Insect numbers low, flea beetles requiring some control in canola

Manitoba Insect & Disease Update for May 31

Insect pest concerns are currently low overall.

There have been some insecticide applications for cutworms on corn and soybeans in the Central Region, and on peas and lentils in the Northwest. Some species of cutworms, such as dingy cutworm, have started to turn to pupae in some field. Cutworm staging can be quite variable depending on the dominant species in a field, and the temperatures in the region.

There have also been some insecticide applications for flea beetles in canola, mainly in the Central and Northwest Regions.

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seeding canola

What flea beetle feeding looks like

Flea beetles will make pits in cotyledons, young leaves, and at times on the stems of canola seedlings. Initially fresh pits may be green, but eventually turn a light brown, and holes may appear. It is the extent of this feeding that needs to be monitored (see photo at top of page).

  • Threshold: Some pitting is normal, even if the seed treatments are still at levels that kill flea beetles. The flea beetles need to consume a small amount of tissue to be killed. As a guideline, when about 25% of the surface area of the cotyledons and true leaves have been damaged, and flea beetles are present, an insecticide would likely be economical.
  • Consider the crop stage: Once the third and fourth true leaves are expanded, the canola will likely be able to compensate for any remaining flea beetle feeding.
  • Weather considerations: Flea beetles feed most actively on canola when the weather is sunny, warm, and dry. Cool damp weather reduces the intensity of feeding and aids plant growth.

Agronomists, Farmers, Farm Production Extension Specialists, Extension coordinators, and others scouting crops: Please remember to send in reports of insects or plant diseases over the growing season so we can make these updates as complete as possible, and alert farmers and agronomists where and to what degree insects and pathogens are of concern or being controlled. Information can be sent to: John Gavloski (entomologist) at [email protected] (phone: 204-750-0594) or Holly Derksen (plant pathologist) at [email protected] (phone: 204-750-4248).

Visit the insect pages on the Manitoba Agriculture website at www.gov.mb.ca.

Click here to view the complete Manitoba Insect & Disease Update on the Manitoba Agriculture website.

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