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Lygus bugs reach economic thresholds in canola fields

Manitoba Insect & Disease summary for July 27

Lygus bug on flax.


Insects: Lygus bugs around economic threshold levels have been noted in a few canola fields in eastern Manitoba. Banded sunflower moth adults have also been noted; late bud to early bloom stage is when sunflowers should be monitored for seed feeding insects like banded sunflower moth, Lygus bugs, and red sunflower seed weevils. Trace levels of soybean aphid have been found on soybeans near Fannystelle and Lac du Bonnet; so far only trace levels have been noted and so far there are no reports of any populations approaching economic levels.

Plant Pathogens: Pathogens of various field crops continue to be reported.

Disease update

Soybeans: Downy mildew in soybeans was reported from Manitoba Agriculture’s Crop Diagnostic lab.

Sunflower: Sclerotinia was reported in sunflower.

Cereals: Low levels of Fusarium head blight (FHB) is being reported in cereal crops.

Lygus bugs in flax

Some have been noticing Lygus bugs in flax and wondering if they could be an economic issue (see photo at top). Adults move into flax from nearby host plants in July when flax produces buds and flowers.

Although Lygus bugs can reach high densities in flax, flax is quite tolerant of their feeding damage under good growing conditions. A study in Manitoba found that under good growing conditions, populations of up to 100 per 10 sweeps were not economical. Whether this tolerance extends to flax growing under less favourable conditions in uncertain. Flax can compensate for insect injury by producing additional flowers.

“Eggs” on heads of cereal plants

Some have been noticing what usually (although incorrectly) get described as eggs on the heads of cereal plants. These are not eggs, but clusters of pupal cases of parasitic wasps, likely a species of Cotesia (see below). They are often parasitizing caterpillars such as armyworms, and before the caterpillar dies it climbs to the top of the plant. When you see a large armyworm near the top of the plant during the day, that could mean they are infected with either a parasitoid of pathogen. Healthy older armyworms prefer to take cover on the ground during the day. Many Cotesia larvae will emerge at roughly the same time from the armyworm, and quite rapidly after emergence form these silky pupal cases in a cluster, often high on the plant. So if you are seeing a lot of these, this is a sign that parasitic wasps have been actively working in the field.

Pupal cases of parasitoid.
Pupal cases of parasitoid. photo: Manitoba Agriculture

To read the full Manitoba Insect & Disease Update for July 27, complete with current insect monitoring programs and trap counts, click here.

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