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