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. 

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.

Here are some management steps that can reduce the risk:

Click to enlarge. These paragraphs are from a Canola Digest article on flea beetle management. It is worth reading.

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.

Use safe rates of seed-placed fertilizer. The recommendation is to use only phosphorus in the seed row and no more than 20 lb./ac. of actual phosphate. Higher rates of seed-placed fertilizer add more stress, slow the pace of growth and reduce the stand. 

Till versus no-till. While canola planted into warmer blackened soil may emerge faster, that same warm ground cleared of obstacles also tends to attract more flea beetles. Also, crop residue retains soil moisture, which can contribute to more rapid emergence when moisture is limiting.

Improve results from foliar sprays

Key point: If visible crop damage from flea beetle approaches the action threshold across the field, in-crop foliar insecticide may be required to protect the crop. IMPORTANT: The action threshold of 25 per cent leaf area loss applies to “normal” crop growth situations. In situations with stressed crop, healthy flea beetle populations and warm, dry weather conducive to feeding, spraying before crop reaches the 25 per cent threshold may be advised. (More on thresholds and scouting.)

To improve efficacy for foliar sprays…

Spray when flea beetles are active. Flea beetles are most active when weather is warm, dry and calm. These are good conditions for spraying. In rainy cool weather, flea beetles often take shelter in the soil and don’t feed as much. These are not good spray conditions for flea beetle insecticides, which all rely on contact with the flea beetle target.

Consider the temperature effect on insecticide efficacy. 

  • On hotter spray days, malathion and Sevin XLR may provide better results. The malathion label recommends a minimum temperature of 20°C. The Sevin label includes this statement: “Best control is achieved when product is applied in the heat of the day when insects are actively feeding.”
  • Pyrethroids (Decis, Pounce, Perm-UP and others) have restrictions for application in higher temperatures. For example, FMC staff make the following statement for Pounce: “The recommendation is not to spray when temperatures exceed 25°C. If applications need to be made (or risk crop failure) when temperatures are at or above 25°C, manage the risk and set up it up for success: increase water volumes, make nozzle selection and boom height adjustments to reduce evaporative losses, and spray in the cooler parts of the day.” Research from 1970s (Harris and Kinoshita, 1977) showed that pyrethroids were 2.6 times more potent at 15°C than at 32°C.

Achieve coverage. Flea beetle insecticides do most of their work through contact. Uptake through ingestion of insecticide on canola tissues is considered a “bonus.” Because young canola plants take up only a small percentage of the ground area and because flea beetles are small targets, hitting them requires:

Tom Wolf with Agrimetrix provides this matrix showing coverage based on water rates and nozzle type. Note the improvement in coverage with a medium nozzle at 12 gallons per acre (gpa) water rate compared to a very coarse nozzle at 8 gpa.
  • Adequate water. At least 10 gal/ac. Higher water volumes –15 to 20 gal/ac – can improve results when striped flea beetles are the more common species, and on a cooler windy day when flea beetles have moved down to feed on stems or the underside of leaves.
  • Medium nozzles. Most products call for a medium nozzle – a compromise that improves coverage (compared to a coarse nozzle) and minimizes drift (compared to a finer nozzle). Check labels for specific recommendations because not all labels are the same. For example, the Sevin XLR label reads, “Do not apply with spray droplets smaller than the American Society of Agricultural Engineers fine classification.” Note that tank-mixing flea beetle insecticide with herbicide can reduce insecticide efficacy because low-drift herbicide nozzles, which are a good practice for some herbicides, produce a coarse spray droplet that may not provide efficient coverage or flea beetle contact for top results.

Target sprays (to field edges). Farms may be able to save some money and time with targeted spraying. If scouting indicates heavy flea pressure along one side of a field, spraying only that area can be enough. However, that strategy usually requires spraying quickly after scouting. Within a day, flea beetles may have spread throughout the field. The Voliam Xpress label includes this statement: “To prevent migration of overwintering adults throughout the field, ground spray a 15 metre strip around the field at the first sign of flea beetle feeding.”

Note the permitted applications per year for each product. Insecticides have restrictions on the number of applications per field per year. For example, Decis can be applied three times, Pounce and Sevin XLR can be applied two times, and malathion can be applied only once. For canola growers anticipating more than one insect pest of concern each season, have a product plan to effectively manage pests and stay within label restrictions.

Flea beetle products registered for canola in Canada

Click the product name for a link to its Health Canada label.

Pyrethroids (Group 3A)

Organophosphates (Group 1B)

Carbamates (Group 1A)