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Get Out and Scout – Don’t Let Flea Beetles Ruin Your Canola Crop this Spring

By Matthew Struthers, Crops Extension Specialist, Moose Jaw

May 2022

Now that the weather has warmed up in Saskatchewan, flea beetles are starting to emerge. Canola seedlings will also be emerging soon, putting them at great risk of becoming consumed by hungry adult flea beetles. There are two early-season flea beetles to be wary of: Phyllotetra cruciferae, the crucifer flea beetle and Phyllotetra striolata, the striped flea beetle.

Flea Beetle Damaged Canola Cotyledon
Flea beetle damaged canola cotyledon

In canola, most of the damage occurs at the cotyledon up to the four-leaf stage. Heavy infestations can destroy the cotyledons, first leaves, petioles and stems. Heavy damage can occur on hot dry days and results in crop thinning and delayed growth and development. Heavy feeding can destroy entire crops or limit the plant's ability to regrow if growing points are destroyed. Flea beetle damage can delay maturity, exposing the crop to adverse growing conditions later in the season that can cause reductions in both quality and yield. These issues can be largely avoided if canola is protected from flea beetle injury during the first two to three weeks after emergence.

Scout fields and assess plant damage as often as possible throughout the cotyledon to four-leaf stage, and make sure to inspect the stems and undersides of leaves. Continue to scout until the crop has surpassed the four-leaf stage and is no longer vulnerable to feeding damage, which appears as chew holes on the leaf surface and leaf edges. Damage may be most severe along field edges, low-lying areas or shelters where the adult flea beetles overwinter. During cooler temperatures, flea beetles are more likely to walk or hop into adjacent crops; once it is warmer than 14 C they will fly, spreading further into infested fields or onto adjacent fields. It is important to begin controlling flea beetles early before they get out of control.

Using good quality seed with high germination and vigor will help reduce the impact flea beetles have on the crop. Seeding in proper environmental conditions that promote fast germination and rapid seedling growth will limit the amount of time the crop is susceptible to damage. Seeding into standing stubble can provide a cooler, shaded environment that is less favourable to feeding. Increasing the number of plants per square foot by upping the seeding rates will reduce the feeding damage per plant and allow for plants to fill in areas where plants were eaten off completely.

Seed treatment insecticides can be effective at controlling flea beetles and keeping them under economic thresholds. If feeding damage exceeds the economic threshold, then a foliar insecticide application should be considered to limit economic loss. When considering additional insecticide applications, all thresholds, expected plant stands and anticipated damage must be considered as well as cost.

Scout various areas throughout the field to get a good overall average of the feeding damage and determine if flea beetle activity is concentrated in an area of the field. Refer to the 2022 Guide to Crop Protection for available insecticides for flea beetle control in canola.

Flea Beetle Diagram
Estimating when flea beetle damage on canola has reached action threshold.
Photo Credit: Canola Council of Canada

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