Keep an Eye Out for Cereal Leaf Beetle Larvae

Cereal leaf beetle (CLB) adults have been active and laying eggs over the last month in winter cereals. Though the adult feeding does not cause much injury, expect to start seeing larvae and their leaf feeding start over the next few weeks. My crew just found a few first instar CLB larvae today in one of the YEN sites we are monitoring this year. On the positive side, with this heat, the winter cereals are advancing quickly and may get passed the critical early heading stages, avoiding peak larval feeding. But spring cereals might be at greater risk.

Young cereal leaf beetle larva without its fecal coating on scout's arm.
Young CLB larva without its fecal coating on scout’s arm in YEN site. A. Fournie, OMAFRA.

Cereal leaf beetle larvae are 6 mm (1/4 in.) in length when mature and yellowish in colour, but this colour is hidden by a black deposit of their fecal material making it slug-like in appearance. This creates a dome around them, keeping them moist in dry conditions while protecting them from predators.  When this outer coating is removed, you will find a yellowish beige larva underneath with a brown head and three pairs of small brown legs at the front of the body. 

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. Scout every 5 days, as damage can increase dramatically within days. 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.

In winter cereals, 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. In spring cereals, if an average of three larvae per tiller are found before boot stage, spray is warranted. Malathion is the only product registered for CLB, now that lambda-cyhalothrin products can not be used on field crops. Malathion is very harsh on beneficials and pollinators, so only apply these if thresholds have been reached and time the application for after 8pm, when pollinators are less likely to foraging any flowering weeds in or adjacent the field. Before applying an insecticide, provide beekeepers within 5 km of the site advanced notice of the application, to ensure hives can be located strategically, temporarily protected or relocated where feasible.

More information on cereal leaf beetle can be found on OMAFRA CropIPM and the OMAFRA Crop Protection Hub.