Weekly Cereal Pest, Winter Wheat Growth Staging and GDD Update

May 22, 2024

Cereal Leaf Beetle and True Armyworm Update

Cereal leaf beetle (CLB), and true armyworm are common cereal pests in Ontario. To help support growers in their management of these pests and to better understand their prevalence, 28 fields across Ontario are being scouted weekly for cereal leaf beetle (CLB) and true armyworm (TAW). Crop growth stages are also being monitored.

CLB and TAW have been found at some locations but continue to be well below threshold (Table 1 and 2). All trap data can be found at The Great Lakes Pest Monitoring Network.

The best time to scout for TAW is shortly after dusk when larvae are actively feeding.  In cereals and mixed forages, examine 10 areas of the field, assessing the number of larvae per 30 cm x 30 cm (1 ft2). Pay particular attention to the border area directly adjacent to other grassy host crops. During the day, if it is cloudy and overcast, you might be lucky enough to see larvae on the head of the plant but on sunny days, they will be down on the ground among the crop debris or under soil clods. Brown frass may also be present on the plants and on the soil surface. Birds diving into your field is a good indication that there are good eats there so take a look.

When you do find larvae, look for any white eggs that may be attached to the backs of the armyworm larvae. This is a sign that the larvae have been parasitized by one of its parasites which have done the job for you. Avoid treating with insecticides when large numbers of parasitized larvae are present as they have already been controlled by parasitoids or when larvae are close to 2.5 cm in length, as insecticides will no longer be effective, and the larvae will soon stop feeding.

Chemical control for true armyworm is warranted if there are 4 to 5 un-parasitized larvae per square foot (30 cm x 30 cm). If a significant amount of wheat head clipping is occurring, spray may be warranted if larvae are still actively feeding, are smaller than 2.5 cm and pre-harvest intervals have not been reached.

For CLB, controls are needed if an average of three larvae per tiller are found before boot stage, or one CLB adult or larvae per stem after boot but prior to heading. Chemical control products for winter wheat against TAW and CLB can be found on the Crop Protection Hub. Currently, TAW levels are low across Ontario, and no insecticide treatments are recommended. CLB has been seen in select counties, with some higher prevalence in more southern regions compared to eastern and northern Ontario

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