A large population combined with late podding equals a second chance for canola’s greatest enemy.
However, research indicates agronomy may be able to solve late season flea beetle damage.
When it comes to canola pests, none is more damaging than the tiny flea beetle, and western Canadian producers had their fill of them this year.
“It was a long season of flea beetles,” said Manitoba entomologist John Gavloski.
“The cold weather held the crop back and plants didn’t get the chance to grow past the heavily susceptible stage.”
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At the same time as the oilseed was struggling to germinate and move past the seedling stage, the seed treatment that was supposed to give the canola a fighting chance was beginning to fail as it passed its best-before date.
The late crop was left to survive the first wave of overwintered bugs if producers didn’t intervene with pesticide applications.
As farmers watched their crops develop, many noticed that flea beetle damage continued to cause problems, in some cases all the way into September as the second wave reached maturity and took over where their parents had left off.
Julie Soroka of Agriculture Canada in Saskatoon, who has spent the past three years looking at late season flea beetle damage, said it can be a significant problem.
Her research was designed to measure the threat and establish damage and population thresholds for pesticide application.
In 2006 and 2007, high July temperatures brought the crop to rapid maturity, getting it past the point where the insects could damage yields.
In 2008, canola matured slowly and infestations occurred when the crop was still shifting from green to brown and subject to heavy damage.
Soroka’s field trials monitored late season flea beetle infestations on canola in open and caged crops and with two cultivars.
Two seeding dates were assessed: mid-May and early June.
She said three scenarios were compared:
- Open plots were infested by natural late season flea beetle populations and half of each plot was sprayed with insecticide and half left untreated.
* Metre wide cube cages were placed over early and late crops and infested in early August with up to 26,000 beetles.
- Individual canola plants were sleeved and infested with 100 beetles.
Soroka found that in every scenario, early seeded canola didn’t lose any seed size or yield, and pesticide spraying had no impact on either measure.
In later seeded crops, researchers found that damage could be economically significant if the crop still contained green pods at the time of a large infestation.
Beyond damage
A crop is safe from damage when it passes the 5.2 growth stage with green seeds still present in lower pods.
“Even at 5.1 to 5.2, more than 100 insects per plant in some cultivars and up to 350 beetles in others are necessary to cause significant yield reductions,” she said.
A chemical applicaton would likely pay at those levels, depending on the price, the expected yield of the crop and its price.
Part of the research project polled 130 farmers in Western Canada and one American state about their attitudes toward late season damage by flea beetles.
Nearly all felt there was little or no threat from late season feeding.
They also felt control at that time of year would be difficult because of competing farm activities such as harvest.
Soroka said while the threat is limited to specific circumstances, early seeding avoids the problem.
Derwyn Hammond of the Canola Council of Canada said many producers reported high beetle populations feeding on green canola late in 2009, but the larger threat from these will likely come in 2010.
Significant problems next spring can be avoided by implementing rotations of nonsusceptible crops and longer duration seed treatments and seeding when soil temperatures are correct for rapid emergence.
