Flea Beetles in Canola taking a Bite out of Stands

Many growers are frustrated by trying to control the high populations of flea beetles this season. Some have sprayed for control only to see high populations reappear several days later. Although flea beetles are most active under warm sunny conditions, moisture generally favours insect development. It is important to not spray too soon. Expect to see some feeding damage, as flea beetles must take a bite to die from seed treatment and won’t protect canola from a re-infestation.

flea beetle
A crucifer flea beetle (Phyllotreta cruciferae,
Goeze) feeding on canola. Click image to enlarge.

 Spray Decision Guide

  • Control is generally warranted when there is 25% of the surface leaf area damaged.  The economic threshold is 50% defoliation but intense feeding can quickly take 25% damage to 50%, so 25% is used as the action level. Early application won’t protect a field from re-infestation.  Flea beetles are strong fliers and can quickly re-infest a field.
intesnse feeding by the crucifer flea beetle causing approximately 25% damage
intense feeding by the crucifer flea beetle causing approximately 25% damage. Click image to enlarge.

Check new growth for feeding.  Although seed treatments can provide up to 3-4 weeks control, don’t let your guard down if flea beetles are overtaking new growth. It is important to check newly emerging leaves for damage as damage to the growing point can affect crop development.  Cotyledons can withstand higher feeding levels if the new leaves are unaffected, but action may be necessary sooner if newly emerging growth is being eaten.

  • Assess the health of canola stand. Thin stands with 5 plants/sq. ft. or less or unthrifty stands struggling from seedling diseases, or saturated soils will require watching closely and taking action sooner to protect the population present. On the other hand a healthy stand can sustain higher populations and often can ‘out-grow’ feeding damage.
  • Expect Feeding to last several weeks.  Flea beetles emerge from overwintering sites for several weeks and may continue to feed into early July before dying off.
  • Watch Field Margins. Flea beetles first migrate in from fencerows and wooded areas to field margins, so populations are highest in this area. At this time of year however flea beetles can fly into fields especially on warm, sunny days creating hot spots in a field.
  • Striped Flea Beetles are harder to control.  There are several types of flea beetles, with the striped flea beetle being the most aggressive feeding type and difficult to control.  Fortunately most of the flea beetle types being found this season are not striped.  
  • Application tips.  Insecticides provide contact activity so control will be highest during the warmest, sunniest periods of the day when beetles are most actively feeding. On cool cloudy or windy days, beetles stay closer to the ground feeding on underside of leaves or stem. It is critical to achieve good product coverage by using appropriate size nozzle providing medium droplet size and good water volume 65 l/ac (15 gal/ac). If you need to spray more than once try to change to a different product to reduce change of resistance developing.
  • Registered products include Silencer, Matador, Decis, and Sevin XLR Plus.  Decis has a small repellence effect which may be slightly more effective.
  • Protect Honey Bees.  Avoid applying insecticides if bees are actively feeding. Be conscious that flowering weeds in fencerows or in the field will be attractive to bees. Before applying a pesticide, advise local beekeepers so they can move colonies out of the danger area. Contact the Provincial Apiarist at 1-888-466-2372 ext. 6-3595 for a list of the beekeepers in the area or click here for a list of provincial bee inspectors who know the local beekeepers.