Flea beetles: Management tips

Flea beetle characteristics that may help with management

• Flea beetles in Western Canada winter as adults in sheltered areas, preferably with lots of foliage, and emerge from late April to early June. All of the flea beetles that show up in canola crops each spring are those adults that survived the winter. Egg laying does not occur until May and June, and the next generation of adults start flying in August. Those are the ones observed in late summer and fall. They feed for a bit then seek refuge for the winter. Flea beetle life cycle
• In spring, adults will fly to find the first-emerging canola crops. Distance traveled has not been confirmed, but anecdotal accounts suggest flights of a few kilometres. Odours from the first-emerging canola in an area attract flea beetles. Hear more in this podcast.
• Striped flea beetles are a little more cold tolerant, so in spring become active one to two weeks earlier than crucifer flea beetles. Early-seeded crops, therefore, may have more striped flea beetles.
• Flea beetles are most active when weather is warm, dry and calm. With high winds, the beetles may move down and feed on stems and the underside of leaves. In rainy cool weather, they often take shelter in the soil and don’t feed as much. 
• Because dry weather is ideal for flea beetles and bad for rapid crop growth, dry weather makes the flea beetle risk much worse. 

Crop establishment to reduce risk

Key point: Canola crops that establish quickly and have five to eight plants per square foot usually face minimal risk from flea beetle feeding. 

Flea beetle management scenarios that require multiple in-season foliar sprays are often the result of a slow-establishing non-competitive crop. Many factors can cause this, including moisture, temperature, plant populations, seed treatment and overall flea beetle numbers.

Seed shallow into warm, moist soil
A later seeding date may reduce the flea beetle risk if it means warmer soils and faster growth. Like most agronomy decisions, delayed seeding comes with trade offs: it may reduce flea beetle risk, but may not be ideal to avoid summer heat on flowers and limit fall frost risk. If soils are dry, seeding down into moisture may allow for seed germination, but often results in poor emergence and an extended emergence period. With any delays, seed treatment protection may not last through the at-risk period.

Consider advanced seed treatment

Advanced seed treatments will improve flea beetle protection in high-risk areas. These include Buteo Start, Lumiderm, Fortenza and Fortenza Advanced. Two things about seed treatment: 

• Seed treatments don’t work as well or are not actively taken up when the plant is not growing or when moisture is inadequate for the transfer of active ingredient from seed coat to seedling.
• Flea beetles need to take a bite of the canola seedling to take in the seed treatment insecticide. A bite anywhere will give them a dose (however stem feeding should be assessed as more damaging than cotyledon feeding.)

Target five to eight plants per square foot

A canola plant population at the high end of the recommend range of five to eight plants per square foot will mean more plants for a fixed number of flea beetles. That means fewer beetles per plant, a situation more likely to keep leaf area loss below the threshold of 25 per cent.