Flea beetles are spotty throughout the Prairies this season, but spotting them and establishing when to treat for the insects can be challenging.
The tiny insects are reported in central and northwestern Manitoba, east, central and northern Saskatchewan and central Alberta near Fort Saskatchewan and Redwater.
While many crops have outgrown the risk of significant damage, later seeded canola crops are still at risk.
While most of the populations are being found on volunteer canola and wild mustard, the beetles are finding their ways into fields where seed treatments weren’t used or are in short rotation or on continuously cropped land.
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A proper assessment of flea beetle damage needs to be made to ensure that spraying is warranted.
Jim Bessel of the Canola Council of Canada said seed treatment to avoid the problem in the first place is the best course of action.
However, if the timing for seed-applied insecticide is expiring, damage is increasing or crop emergence was delayed due to deep seeding depths or cool weather, then producers can also find themselves applying foliar insecticides.
“If you’ve got the bugs and they’re doing a lot of damage then you need to be aware of your options,” Bessel said.
Provided seeding rates and emergence of the crop were average or better there should be enough plants with enough leaves to sacrifice a few to the insects.
“A few holes in the leaves isn’t a big issue and you should take into account plant stress due to drought or heat as well, but that isn’t much of an issue this year,” he said.
“Canola seedlings can stand a 50 percent leaf loss and still produce an average plant, but by the time you can treat for them they will have done more damage than that if you wait to see 50 percent losses,” he said.
When 25 percent defoliation is found, then producers should consider treating immediately.
Bessel said producers should examine their crop carefully. Flea beetles can travel in calm, hot, dry conditions, but in moist windy seasons they are limited in their movements.
If the beetles are only found in the crop edges, then producers can apply foliar sprays in those areas only, saving application money and time. Another downside of treating is the damage the insecticide will do to beneficial bugs already in the field.
Diadegma insular is thought to be a major predator of diamondback moth larvae. Foliar applications of insecticide will wipe out these and other beneficial insects living in the fields and leave the plants more vulnerable to later maturing bugs like the diamondback moth.
The canola council recommends daily monitoring of the crops in their earliest stages. Scout in the late morning when temperatures exceed 14 C for two full weeks after emergence.
Slough edges and crop borders are often more vulnerable than interiors of the fields, but random samples across the field should be taken.
