Carrot Rust Fly

Family: psilidae
Species: psila rosae
Common Names: carrot rust fly
Antennae Characters: aristate
Specialties: yellow legs; 6 mm long; yellow head
Hosts: carrots, parsnips, celery, parsley
Cultural Control Methods: delayed spring seeding (mid-may) will reduce severity of attacks. bury culls or otherwise dispose of them.
Pesticides Used: diazinon, cymbush

THE FOLLOWING (UNTIL OTHERWISE NOTED) IS FROM: GERBER, H.S. 1983.
MAJOR INSECT AND ALLIED PESTS OF VEGETABLES IN BRITISH COLUMBIA.
MINISTRY OF AGRICULTURE AND FOOD.

Carrot Rust Fly

Psila rosae (Fabricius)

The major pest of carrots in the southern coastal areas of British Columbia. It is a sporadic pest in
the Southern Interior and Kootenays. Not present in Terrace, Quesnel, nor in the Peace River area.

Vegetables Attacked:

Carrots, celery, parsley, parsnip

Injury:

On carrots or parsnips, larva or maggots feed on the developing roots and root hairs. Larval tunnelling causes a rust-colored etching deforms the root, and permits entry of decay organisms. Plants are stunted The leaves develop a characteristic rusty or bronzed appearance. Young plants may be killed. Late-season attack on established plants causes shallow sub-surface etching on the roots. Maggot feeding may continue in storage and promote rotting.

On celery and parsley, larval feeding destroys the numerous small roots and results in discolored, stunted foliage, making the crop unmarketable.

Insect:

The adult is a two-winged fly about 6 mm long, shiny black with yellow legs. It flies close to the ground near the host plant. The larva or maggot is white, wedge-shaped with a pair of prominent black feeding-hooks at the pointed front end. It is 8 mm long when mature. The pupae are shiny brown, slender, and about 5 mm long.

Life History:

There are two or three generations a year. Pupae overwinter in the soil. Adults emerge from mid-April to mid-May. Each female lays from 30 to 90 eggs in the soil beside the host plants. Larvae or maggots hatch and crawl through the soil to near the root tip. First instar maggots feed on root hairs; later instars feed on larger roots or tap roots, depending on the host plant. Larvae mature in three to four weeks and pupate in the soil. First generation flies emerge from early June to late June; second-generation flies emerge from mid-July to mid-August and remain active until freeze-up.

Monitoring:

Yellow sticky traps are set around the perimeter of the field at 5 to the hectare. The stake, to which the sticky trap is attached, should be adjusted so that the trap is visible above the foliage. When one fly per three traps per day is caught (about 2 flies/trap/week) the application of a control spray is advised. If there is a commercial pest monitoring service functioning in your area, it would be advisable to hire it for this work.

Further information on the preparation and use of the traps and fly identification is available from the Crop Protection Branch, B.C. MINISTRY OF AGRICULTURE AND FOOD.

Control:

Control is preventive; treatments must be applied before damage occurs. Against maggots, insecticides are applied and incorporated into the soil before planting or seeding; against flies, they are applied at regular intervals to the foliage and soil surface. Delayed spring seeding of carrots will reduce the severity of rust fly attack. In the Fraser Valley, carrots seeded after mid-May will escape attack by maggots from flies of the overwintered generation; carrots harvested before mid-July will escape attack by maggots from the second-generation flies.

Cull piles are breeding grounds. Bury culls or take them to a sanitary land fill. Late carrots must be protected with sprays until early November.

Agriculture Canada Insect Identification Sheet No. 57 March 1981

Carrot Rust Fly

Psila rosae(Fabricius)

The carrot rust fly is found across Canada and in the United States. Besides carrots, the insect attacks parsnips, celery, parsley, dill, caraway and fennell.

Injury:

Damage caused in feeding by the yellowish white and legless maggots, which are about 8 mm long when fully grown, results in stunting and drooping of carrot and parsnip plants. In severe attacks, the roots are reduced in size, distorted, scarred and riddled with rust-red burrows of the larvae. Seedlings may be killed or severely stunted if their growing tips are seriously injured.

