that kills off beneficial insects. So, when deciding to use it, one of the first things you should consider is if the feeding damage has reached the action threshold of 25% leaf defoliation.
Actively scouting the fields to measure feeding damage, assessing stem feeding damage, and looking at the plant population and forecast will help you to make the insecticide spray decision. Fields with higher plant populations can lose several plants to flea beetles and still be able to achieve targeted yield potential. Fields with less than 5 plants per sq. ft run the risk of losing plants and not having enough left to maximize yield.
You should also consider crop stage on the remaining plant population as the susceptible window for flea beetle feeding damage is cotyledon to the 4-leaf stage. After the 4-leaf stage, the plant is typically able to outgrow the feeding damage but if the weather isn’t ideal for plant growth and the plants stall out before that stage, an insecticide application 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.
There are several insecticide options that offer control of flea beetles in canola, the pyrethroids, carbamates, and organophosphates. The most common insecticides used are ones in the pyrethroid class, which is where lambda-cyhalothrin active products reside. Thankfully, there are many other options still available to growers, two of which are Decis® and Pounce®.
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.”
If spraying, only use pesticides registered for flea beetles in canola. Check labels. Labels for lambda-cyhalothrin products will be changing this year.