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Scouting for and Treating Canola Flea Beetle

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This page was adapted from the articles, "Canola Flea Beetles Feeding Activity Increasing" (June 9, 2022) and "Canola Seed Treatments Waning While Flea Beetles Peaking" (June 16. 2022) which appeared in Crop & Pest Report. 

Flea beetles can cause economic feeding damage in canola and even replanting of fields. Insecticidal seed treatments are waning, and growers have made rescue foliar insecticide applications to stop further feeding damage. It is imperative to scout your canola fields daily for seed treatment failure and economic flea beetle damage. Foliar insecticide application is warranted when 20-25% defoliation has occurred on seedlings through the 6-8 leaf stage.

Several small, green canola seedlings covered in brown spots. A couple of beetle are feeding on two of the seedlings.
Economic flea beetle feeding injury, >25% defoliation, to canola cotyledons grown from untreated seed.

Two species, Phyllotreta striolata, the striped flea beetle, and P. cruciferae, the crucifer flea beetle, account for most of the flea beetle observations in North Dakota canola fields. The striped flea beetle tends to emerge earlier and be less common than the crucifer flea beetle. Both beetles are oval shaped and small, typically between 1/32nd to 1/8th of an inch in length. Both beetles are black with an iridescent blue sheen on the wing covers, however, the striped flea beetle has two yellow longitudinal bands on their wings. Flea beetles have enlarged hind legs and will jump when they are disturbed.

Two crucifer flea beetles and one striped flea beetle small, green canola leaf
Crucifer and striped flea beetles feeding on canola cotyledon

Flea beetles overwinter as adult beetles in the leaf litter of grassy areas and shelterbelts. There is one generation per growing season. Warm and dry weather can promote rapid flea beetle emergence and increased feeding activity. 

Scouting

When scouting, look for the presence of striped and crucifer flea beetles, and examine the cotyledons and emerging leaves closely for pitting and shotholes. Make note of which species is most dominant – current NDSU research has demonstrated that striped flea beetles are not as well controlled by neonicotinoid and diamide seed treatments as compared to crucifer flea beetles. A flea beetle population dominated by striped flea beetles could cause greater and more rapid seedling injury than a population dominated by crucifer flea beetles. A foliar treatment is warranted if 20-25% defoliation has occurred on seedlings through the 6-8 leaf stage. Foliar insecticides for flea beetle control in canola are limited to the pyrethroids:  bifenthrin (Brigade, Sniper, other 2 lb. bifenthrin products), deltamethrin (Delta Gold), lambda-cyhalothrin (Silencer, Warrior II, other 1 and 2 lb. lambda-cy products), zeta- cypermethrin (Mustang Maxx) and two premixes - bifenthrin + sulfoxaflor (Ridgeback) and lambda-cyhalothrin + chlorantraniliprole (Besiege). Keep in mind that new growth after application will not be protected, so scouting after a foliar application is a must.

Treatment

 

Initial results from our insecticide seed treatment trials here in Fargo look promising so far. Canola was seeded on May 23 and is in the cotyledon to 1-leaf stage as of June 6. Flea beetles are feeding, and our Fargo population is about 75% striped flea beetle, and 25% crucifer flea beetle. We’re testing commercial rates of thiamethoxam (Helix) alone and in combination with cyantraniliprole (Lumiderm, Fortenza), and clothianidin (Prosper) alone, in combination with cyantraniliprole and in combination with flupyradifurone (Buteo Start). Initial feeding injury ratings show that all seed treatments are performing well with no significant differences among treatments. However, we did note slightly more feeding injury when thiamethoxam and clothianidin were used alone compared to those same actives in combination with either cyantraniliprole or flupyradifurone. The untreated check plots are well past threshold. Ratings will be done every three days to evaluate continuing insecticide seed treatment performance.

                For more information, please consult NDSU Extension publication Integrated Pest Management of Flea Beetles in Canola, and North Dakota Field Crop Insect Management Guide for a list of insecticides for flea beetle control registered for use in canola.