Causal Organism: Delia radicum

Crops Affected: Cruciferous crops (cabbage, cauliflower, Brussels sprouts, broccoli, radish, rutabaga, turnip, and other Cole crops); canola, mustard, cruciferous weeds

Life Cycle:

• 2-3 generations per season, depending on the year and the location
• Adults are flies
• Larvae are legless
• Flies emerge in spring from overwintered pupae (timing depends on the weather and soil conditions)
  • Fly emergence in the Prairies occurs around the time when Saskatoon berries and Pin cherries start to bloom
• Peak adult activity is generally from mid to late June to after mid-July
• Eggs are laid in the soil near host plants
  • Survival of eggs and new larvae is highest during cool, moist weather
• Larvae feed on fine root hairs of the plant and eventually burrow into the tap root

Symptoms:

• Larvae feed on host plant roots and burrow into the tap root
  • Root damage is usually most severe during cool, wet weather
  • Severe infestations will destroy or stunt young plants
  • Growth, yield and quality will be reduced on larger plants
• Severity of damage is influenced by weather (temperature and moisture)

Monitoring:

• Use sticky traps or sweeps in spring to watch for adult flies
• Pull sample plants from across the field, ensuring tap root is left intact
  • Look for signs of larval tunneling, with channels evident on the outside of the root
• Yellow-pan water traps can be used to monitor seasonal activity but they are unreliable indicators of overall infestation

Management:

• Application of registered insecticides at appropriate times (e.g. at or just after planting) to protect early and late crops, and all root crucifers (e.g. radish, rutabaga/turnip)
  • Typically a drench application (after transplanting)
  • Subsequent treatments may be required
• Delayed plantings (approximately mid-June) may reduce incidence and severity, as plants and roots will be better developed when eggs are laid and egg survival may be reduced by warmer/drier weather
• Use appropriate crop rotations
• Make control decisions based on the influence of weather on egg and larval survival – hot, dry weather favours reduced egg/larva survival
• Tillage prior to seeding or winter can reduce survival of pupae