Life History:

There are two generations of the pest each year in most areas, but a third occurs in southwestern British Columbia and somearial in southwestern Ontario. The pupae, which are about 5 mm long, overwinter at a depth of 5-1 5 cm in the soil of old carrot, parsnip and celery beds. Adults emerge about the end of April in British Columbia and about a month later in Ontario. Their emergence usually coincides with the blooming of lilacs. Soon after they appear, the green, yellow-headed flies deposit eggs in cracks in the soil around the plants or on the stems just below the soil surface. A female may lay 100 eggs in 3 days. On hatching from the eggs 6-12 days later, the larvae enter the fine rootlets before tunneling into the main root and down to the tap root. In British Columbia, the second generation of flies appears in late July and in August, and the third generation in October and early November. In Ontario, the second generation appears from mid-August onward.

Control:

Seed beds may be protected from the flies by covering them with a thin cloth, such as hospital gauze, having 20-30 threads per 2.5 cm. The cloth is tacked to the framework around the bed and supported by wires across the bed at intervals of 2 m. Consult your provincial agricultural representative for control recommendations.

Carrot rust fly ( Psila rosae) rust colored head (same width as thorax) with yellow legs. The insect is fairly host specific, lay eggs at base of plant. Larvae feed on lateral roots and can take nicks out of taproot that can act as ports of entry for secondary infection. Peaks occur in mid-June, mid August, and late October. Troughs in mid-July, mid-September. When carrot plants are very young and exposed, the flies move in during the day and out at night. Stinging nettles and woody or shady areas are indicator species for carrot rust flies and these areas can be staked for early detection.

Monitoring has resulted in a dramatic reduction in pesticide application. Yellow sticky traps are attached to stakes (lathe available at most lumber yards) placed around the perimeter of each field. Stakes are placed approximately 60 paces (100 meters) apart (my pace is 249/153 meters long=5/3=1.63 m => 100m= 60 paces). Too many intermediate traps bring down overall average and result in underestimation of population size. Always stake the corners of the fields but, if this inflates the number of cards, calculate thresholds as if it were stacked with 2 cards per hectare. Increasing the sampling interval can dissolve the population trends to the point where spraying thresholds are missed. The sticky traps are attached to the stakes using "bulldog clips" (available from most office supply store-- but these are expensive) or the much more reasonably-priced alternative: wooden clothes pins (the kind with the metal spring). Place the traps about 8 inches above the ground when plants are in the seedling stage until they attain this height. Then traps should be placed within the crop canopy with half of the trap exposed and moved upwards as the crop grows.

The greater attractiveness that has been observed for the north face of traps may be due to greater activity of flies in the afternoon which would relate to greater brightness of north face. Trap efficacy decreases significantly after a week. Traps should never be kept more than a week.

THE THRESHOLD IS A FLY/TRAP/DAY VALUE OF .25 F/T/D (or greater than .1 F/t/d for more than a week) as recommended by Bob Vernon at Ag Canada (1996).

When flower heads appear these serve as a food resource (nectar) and shelter for adults and the ecological dynamic changes because fly population becomes resident in the fields. Monitoring becomes less predictive because the trap system is based upon the ability to measure traffic into fields that adult flies must leave to seek food.

When the crop is mature it is better to err on the side of recommending sprays because mature crop represents mature investment.

Synthetic pyrethroids (Cymbush) should be used rather than OP's during this time for more effective kills and because of their shorter pre-harvest interval.

Mature carrots can put a root too deep to be marketable. Clipping the tops at maturity decreases the possibility of foliar pathogens developing and keeps the roots from getting too large to be easily harvested/marketed. Clipping should leave about ten inches above-ground to allow for mechanical harvesting. Leaving outside of fields will make the edges, in effect, a trap crop (to which pesticides can be applied when infestations appear localized therein).

For our small fields (less than 5 Ha) it's probably not a very good idea to recommend spot treatments.