Flea beetles are easily the most chronically damaging insect pest in western Canadian canola. Damage results in yield losses estimated at $300 million each year. To limit damage, experts recommend acting early when an average level of defoliation level of 25 per cent or more is reached.
Early action necessary
According to Greg Sekulic, an agronomy specialist in the Peace region of Alberta, flea beetles are most damaging at emergence during the true leaf and cotyledon stage. For this reason, the first line of defense in protection against the destructive pest is a seed treatment, said Sekulic in a recent interview. Growers can recover without any negative impact on maturity or yield when 50 per cent of the cotyledon leaf area remains. But because flea beetles move quickly, the recommended economic threshold is 25 per cent damage.
Sekulic recommends that growers regularly scout emerging canola fields. There are a few guides on the Canola Council of Canada’s website that show growers what crop damage looks like at different stages. They should help determine the right time for a foliar insecticide application. “Anything registered is good to go,” said Sekulic. “Just make sure you stay on labeled rates.”
Over the past 30 years, the crop protection industry has spent and incredible amount of time and money trying to build forecasting models for flea beetle pressure, all of which have failed to predict specific regions, let alone individual fields that would be at risk. “Due to the variable nature their ecology, it’s really difficult to predict with any certainty where they’re going to be in higher numbers in spring,” said Sekulic.
Sekulic says that he used to advise growers to scout in the fall and plan spring management based on what they saw. “Now we don’t anymore,” he said. “We basically just advise that if you grow canola, an insecticidal seed treatment is far and away the safest means of protecting against flea beetle simply because we cannot predict where they’re going to emerge at all.”
With the understanding that the use of insecticides increases production costs, environmental risk, and the potential for increased selection pressure for insecticide-resistant flea beetles, researchers are looking to possible new management strategies. The hope is that a better understanding of effective predators in major Canadian canola growing regions may allow natural enemies to be included in the economic threshold recommendation. This could, in turn, reduce the incidence of over-spraying and the possibility of increased selection pressure.
As part of a project funded by Agriculture and Agri-Food Canada, Alejandro Costamagna, assistant professor in the Department of Entomology at the University of Manitoba, and a team of researchers have been looking into the natural enemies of flea beetles. They’ve developed DNA primers that are able to detect flea beetle DNA in their predators’ guts. The problem is that, since they’re very mobile, flea beetles are difficult to catch for both humans and predators. The researchers are in the process of testing the insects and will continue to process insects from the fields next year. Predators include ground beetles and spiders, some of which they think also feed on larvae and eggs in the soil. Again, this is very difficult for the researchers to monitor.
The other part of their research, said Costamagna, is examining landscape characteristics that could potentially limit flea beetle populations. “The rationale is that if you have non-crop habitats — natural habitats — those will harbour good, sustainable populations of natural enemies and those will help to control the flea beetles,” said Costamagna.
“For every field we sample, we map the landscape around it,” he continued. “We look at crops and habitats up to two to three kilometres around it and then we quantify a lot characteristics in that landscape.”
Costamagna said that while they have several fields in four major regions in Manitoba, Saskatchewan and Alberta, there is always a need for more. Producers who want to participate in the research project should contact Costamagna directly at [email protected]
Economic threshold trials are also being conducted, but it’s too early to report on the results. For now, the best course of action is to stick with the 25 per cent economic action threshold recommendation.
This article first appeared in the May 16, 2017 issue of Grainews.