Canola School: Catch the early signs of flea beetles

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Seeding is well under way across the Prairies and as farmers start seeding canola, flea beetles are likely the biggest pest of concern.

For this Canola School, correspondent Kara Oosterhuis sits down with Dr. John Gavloski, the provincial entomologist with Manitoba Agriculture and Resource Development.

Even if canola isn’t in the ground yet and as seeding progresses, early flea beetle feeding damage can be found in Brassica weeds. “If you want to check out what the population’s like, if you know if there’s a field that has some volunteer canola that’s up, go have a look at that, you’ll probably see shot holes in it, you’ll probably see some flea beetles on it.” Gavloski advises. Volunteer canola, wild mustard, and other cruciferous weeds will be target by flea beetle first.

“Flea beetles are most active when it’s calm, warm, and not too humid.” says Gavlovski, “Those are the conditions that they really like.”

Striped flea beetle tend to come out first in most areas of the southern Prairies. However, there’s another species, the crucifer flea beetle, that are all black and come out later in the season. Research is currently being conducted on the differences between striped and crucifer flea beetles in terms of feeding damage, whether a species feeds more on stems or on leaves.

So what can producers do to mitigate flea beetle injury or to get ahead of them? Gavloski says to try to shorten the interval between the time of seeding and the three to four leaf stage. When that early growth goes beyond the three weeks of seed treatment insecticide control, problems may arise. Seeding a bit shallower may also help, so that the crop comes up quickly but that will depend on soil moisture.
(Watch the full interview between Kara Oosterhuis and Dr. John Gavloski below)

For an economic threshold for making a spray decision, roughly 25 per cent of the cotyledon and early true leaf surface would be defoliated or damaged. Flea beetles make small little pits or shot holes in the cotyledons, which eventually turn brown, dry up, and holes are created. It’s natural to overrate how much damage has occurred, says Gavloski, but things can jump from 25 per cent to a lot more, very quickly if there’s warm, calm weather he warns. By June, flea beetle populations may start to die out, so make sure they’re still present.

Begin by scouting edges of fields. Flea beetles will travel by walking, and are more likely to be found in the edges of fields when temperatures are at about 15 degrees celsius. Flea beetles spread by actively flying once temperatures are above the 15 degree mark.

As far as how severe damage can be from flea beetles, it can be as bad as a field having to be reseeded Gavloski says, and scouting is crucial to catching this early. Gavloski hasn’t identified any flea beetle hotspots in Manitoba as of yet, but says that as more canola acres get seeded across the province, more flea beetle damage will become apparent.

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