Carrot Rust Fly

Identification

  • Larva is light yellow maggot
  • Black fly that has some green markings and an orange head and is about a quarter of an inch long. 
  • Larva can be confused with carrot weevil (see carrot weevil page for more details)

The spring generation of the fly lays its eggs on the ground at the base of the carrot plant in mid-May to early June. The young larvae burrow into the soil and feed on the small roots of the growing carrot. Then the older larvae enter the main root. When the larvae mature they leave the carrot and pupate in the soil. The second generation of adult flies emerges from the pupae from mid-August to mid-September and lays another batch of eggs that produce the maggots that develop in storage carrots.

https://www.mofga.org/resources/pest-control/carrot-rust-fly/

Commonly Affected Crops

  • Carrots
  • Parsnips

Damage

  • Damage can be confused with wireworm damage.
  • The tunnels can be seen on the surface of the carrot and are rusty in color due to the maggot’s excrement – hence the name of the pest. 

https://extension.usu.edu/vegetableguide/root-crops/carrot-rust-fly

Management Techniques

  • We scout for carrot rust fly by putting out sticky cards during the season that they are active.
  • We also scout for damage while cultivating and harvesting carrots and remove the tops from the field when harvesting.

Other Suggestions for Management

  • If carrots remain in the garden, these larvae mature, leave the carrot, pupate in the soil over winter and emerge in spring as flies. Wild and volunteer carrots, parsley, celery, coriander and parsnips are other hosts, and rust fly larvae from these crops mature and pupate in the soil, so crop rotation is unlikely to provide control.
  • If feasible, rid the growing area of all hosts the year before growing carrots, and, in any fields that had hosts, plow deeply in the fall to bury overwintering pupae.
  • Planting later than the end of May will avoid the first generation of egg-laying flies. Harvesting an early planting by mid-June will get carrots out before the larvae enter the taproot or grow large enough to be noticed.
  • Harvest early plantings in blocks and be sure to harvest the crop completely so that the area will not produce second-generation flies.
  • Sprinkling rock phosphate around the base of the plant is said to deter egg laying.
  • Some folks say that beneficial nematodes help reduce populations, especially when crops that confuse the fly, such as onions, leeks and crimson clover, are grown with the carrots. Recent research in Washington State did not support interplanting with crimson clover as a control.
  • By far, covering the planting with floating row cover is the best control – especially if you have had repeated problems with the pest and know that it overwinters regularly in your area.
  • For large scale plantings apparently a netting fence can also be effective as carrot rust flies don’t fly very high off the ground.
  • Carrots that are relatively large in August, when the second generation of egg-laying flies is active, and that are intended for late fall harvest are most important to cover.
  • Early carrots that are large when the first generation is laying eggs, from mid-May to June, may also be important to cover if you plan to harvest those carrots in late summer, since that would give the larvae time to grow.
  • https://www.mofga.org/resources/pest-control/carrot-rust-fly/