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Canola under pressure from cutworms, flea beetles

Manitoba Insect & Disease Update summary for June 1

Insects

Cutworms and flea beetles on canola continue to be the insects of greatest concern. The cool, damp weather from the last few days would have slowed cutworm feeding, and the soil moisture, where not excessive, may help the plants compensate for feeding. Cutworm levels are quite variable, hard to find in some fields, more noticeable in others. So scout for potential cutworm feeding on emerging plants and dig for the larvae if you find an area that is showing signs of cutworm feeding. Precautionary insecticide applications, if cutworm levels are not economical, is not encouraged because of the potential damage to beneficial invertebrates.

Plant Pathogens

Rain has not only provided enough moisture for crops, but also for pathogens causing various crop diseases. Look for early signs and symptoms of diseases in crops. Scout! Scout! Scout!

Current Crop Diseases

Powdery mildew was reported in a winter wheat field in Carman area. Another winter wheat sample submitted to Manitoba Agriculture’s Crop Diagnostic Lab was also found to have powdery mildew.

No reports of stripe rust in Manitoba have been submitted as of today.

The wet conditions resulting from the ongoing rain could potentially favour disease development. Scouting will be important.

Wet Weather and Insects

Cutworms: With all the rain this week, some have been wondering what impact this may have on cutworms. Some species of cutworms are known to spend the day deeper in the soil when conditions are drier. So the cutworms may be closer to the soil surface with all this moisture. This may make them more vulnerable to predators and parasitoids. Wet soil conditions can also promote fungal diseases among cutworms.

Grasshoppers: We were starting to note the emergence of young grasshoppers last week. Excessive rains like these can be detrimental to the young grasshoppers that have emerged. However, grasshoppers that are still as eggs would be resilient to excessive moisture, even if the water pools on the soil.

Aphids: Very low levels of English grain aphid were noted on some of the winter cereals at the University of Manitoba Research farm the last couple of week in May, and some aphids were noted on winter wheat near MacGregor. Heavy rains can be detrimental to aphid populations.

Flea beetles (that feed on canola): There is no research studying the impacts of rainfall on populations of canola feeding flea beetles. Even after heavy rains, our experience has been that on hot, calm days that follow heavy rains the flea beetles are often back on the plants. So once the weather warms up again it is highly advised to scout canola in vulnerable stages for flea beetles.

Insects in Forage Crops

Young larvae of alfalfa weevil have been reported from alfalfa in eastern Manitoba. So alfalfa growers should start monitoring for alfalfa weevil.

To read the full Manitoba Insect & Disease Update for June 1, complete with current insect monitoring programs and trap counts, click here.

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