Flea Beetle in Spring Canola: Monitor, Identify Fields at Risk & Consider the Weather

Every spring, canola producers monitor new seedings hoping they will not see flea beetle. They are a familiar but unwelcome sight.  A few resources have been brought together here to help with scouting and decision making on control measures.


Once you notice flea beetle in the field, monitor it daily or as often as possible because they advance quickly. Expect to see some feeding damage, as flea beetles must take a bite to die from seed treatment. It is important that you do not spray too soon. Early application won’t protect a field from re-infestation.  Flea beetles are strong fliers and can quickly re-infest a field.

Control is generally warranted when 25% of the leaf surface area is damaged.  The economic threshold is 50% defoliation but intense feeding can quickly take 25% damage to 50%, so 25% is used as the action level.

Credit: Canola Council of Canada

Fields at the Greatest Risk

Fields with thin stands of less than 5 plants/ft2 or where flea beetle are feeding on stems or new growth should be prioritized in terms of scouting and taking action if needed. Stem feeding is less common but will cause greater damage than feeding on cotyledons. A stem chewed right through is 100% feeding damage. Likewise, feeding on the growing point can have a greater impact on crop development. Healthy stands that are growing quickly may not need to be sprayed, and canola can typically outgrow flea beetle damage once it reaches the 4-leaf growth stage.

If the crop is less thrifty because of other stresses, such as nutrient deficiency, wet soils, or frost damage it may have a reduced ability to outgrow or get ahead of flea beetle damage. Likewise, if a field sustains significant flea beetle damage and is slow to grow, it may be at greater risk of swede midge damage. Swede midge typically emerge at the end of May or beginning of June.

Weather Impacts 

Crucifer flea beetles, the most common, all-black species, will reach peak emergence when soil temperatures reach 14-15°C. Striped flea beetles tend to emerge earlier. Once flea beetles have emerged from winter dormancy, they will keep feeding — even at cooler temperatures. Flea beetles tend to fly around on calm days with temperatures above 15°C, and on cooler days they will walk and hop from plant to plant.

If conditions are cool AND wet, hold off on spraying. Flea beetle will take cover and wait for rain to stop.  Product labels also say not to spray if rain is likely within one hour.

Sunny, warm, dry weather increases feeding activity. Cool, damp weather slows flea beetle activity and may drive them down to the stems where they may feed, or the undersides of the leaves, but they tend to survive fairly well in spite of the reduced activity level. If the weather warms up, growers should continue to scout for damaging levels of flea beetles.

Insecticide Application

Registered products can be reviewed on the OMAFRA Crop Protection Hub. The most commonly used product at this time (2024) is Decis. On cool, cloudy or windy days, beetles stay closer to the ground feeding on underside of leaves or stem. It is critical to achieve good product coverage by using appropriate size nozzle providing medium droplet size and good water volume e.g. 65 L/ac (15 gal/ac).

Protect Honey Bees.  Avoid applying insecticides if bees are actively feeding. Be conscious that flowering weeds in fence rows or in the field will be attractive to bees. Before applying a pesticide, advise local beekeepers so they can move colonies out of the danger area.

Winter Canola

There may be flea beetle activity in winter canola, but there are no thresholds in place for flea beetle feeding on flowering canola or canola at pod fill. At this growth stage canola should be able to sustain significant feeding. If there is significant feeding on flower buds or pods, control options should be discussed. Contact Meghan Moran at 519-546-1725 meghan.moran@ontario.ca. Spraying insecticide during flowering is a significant risk to beneficial insects and pollinators.

Flea beetle move to their overwintering sites in August and are not expected to cause significant damage after seeding of winter canola in Ontario.

This article was created using resources made available by Canola Council of Canada, and with support from Tracey Baute, OMAFRA Field Crop Entomologist.