There have been many reports of cereal leaf beetle adult activity over the last few weeks. Adults do some feeding but also lay eggs that give rise to the real issue – cereal leaf beetle larvae. Eggs will be hatching within the next week or so. With daily growing degree days accumulating more quickly than usual, the populations and feeding activity could catch us off guard. A few locations tend to experience a higher frequency of infestations including fields near Dresden, Bolton, Stayner, Seaforth, and Clinton but reports from other locations with significant adult activity have come in this year. Stay vigilant and monitor fields over the next three weeks in particular.
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.
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.
Thresholds: If an average of three larvae per tiller are found before boot stage, spray is warranted. One CLB adult or larvae per stem warrants control after boot but prior to heading. If significant feeding is taking place on the flag leaf in the early heading stages, control may be warranted. Only use foliar insecticides when thresholds have been reached and pay close attention to pre-harvest intervals.
BTW- While scouting, keep an eye out for armyworm as well. I expect they will start to show up around the same time. Cool Aprils tend to give rise to armyworm outbreaks.