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Flea beetles threw a curve this season

Managing flea beetles threw traditional wisdom out the window in 2019. What does this mean for the next growing season?

 

Canadian farmers have had to contend with flea beetles for as long as they’ve been growing canola. This year they appeared early and damage was generally heavier than anticipated. The beetles often wreaked havoc in unexpected areas, while regions that saw heavy adult populations the previous fall had relatively little damage.

As often seems to be the case with flea beetles, growers could expect the unexpected.

“We’ve been talking about flea beetles for as long as I can remember, however things have changed in recent years,” says Ted Labun, Seedcare technical lead for Syngenta Canada. “There has been more discussion about how to best protect against them. The growing season has been longer and drier just about everywhere. This year in particular that created a lot of variability in emergence and a noticeably lower-than-optimal plant stand, which allowed for extended feeding for the beetles.”

Since flea beetles are hardy and easily overwinter, they are ready to start feeding as soon as conditions allow. When they feed on canola, emergence is uneven, plant stand is thin and overall development is delayed with uneven maturity. Damage from feeding can also provide a vector for disease later in the season.

“This year, some growers who seeded early, as is usually recommended for canola, ended up with some trouble this season,” says James Tansey, provincial pest management specialist with the Saskatchewan Ministry of Agriculture. “It was generally cold and dry throughout some parts of the Prairies so the seed stayed in the ground or grew slowly and was unable to get the full benefit of the seed dressing. The flea beetles came in and were able to take advantage of these conditions.”

Growers were often able to address early damage with foliar control, but the cost- and resource-intensive option isn’t something they would choose every year. Foliar applications are generally recommended at a 25 per cent defoliation action threshold. While this year’s delayed spring with its late frost and widespread lack of moisture was unusual, where it hit was unpredictable.

“In western Manitoba we saw a lot of overspraying this year because the flea beetles were in greater numbers than the seed treatment could manage,” says Gregory Sekulic, an agronomy specialist with the Canola Council of Canada. “In southern Alberta, we saw more feeding than usual, with varying amounts of foliar control required. Whereas in the Peace region there was actually less flea beetle activity than we usually see.”

Because of the delayed emergence, canola also grew unevenly. Canola is traditionally a very ‘plastic’ crop and can adapt to different growing conditions. While early indications for this year’s crop are still positive, yield gains were achieved under challenging conditions.

“Canola is a resilient crop,” says Labun. “If it survives it can compensate for a lot of that early damage but it will take a hit. It doesn’t take long for the damage to approach the seedling threshold that requires a foliar insecticide, and canola responds very well to those products as long as you get it by that four-leaf stage. But that timing can be the tricky part for growers who are ready to apply their herbicide around that time as well.”

ADDITIONAL PROTECTION

Labun says early-season protection from seed treatment should be the goal, and most years it is effective. All hybrid canola is purchased with a foundation seed treatment applied, but growers can choose to add additional insecticide or fungicide products for more robust protection. “It really helps with the overall resilience of the plant if you can keep the seed protected for those first three to four weeks until the plant stand is established,” he says.

For enhanced protection, growers can choose a seed treatment such as Fortenza Advanced to help support stand establishment and protect their investment into high-value seed genetics. “Growers never used to have a choice in what went on their seed,” Labun says. “Now growers can discuss with their retailer the concerns they have and make the decision when they purchase their seed as to how to best protect their investment.”

Fortenza Advanced is a new seed treatment available for commercially treated canola for the 2020 growing season. It is a combination of Group 4C and Group 28 insecticides, providing protection on both striped and crucifer beetles. The two active ingredients mean growers are less likely to need a foliar insecticide. Fortenza Advanced also provides cutworm control.

Tansey agrees that a seed treatment is ideally the best way to tackle flea beetles and in most years, a good seed treatment package combined with solid agronomics will keep damage to a minimum. While foliar insecticides are an excellent rescue tool, Tansey recommends caution. “It’s important to note flea beetle activity and crop stage: if there are no active flea beetles or the crop is past the four-leaf stage, control is likely not warranted. You’ll want to avoid ‘revenge’ sprays.”

PREDICTING OUTBREAKS DIFFICULT

While researchers have been studying the correlation between fall and spring flea beetle numbers for years, so far a direct connection between the two hasn’t been determined. Flea beetles are incredibly mobile, so where they start doesn’t always connect to where they might end up. Although they typically move by hopping or walking, they are also capable of miles-long flights.

“This year we had pockets of flea beetle pressure that were very high where we didn’t predict it,” says Sekulic. “But also had some pockets where we had no issues where we expected to see higher insect pressure. We have lots of research projects going trying to forecast populations from one season to the next but at this point we are unable to predict where flea beetle pressure will be the highest the
following year.”

As growers start to make their purchasing decisions for the 2020 season, the only thing they can assume is that flea beetles will be there. It’s a
matter of when and how many.

“While growers are looking at the second flush of flea beetles they are seeing at harvest, we don’t know how much that matters,” says Labun. “We do know that spring growing conditions matter. Additional seed treatments matter. Poor emergence matters. Late spring and frost events matter. Flea beetles will always be there so growers need to focus on the things we know and start things off well to set the stage for a strong growing season.”

MOVEMENT OF THE STRIPED BEETLE

Until a decade ago, virtually all flea beetles on the southern Prairies were crucifer beetles.

Until about 2007, striped beetles were more prevalent in the northern areas.“Ninety per cent of what canola growers saw at that time was a crucifer beetle,” says Ted Labun, Seedcare technical lead for Syngenta Canada.

“But now every area of the Prairies has striped beetles. The beetles cohabitate nicely together in the fall, but they behave differently in the spring.”

Crucifer beetles are uniformly black with a blueish hue. Striped flea beetles have longitudinal yellow stripes on an otherwise black body. Striped beetles arrive one to four weeks earlier than crucifer beetles, emerging five to 11 days after the spring thaw.

“We can explain the southeast migration in two ways,” says Gregory Sekulic, an agronomy specialist with the Canola Council of Canada. “First, the increased acres of canola: we are growing so much more canola that there is a greater number of fields on which they can feed. Also, the products we have been using over the past 20 years have been very effective on the crucifer beetle so we are simply seeing more striped beetles which have been better able to metabolize those products.”

Producers can use sticky card traps to identify the species of flea beetles in their field and likely to overwinter. If they do see striped flea beetles, earlier spring scouting is advised.

A composite photo showing the three types of flea beetle which can damage canola. Striped flea beetles arrive one to four weeks earlier than Crucifer beetles, emerging five to 11 days after the spring thaw. | AAFC PHOTO
 
 

 

 
 

 

 

 

 

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