of Rhode Island GreenShare Factsheets
maggot may seriously injure cabbage, cauliflower, turnip, radish
and related crucifer crops. Early-planted crucifers or seedbeds
of late ones are more likely to be attacked. The young maggot begins
feeding on the tender rootlets and then rasps out a channel in the
main root of the plant. An early indication of attack to the cabbage
plant is the plant wilting during the heat of the day. The plants
may also take on a bluish cast. The plant either dies in a few days
or persists in a sickly condition for some time. In cases where
the plant dies quickly, there usually are a
large number of maggots that riddle the root, making way for decay
organisms to enter and take over quickly.
Cabbage maggot adults are true flies, slightly smaller than the
common housefly. The flies themselves, which are gray and long-legged,
are seldom seen by the home gardener. The larvae are white and legless,
tapered towards the head, and have a pair of black mouth hooks which
curve downward for rasping. The puparia are reddish or tan capsules
resembling grains of wheat in the soil near the plant.
adult flies emerge from the soil where they overwintered as pupae
about the time the first crucifer plants are set in the garden.
The females either tuck the eggs down between the plant stem and
the soil of transplants or lay eggs directly on the soil in a recently
planted field so that the young plant is attacked at emergence.
Eggs hatch in 4 to 10 days, and in about three weeks the maggots
are fully grown. The pupal stage lasts 12-18 days before the adults
emerge. There may be four generations of cabbage maggots in a season.
The first occurs in late April through May, the second in late June
to mid-July, the third in mid-August and the fourth in the fall.
first generation is the most important to control because plants
are small and very susceptible to damage. Natural predators usually
provide a good degree of control later in the season as well. Radishes
in home gardens can be grown in successive plantings, seeding at
weekly intervals--in this way some will avoid damage. Infested radishes
should be pulled and destroyed (not composted) if cabbage maggots
best control method consists of preventing the flies from laying
eggs. Barriers (row covers) or netting of fine screening can be
used for this purpose. In order to be effective, there must be no
gaps or tears in the material, the material must be placed over
the crop before or immediately upon crop emergence or transplanting,
and no hosts of the pests should have been grown on that site the
previous year. It is also important to bury the edges of the netting
so that flies cannot get under the edges, and to allow the cover
to be a little loose so the plants have room to grow. Shields constructed
of tar paper, weed fabric or old carpeting may also be used. The
shield will serve as an egg-laying barrier to adult flies. The shields
are cut into 15 cm (6 inch) squares or 25.5 cm (10 inch) circles
with a small hole in the center, and a slit is cut to the center.
These are placed around the base of the transplant. Press them against
the soil so that adult flies cannot crawl underneath.
an insecticide is needed, be sure the crop you wish to treat is
listed on the label before treatment. Follow the label instructions
from the Cornell Cooperative Extension, 1999
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
of Rhode Island Cooperative Extension provides equal program