Cover crops may replicate zero till for flea beetle control

When it comes to flea beetles, there are no easy answers.

When a canola crop grows slowly and beetle populations are high enough, the pest can quickly devastate a canola field and force a grower to reseed.

But earlier this month, a posting on Twitter mentioned a simple fix to flea beetles — cover crops.

“Someone … (said) this week how canola seeded into a rye cover crop was hardly touched by flea beetles, compared to that in tilled fields,” Manitoba Agriculture said in its June 9 crop pest report.

No studies or research have been done on cover crops and if they impede the insect pest, but scientists have looked at zero tillage and what it means for flea beetle pressure in canola.

In the late 1990s, Lloyd Dosdall, an entomologist with the Alberta Environmental Centre in Vegreville and then professor at the University of Alberta, conducted a study on seeding rates, row spacing, zero till and other practices that might hinder flea beetles.

“They had zero-till plots and conventional till plots. In that study, their conclusion was … less flea beetle feeding in the zero till plots,” said John Gavloski, an extension entomologist with Manitoba Agriculture.

Researchers in North Dakota and Sweden have reached a similar conclusion. Reduced tillage and seeding canola directly into stubble seem to impair flea beetle feeding and densities.

“You are making the climate for flea beetles a bit less attractive,” Gavloski said, adding the beetles prefer warmer environments with bright sunlight.

As well, in a dry spring, the stubble and trash on a zero-till field would retain more moisture in the soil. That should spur canola development so that the plants grow quickly and reach the point where they can tolerate bites from the beetles.

“One of the reasons that people have to do foliar sprays (for flea beetles) … is because it takes too long to get from the day of seeding to the three or four leaf stage,” Gavloski said.

Based on the research, direct seeding into a zero-till field should reduce flea beetle damage, but it will not eliminate the problem, Gavloski said.

A terminated cover crop could perform the same function as crop stubble, but it’s hard to know because it hasn’t been studied.

“We don’t have the research to say … that a Twitter picture (of canola seeded in a cover crop) is a reliable recommendation,” said Keith Gabert, an agronomy specialist with the Canola Council of Canada in Innisfail, Alta.

“But it’s a good discussion to have.”

Every spring, Gabert gets calls from dozens of farmers who have problems with flea beetles.

On the rare occasion, a massive population of beetles will damage a field with a healthy stand of canola.

Most of the time, flea beetles take advantage of poor growing conditions.

“Flea beetles tend to become worse when there are other problems in the field,” Gabert said.

“Something is wrong with your crop. You have soil crusting so you have less plants. You have drought, you have frost. You have hot temperatures a week after frost.”

In some years, having black soil can help with crop emergence and rapid canola growth.

“But if you ever run into conditions where moisture retention is important … then the zero-till fields pull ahead,” Gabert said.

“Whatever practices would help a grower get a rapidly established canola crop would probably be the ones that help them manage flea beetles.”