Weather can make flea beetle predictions tricky

High numbers of flea beetles in the fall are a good indicator for high populations the following spring, but weather conditions will also play a major role.

“If you have lots (of flea beetles) in the fall, there’s a strong chance of problems in the spring, if it’s warm and dry,” said Julie Soroka, an Agriculture Canada research scientist in Saskatoon.

However, she said warm, dry, and calm weather will allow the highly mobile bugs to migrate into fields in the spring even if the population was low in the fall.

The importance of such an uncertain variable makes it difficult to plan control strategies, but the stakes are high.

Soroka and Agriculture Canada researcher Bob Elliott recently wrote in a journal article that flea beetles may be responsible for as much as 10 percent of annual production losses in North American oilseed brassica crops. The losses are estimated to cost more than $300 million a year.

Soroka said flea beetles are hardy and have few natural predators. Control strategies for the pests are mainly chemical.

Seed treatments provide the first line of defence, and individual producers must gauge whether populations they see in the fall are worth the extra cost of going to a higher-grade seed treatment or increasing seeding rates.

“If you don’t see them in the fall, use a low rate. Don’t use the max rate unless you need it because you are really setting the stage for resistance,” said Soroka.

Foliar insecticides may become necessary if flea beetles have damaged more than 25 percent of the plants’ leaf surface, according to the journal article.

In most cases, flea beetles start consuming canola at the edges of a field and work their way in, which means foliar treatment can sometimes be limited to a field’s outer edges, she said.

However, she encouraged producers to thoroughly scout their fields before treating because there is no guarantee this will always be the case.

“There’s a lot we still don’t know about these beasts,” she said.

Soroka said other management practices can also be used alongside chemicals, such as planting for early emergence, into tall stubble and at a high seed rate.

She said the cooler microclimate created by no-till agriculture gives that cropping system a distinct advantage over conventional tillage when controlling flea beetles, which might even be comparable to chemical treatments.

Soroka said good field scouting in fall and spring is vital.

As well, producers on the southern Prairies may want to look for flea beetles a few weeks earlier in the spring because there are preliminary indications that the crucifer species of flea beetle common to the region is being displaced by striped flea beetles common in northern areas.

Soroka said this is likely because of the striped beetles’ higher tolerance to neonicotinoid chemicals used in seed treatments and insecticides.

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