Carrot Rust Fly

Host Plants

The larvae of the carrot rust fly feed on carrots and other plants from the carrot family, including parsnip, parsley, and celery.

Regions impacted

Found throughout North America, with particular presence and damage in the Pacific North West and the eastern regions around the Great Lakes.

Description

• The adults are about 1/6th of an inch (6 mm.) long, slender flies with a black abdomen and thorax, yellow legs, and an orange head. Wings are darkish and transparent. The tip of the abdomen of the female is pointed, while that of the male is rounded.
• The larvae are yellow-brown maggots that grow to about 1/6th of an inch (6 mm.) long.
• Eggs are white and about half to one millimeter long.

Life Cycle

• Carrot rust flies overwinter as pupae in grass debris, topsoil, or within carrot roots.
• Adults emerge in May and June and begin mating.
• Females lay up to 40 eggs on the surface of the soil and/or near the base of host plants in clusters of 1 to 3.
• Within 10 days, the eggs hatch into larvae, which burrow into the roots. Larvae feed for several weeks and then pupate.
• Adults emerge approximately 25 days later.
• The carrot rust fly has 1 to 3 generations per year

Damage and Detection

• Larvae of the carrot root fly can seriously damage the roots of carrots and related plants like celery and parsnips.
• Newly hatched larvae enter the root systems of their hosts, feeding until they pupate. The tunnels of the larvae can turn rusty red from the frass or excrement of the larvae and render the host susceptible to disease.
• Symptoms often take some time to manifest, given most of the damage is below ground.
• Symptoms above ground can include wilting and dying leaves, plant dieback, and stunting.
• Beneath the surface, the work of the larvae causes scarring and rotting on older plants and may kill younger hosts. High infestations can make an entire crop inedible.

Prevention and Control

Cultural

• Maintain a clean and weed-free garden to control hiding places in which to overwinter.
• Remove all carrots and other vegetation at the end of the growing season.
• Rather than harvesting or picking a carrot randomly, try to harvest entire sections or rows at a time. This helps prevent larvae from spreading from plant to plant within the soil.
• If possible, delay planting until mid-June to avoid the peak egg-laying period.
• Rotating to non-susceptible hosts can prevent the population from forming. Move the patch every year and try not to return to that location for three or more years, if possible.
• Use floating row covers to prevent flies from landing and laying eggs.

Biological controls

• Milky spores and Bacillus thuringiensis (Bt) are organisms that kill larvae without harm to other life. They are more effective when applied early; they have little impact on mature larvae. Natural enemies of carrot rust flies include the parasitoids Chorebus gracilis and Eutrias tritoma, which target the larvae.
• Plant flowers to attract Ladybugs, which are also natural predators.

Insecticides

Garden pesticides have limited effectiveness. The larvae are ensconced in the roots, and adults are small and difficult to spray. Commercial growers do deploy chemical pesticides during the growing season with various degrees of success. At home, the efficacy of chemical pesticides is low, particularly when weighed against the damage to beneficial bugs and pollinators, and other living organisms.