By Shiela Miller, Intern Extension Agrologist, Moose Jaw
As seeding begins to wrap up in Saskatchewan and canola seedlings begin to emerge, growers should be on the lookout for a few species of flea beetles. Of the eight flea beetle species that attack canola, there are only two species of this early-season pest in Western Canada that are of concern: Phyllotreta cruciferae, the crucifer flea beetle and Phyllotreta striolata, the striped flea beetle.
Flea beetles feed on the cotyledons, leaves, petioles and stems of crucifer crops (canola, mustard) and weeds (flixweed, stinkweed, shepherd’s-purse, wild mustard). Feeding activity increases under sunny, hot and dry conditions, where heavy infestations can cause severe damage. This can result in crop thinning, delayed crop development and uneven crop maturity. Under cool and damp conditions, flea beetles tend to take cover, which may lead to feeding on the young stems or on the underside of the leaves.
Scouting should be done regularly after plant emergence until the four-leaf stage, when canola is at its most vulnerable. Once the crop has surpassed the four-leaf stage and is established, it can typically outgrow any feeding damage from this point forward. When examining the crop for feeding damage, look for a shot-hole-like appearance in the leaves.
Flea beetles overwinter as adults within leaf litter, under grass along field edges, under debris beneath hedges and in shelterbelts. Flea beetle damage and infestation numbers may be higher along field edges, low spots or areas around hedges and shelterbelts due to their overwintering habits. When monitoring for flea beetles, weather conditions plays a key role in how they disperse. Under cooler conditions, flea beetles tend to walk or hop into adjacent host crops or weeds; however, once temperatures warm up above 14 C and winds calm down, they will fly and spread among the field or invade adjacent fields.
Using good quality canola seed and planting in an environment that promotes rapid germination and seedling growth can help reduce flea beetle impact on canola. Depending on available soil moisture, plant seeds as shallow as possible to allow for quick germination. Directly seeding into standing stubble will create a micro-climate that will help promote rapid seedling growth and due to its shaded, cooler environment, it is less favourable for feeding. Increasing seeding rates will allow for more plants per unit area, reducing the feeding damage per plant and allowing for quicker recovery.
Insecticidal treated seed can also be used to help protect the canola seedling from flea beetle damage as plants emerge. Keep in mind that cool, dry conditions can affect the uptake of the treatment in the plant.
Use economic thresholds to help decide if foliar insecticides are needed to control the pest. If feeding damage has reached levels of 25 per cent leaf defoliation and flea beetles are still actively feeding, then a foliar application needs to be considered for control. Ensure you are scouting 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. Please refer to the 2021 Guide to Crop Protection for available insecticides for flea beetle control in canola.
For more information, please contact your local crops extension specialist.