Objectives for better beetle management
By Keith Gabert
Flea beetles are the pest of greatest economic risk to canola production, according to our 2022 Canola Council of Canada survey of canola growers. With more striped species, which emerge earlier in the spring and seem more tolerant of common seed treatments, and with spring weather conditions that challenge rapid crop emergence, flea beetle damage seems worse than ever.
PHOTO: Two species of flea beetle – striped and crucifer – on the same canola plant. Striped species emerge earlier in the spring and seem more tolerant of common seed treatments. Source: Canola Council of Canada
Canola growers have two major objectives to reduce the risk.
Objective A: Rapid canola emergence
The ideal flea beetle buster is a canola crop that establishes quickly with five to eight plants per square foot. More plants mean more food for the flea beetles, which limits the damage per plant. 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.
Management steps to reduce the risk include:
Seed shallow into warm, moist soil. Consider seeding cereals first as they can tolerate cooler spring soils. Seed canola after soils have warmed up and ideally just before or after a spring rain. • Use an advanced seed treatment to improve flea beetle protection in high-risk areas. These include Buteo Start, Lumiderm, Fortenza and Fortenza Advanced.
Use safe rates of seed-placed fertilizer. The recommendation is to use only phosphorus in the seed row at rates of 20 lb./ac. of actual phosphate. Higher rates of seed-placed fertilizer can add more stress, slow the pace of growth and reduce the stand.
Objective B: Effective foliar sprays
Fields under moisture stress may not meet objective “A”. Flea beetles love dry conditions, crops don’t. In that case, growers should set up for effective foliar insecticide. What makes a spray effective?
First, apply it at the right time. Action thresholds for canola are when damage exceeds 25 per cent cotyledon or leaf area loss. However, in warm weather with actively feeding flea beetles and slow-growing crop, this threshold can be passed quickly. Growers will want to anticipate the speed at which damage is developing and proactively begin spraying before 25 per cent defoliation. In some cases, early spraying around headlands may be enough when damage is localized from flea beetles entering the field edge.
“Right time” is also when flea beetles are most active. Warm, dry and calm are good conditions for spraying. In rainy cool weather, flea beetles often take shelter in the soil and don’t feed as much. In these conditions, insecticides, which all rely on contact with the flea beetle target, will have lower efficacy.
Second, consider the temperature effect on insecticide efficacy. On spray days with highs over 25°C, malathion and Sevin XLR may provide better results. On days with highs below 20°C, pyrethroids (Decis, Pounce, Perm-UP and others) will show better results. Pyrethroids have restrictions when temperatures exceed 25°C.
Third, achieve coverage. Flea beetle insecticides do most of their work through contact. Because young canola plants take up only a small percentage of the ground area and because flea beetles are small targets, effective contact requires adequate water (at least 10 gal/ac.) and medium nozzles. Check labels for specific nozzle recommendations. Low-drift nozzles, which are a good practice for some herbicides, produce a coarse spray droplet that may not provide efficient flea beetle contact. Without coverage, results may not be as good as hoped.
This is just a quick overview of the top points. Continue regular scouting for flea beetle damage until your crop is well established. For more on flea beetle management tips and how to make the spray decision, please see our agronomy-based articles in the Insects section at canolawatch.org/fundamentals.
–Keith Gabert is an agronomy specialist and insect management lead for the Canola Council of Canada. Email gabertk@canolacouncil.org.