Shot-hole feeding on seedling canola is NOT a pretty sight in newly emerging stands but growers need to be wary of flea beetles even in the initial 7 days following seeding. The best defense is in-field scouting which continues from germination until the first true leaves unfurl and enlarge in size beyond the cotyledon leaf area. Overwintered adults are highly mobile and attracted to yellow. They even orient towards kairomones released by canola and other closely related Brassicaceae.
Adults are defoliators and small in size, ranging 2-3 mm in length. Even so, the combination of high densities of flea beetles and adverse growing conditions that slow canola seedling growth and extend the vulnerable number of days plants remain seedlings. In some cases, daily in-field monitoring may be necessary to protect canola seedlings from high densities of flea beetles that move into a field en masse.
Several species of flea beetles are present across the Canadian prairies and not all are considered pests. Historically, crucifer (Phyllotreta crucifer), striped (Phyllotreta striolata), and hops (Psylliodes punctulata) flea beetle species have caused damage in canola. Over the past decade, the bluish-black crucifer and especially black-with-yellow-lined striped flea beetles have proven to be consistent economic pests in canola grown across the Canadian prairies.
The 2022 Insect of the Week kicks off by featuring these small yet economically important 2-3 mm long beetles. The adults create shot-hole damage visible on the topsides of the highly vulnerable cotyledons of canola but careful scouting also involves checking for feeding damage on the undersides of cotyledons and tiny stem where they also can feed.
A few key links to aid in-field scouting include:
• PPMN’s Weekly Update from May 2021 (Wk 02)
• Biological and pest management information posted by Saskatchewan Agriculture
• Biological and pest management information posted by Manitoba Agriculture and Resource Development
• The Canola Council of Canada’s Flea beetle pages in the Canola Encyclopedia
• Flea beetle pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (Philip et al. 2018) available as an English-enhanced or French-enhanced version.