Flea Beetles Setting Their Sights on Canola

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.

Crucifer Beetle on Canola Leaf — photo credit: Whitney Cranshaw, Colorado State University, Bugwood.org

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.

Striped Flea Beetle–Photo: Mike Dolinski, MikeDolinski@hotmail.com

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.

Insect of the Week – Doppelgangers: Bertha armyworm and clover cutworm

The case of the bertha armyworm and the clover cutworm (and other cutworm species)

Clover cutworm larva
cc-by 3.0 Lo Troisfontaine
Bertha armyworm – caterpillar 
Mike Dolinski, MikeDolinski@hotmail.com

Are those bertha armyworms (Mamestra configurata) eating your canola, mustard or alfalfa (also found on lamb’s-quarters, peas, flax, potato)? Or is it maybe a clover cutworm (Discestra trifolii)? [Note: not all cutworm species spend their larval stage underground.] The larvae of the two species are doppelgangers as they are similar in appearance, have a large overlap in host crops, and have similar timing (June-September). Telling them apart can be a challenge but here are few tips to focus on to help distinguish:

Colour:

  • there are generally fewer velvety black clover cutworm caterpillars, with most of the clover cutworm larvae being green or pale brown

Lateral stripe:

  • On the clover cutworm it is yellowish-pink
  • On the bertha armyworm it is yellowish-orange
Climbing cutworm larva – from Cutworm Field Guide
Climbing cutworm adults – from Cutworm Field Guide

In terms of scouting, economic thresholds and control options, treat both species as you would bertha armyworms.

Bertha armyworm – adult
Alberta Agriculture and Rural Development
Clover cutworm adult
cc-by-nc-sa 2.0 Ilona Loser

To learn more about bertha armyworms and clover cutworms, go to the Insect of the Week page or download copies of the Field Crop and Forage Pests andtheir Natural Enemies in Western Canada and Cutworm Pests of Crops onthe Canadian Prairies identification field guides.