Cereal leaf beetle is starting to show up in some fields in Ontario. A few locations tend to experience a higher frequency of infestations including fields near Dresden, Bolton, Stayner, Seaforth, and Clinton. But this does not mean that other fields in Ontario are not at risk.
Cereal leaf beetle (CLB) adults are beetles with metallic blue-green wings and a reddish-orange head and legs. The larvae appear black in colour as they are covered in their own fecal material to stay moist. When this outer coating is removed, you will find a yellowish larva underneath. A good indication that you have CLB in your field is if you find black streaks across your pant legs after walking through the field. I am sure you can figure out what that really is (Yuck!)
Both adults and larvae chew long strips of tissue between the leaf veins. This creates a window-paning or “skeletonizing” effect. Heavily damaged fields appear silver. Most of the damage is done by the larvae in June but can start as early as May.
Examine 20 plants in five locations across the field. It is important to scout various areas of the field, as CLB tends to be unevenly distributed across the field. Record the number of beetles and larvae found per plant and the crop stage. Scout every 5 days, as damage can increase dramatically within days.
Control is warranted if an average of 3 larvae per tiller are found before boot stage. After boot stage but prior to heading, one CLB adult or larvae per stem warrants control. If significant feeding is taking place on the flag leaf in the early heading stages, control may be warranted but make sure that CLB is still present and actively feeding in the field before deciding to spray.
Only use foliar insecticides when thresholds have been reached and pay close attention to pre-harvest intervals. Natural enemies, particularly parastioids are highly effective at controlling this pest and can be negatively impacted from insecticide sprays which could lead to frequent outbreaks for several year after application. Clean plowing also increases the risk of this pest, because the overwintering sites of the parasites are destroyed.