Species

Carrot Rust Fly (Psila rosae)

Host/site

Found throughout most of North America, the carrot rust fly attack carrots, parsnips, celeriac and other umbelliferous crops. (better to say crops in the Apiaceae family) Adult females are attracted to the odor of the host plant, and lay their eggs at the crown of the plant. The carrot rust fly maggot damages plants by eating the small fibrous roots and by tunneling in larger roots. Damage and susceptibility to disease increases the longer an infected plant remains in the ground.

Also important to note is that alternate hosts can be found in the Apiaceae family that includes weeds in the area and herbs planted specifically for use in the garden. Queen Anne's Lace for instance is a common weed in the northwest. Any herb like Lovage, Fennel, Parsley and others.

Identification

Appearance

• The adult fly is 1/5 inch (5 mm) long and has a dark, shiny body with straw-yellow legs and head and large red eyes.
• Larvae are yellowish or white maggots about 1/3 inch (8mm) long when mature. The pupal stage is enclosed within a brown puparium 1/5 inch in length.

Indicators

• Affected plants, with large infestations, may become yellow, stunted, and die. However, more often the plant tops continue to look healthy. Maggots often continue to feed in stored carrots.
• A rust-colored material develops in the tunnels. Larval feeding causes scars and distortions of the root leading to a reduced yield. Feeding damage also allows entry of plant pathogens that cause decay.
• Seedling plants can be killed.

Life cycle

• Adult females lay eggs in May and early June on the soil surface around the plants. The eggs hatch in a few days and the maggots, the only plant-injurious stage, feed on and in the roots. After about a month the maggots will become pupae. The puparia stay in the soil near the roots until August when the adult flies emerge. The new flies lay more eggs, which again mature to maggots. This second generation causes plant damage into the fall. The flies that develop in the fall will spend the winter as puparia in the soil or as maggots in the roots. Maggots from the August-September generation cause the greatest damage. There can be a third generation in late fall; November. Over-wintering carrots are particularly susceptible to this generation.

Natural Enemies

Birds can be great predators for any soil dwelling maggot. Chickens can be used to go through fallow ground where pupae are suspected.

Monitoring

The activity of adult flies can be monitored with yellow sticky traps. Three traps are normally placed near the previous carrot or parsnip crop and near. Researchers in the UK have shown that trap counts are increased when traps are set at a 45º angle (Andrews). Traps can be found at local nurseries here and probably many other places in the US.

Peaceful Valley Farm Supply has these traps available for purchase

Action Thresholds

Thresholds vary depending on tolerance for damage. It is difficult to predict damage levels from the number of adults caught in traps, but a widely used monitoring system recommended that protection should start when 2-3 flies are caught per bed in one week, and should continue until counts decline (Andrews).

Cultural and Physical Controls

*Place carrots and other infested plants that are badly damaged in the garbage can quickly. This will eliminate part of the source of next year's rust fly population. Do not compost them.

• Early fall harvesting and storage of carrots in pits and root cellars rather than in the ground help minimize fall infestations caused by late second and early third generation maggots.
• Plant carrots to avoid the egg-laying periods of the fly (example mid- to late June). In cold areas, plant in early summer. In more mild areas, plant in late winter or late summer. Success of this practice depends on neighboring populations, alternate hosts, etc.
• Covering seedbeds with row covers such as those used for cabbage root maggots and spinach leafminer, or individual plants with protective cones can also be used. Be sure to seal them well at the soil line and do not use them on soil areas that were infested with rust fly the previous year.
• Before using carrots, peel off damaged areas. Do not store carrots in ground through winter.

Biological Controls

Birds and chickens serve as excellent biological controls in fallow ground where pupae are suspected.

Chemical Controls

Not recommended.

References

Andrews, Nick. Carrot Rust Fly Biology & Management. Fact Sheet. Oregon State University, Summer 2008. Web. 31 May 2010. <http://smallfarms.oregonstate.edu/sfn/su08carrotfly>.

Antonelli, Arthur L. Carrot Rust Fly. Fact Sheet. Washington State University, May 1997. Web. 31 May 2010. <http://cru.cahe.wsu.edu/CEPublications/eb0921/eb0921.html>.
This is the best fact sheet with the calendar. You might see if you can use the diagram in the fact sheet yourself with credit to WSU. This really helps to understand the timing issues and when to plant.

How to Manage Pests in Gardens and Landscapes. Fact Sheet. University of California Davis, Aug. 2009. Web. 31 May 2010. <http://www.ipm.ucdavis.edu/PMG/GARDEN/VEGES/PESTS/carrotrustfly.html>.

Pacific Northwest Insect Management Handbook. Fact Sheet. Washington State University, Nov. 1999. Web. 29 May 2010. <http://weeds.ippc.orst.edu/pnw/insects?34RUST01.dat>.