To spray or not to spray: managing flea beetle pressure

Category: Grow Grain

Just because your neighbour is spraying doesn’t mean you have to spray too. Here’s how to assess flea beetle pressure so you can make a smart spray decision.

Flea beetles on canola cotyledons.

We’re seeing signs that flea beetles are feeding on canola on the prairies. It’s worrying farmers whose plants have already experienced stress from frost and/or dry conditions. I know it feels like we’re fighting one problem after another, but I want to encourage you to take a step back. Assess your field before rushing in with an insecticide. Just because you see the odd flea beetle doesn’t mean you’re going to lose the crop, and just because your neighbour is spraying doesn’t meant you have to spray too. Your canola plants can handle a few nibbles on their cotyledons. Here’s how to assess flea beetle pressure so you can make a smart spray decision.

A few bites are normal

Flea beetles are always a threat, and they’re more prevalent this year. While including an insecticide in your seed treatment protects the crop during emergence, that protection wears off after three or four weeks. If your canola has been in the ground for over a month, you may see signs that flea beetles have been chewing on your crop. 

In order for your seed treatment to control flea beetles, they need to feed on the plant. It’s normal to see a few bites taken out of the leaves and cotyledons.

As long as the true leaf is intact, and you have good growing conditions and an otherwise healthy crop, your canola plants can outcompete the pests.

Intact true leaves on canola plants despite flea beetle pressure.

Check 10 spots in your field to get the full picture

I recommend scouting 10 different locations in your field to determine your field-wide average. Flea beetles overwinter in ditches and tree lines, so the perimeter will see the most pressure. If you go further into the field, you may not see any signs of flea beetle damage. Take all these locations into account when making your spray decision.

Flea beetles like warm temperatures and calm winds. If you’ve had cool windy weather, the bugs will move to the underside of the leaf or cotyledon for protection. When they’re down there, they might feed on the stem. Stem feeding is going to bring your threshold level down faster than leaf feeding. If it’s just a nibble, the plant can recover. If there’s a large chunk missing, you should consider that plant as lost.

Four canola plants/sq. ft. is all you need for a good yield

Assess your plant stand when making a spray decision. We typically seed to have 7-10 plants per square foot at emergence. At that rate, you can afford to lose a plant or two to flea beetles. As long as you’re above four plants per square foot, you’re going to get a good yielding crop.

Severe flea beetle damage to canola plant.

Wait until you’ve reached your economic threshold

Panic spraying is hard on the biodiversity in your field because insecticides harm non-destructive insects too. Putting out more money for crop inputs also cuts into your ROI. Hold off on spraying until you’ve reached the economic threshold – where leaving the beetles unchecked will cost you more than the insecticide investment.

If you see an average of 25% damage to the leaves, you likely need an in-crop application. 

I recommend a product like Decis® or Matador®. If you’ve made a proper assessment and know that spraying is warranted, these products provide good control of flea beetles in canola. If possible, spray just the outside perimeter of your field along ditches and tree lines where flea beetle pressure is greatest.

For help assessing flea beetle pressure and deciding whether to spray, contact your local Cargill location.

 

Decis® is a registered trademark of Bayer CropScience. Matador® is a registered trademark of a Syngenta group company. 

Tags: Agronomy, Insecticide, Crop Protection, Pests, Canola

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