Flea beetles: At-risk crops

June 1, 2016 - Issue 11

Canola fields at greatest risk from flea beetles — therefore fields most likely to need a spray — tend to be those seeded early and that went through a long stretch of slow growth. These early fields attracted flea beetles, which also emerged early this year, looking for something to eat. Slow growth used up the protection period for seed treatments, leaving crops vulnerable before they could outgrow the threat.

Crucifer and striped flea beetles are feeding together in this crop. Credit: Brent Wiebe

Crucifer and striped flea beetles are feeding together in this crop. Credit: Brent Wiebe

Check all fields, but especially those that may be in this situation. Use this checklist to help decide whether to spray.

During cool periods that may have caused slow growth, flea beetles will also take cover — feeding on stems and the underside of leaves. Stem feeding, if common throughout a field, may have a lower control threshold than the 25% leaf area loss for leaf feeding.

Good moisture and warm weather over the next week should result in rapid crop growth. This could help reduce the impact from flea beetle feeding, but note that warm weather will also make the flea beetles more active. They may also feed through warm nights.

Product rotation. Some fields sprayed once for flea beetles may need to be sprayed again in rare situations. In that case, note that some products have restrictions on multiple applications and total rates for the year. Check product labels.

Adding insecticide to herbicide. When spraying for weeds it can be relatively low cost to add an insecticide. However applying insecticides without regard for thresholds is not a recommended practice. One reason is the unnecessary damage it can cause to beneficial insect populations. Another is that many insecticide can only be sprayed once per year. By needlessly spraying for flea beetles you lose the ability to use that product later in the season if you need it for another pest. Read more.

Further reading:

Estimating flea beetle damage in canola
Prairie Pest Monitoring Network blog

Canola Watch