Pest Alert: Suspect
swede midge found in Massachusetts (September 20,
The swede midge (Contarinia nasturtii) is
an introduced pest of brassicas that has been found
in Erie, Genesee, Orleans, and Niagara counties in
western New York and in 15 counties in Ontario and
20 counties in Quebec, Canada. Massachusetts Department
of Agricultural Resources and UMass have been working
collaboratively to survey for this pest in Massachusetts
as part of the USDA, APHIS Cooperative Agricultural
Pest Survey (CAPS). Two suspect swede midge specimens
were captured in Hampshire County this summer. One
specimen was caught in a garden in Northampton with
mixed brassica species. The other was from a vegetable
farm in Hadley and was found in cabbage. The suspect
swede midge specimens were identified visually and
with PCR by Dr. Tony Shelton’s lab at Cornell
University. Massachusetts Department of Agricultural
Resources is continuing to trap in Hampshire County
to find another specimen to have its identification
verified by a USDA insect identifier. Several other
states are also surveying for swede midge this year
under the CAPS program. Once the full survey results
are in, we should have a better idea of distribution
of swede midge in the Northeast and what regulatory
actions are most prudent to slow its spread.
How did it get here?
The swede midge is a major pest in Europe where it
is endemic. No one knows how it reached North America
or exactly how long it has been present in Canada.
The presence of the swede midge in North America was
not confirmed until 2000. The symptoms growers in
Canada observed in their fields since 1996 were mistakenly
attributed to nutrient deficiency. Since the swede
midge is a poor flier, this insect is unable to move
long distances on its own. The larvae pupate in the
soil; therefore, soil movement is one way in which
swede midge may move long distances. Transplants are
also considered a vector for transport of swede midge
eggs, larvae, or pupae. Canada has put a directive
in place to regulate the importation and domestic
movement of transplants of host species and soil that
may contain life stages of swede midge to prevent
the further movement of swede midge. Produce is not
seen as a likely vector for movement of the midge.
What does a swede midge look like and what
kind of damage does it cause?
An adult swede midge is a very small, brown fly only
a few millimeters long. Since adults live only a few
days, we use a pheromone trap that remains in the
field for several weeks to catch their them during
their flight period. Males are attracted to the pheromone
lure in the trap and are caught on a sticky card inside
the trap. We look for adults because they can be identified
to species. Larval specimens can only be identified
to genus. Larvae cause damage by feeding on plant
tissue. When scouting for swede midge in the field,
you will see the damage before you see this minute
insect. Larvae are initially small (less than 1mm)
and transparent. At maturity larvae are 3-4mm long
and lemony yellow in color. If you suspect swede midge
larvae in host plant tissue, you can place the tissue
in a plastic bag in the sun or put the tissue in 70%
alcohol to force the larvae out of the tissue.
Damage is more likely to be found around the edges
of fields in more sheltered areas (near hedgerows
or buildings) because the swede midge is a poor flier
and prefers areas of low wind movement. Signs of damage
include: brown, corky scarring; swollen and twisted
leaf stalks, galls at the growth point of the plant,
no head formation, and multi-headed or multi-stemmed
plants. Swede midge damage looks like damage caused
by cultivation, genetic variability of seed, heat
stress, frost damage, or feeding by other insects
(e.g. flea beetle or tarnished plant bug) that can
damage the growing point of the plant. One needs to
find larvae within the plant to confirm swede midge
is the cause of the damage.
What can you do?
Swede midge is difficult to control, and cultural
practices are a big part of the management strategy.
So far, good crop rotation is one of the reasons damage
seen in the United States is not as bad as in Canada.
Suggested practices to minimize the spread of the
swede midge include:
1) Start with clean transplants: Transplants are considered
a likely vector for swede midge movement.
2) Crop rotation out of crucifers for 2-3 years: Pupae
can remain in the soil for 2 years if they don’t
have favorable conditions for emergence.
3) Field sanitation: Controlling cruciferous weeds
eliminates an alternative host for swede midge.
4) Deep plowing and chopped of infested residue: Pupae
are usually found in the top 5cm of the soil; so,
deep plowing will reduce the viable number of pupae.
5) Early planting: Swede midge has between 3-5 generations
per season. Early planting will allow you to harvest
before populations reach their peak.
6) Plant in open fields: Early damage occurs along
tree lines, buildings, and hedgerows.
7) Cultivar selection: Some varieties of broccoli
such as Paragon, Eureka, and Packman are more susceptible
to damage than Everest, Triathalon, and Regal. While
the swede midge will attack any brassica crop, the
highest levels of damage have been seen on broccoli,
Chinese broccoli (gai lan), Brussels sprouts, cauliflower,
Chinese cabbage, and other Asian greens.
8) Preventative insecticide applications: Canadian
growers use acetamiprid on greenhouse transplants
and lamda-cyhalothrin and acetamiprid in the field.
Researchers are continuing to figure out the best
pesticides and application times/techniques for use
against swede midge.
If you suspect swede midge damage in your fields, please email Jennifer Forman Orth or call (617) 626-1735.
Early detection of this pest will allow growers to
implement management strategies to keep population
levels low and take measures to prevent further spread
of swede midge. As any new information about the swede
midge is discovered, it will be posted on our website:
2005 Interim Best Management Practices to Control
the Swede Midge (Contarinia nasturtii Kieffer)
The Swede midge - A pest of crucifer crops
Swede midge fact sheet from Cornell University http://www.nysipm.cornell.edu/factsheets/vegetables/cruc/sm.pdf
Canadian Food Inspection Agency: Interim Phytosanitary
Requirements to Prevent the Entry and Spread of Swede
Midge (Contarinia nasturtii)
The pest alert is from the Massachusetts Introduced
Pests Outreach Project, a collaborative project between
the Massachusetts Department of Agricultural Resources
and the UMass Extension Agriculture and Landscape
Program aimed at preventing the establishment of new
pathogens and pests in Massachusetts. Visit the project
for more information on Swede
midge and other emerging pests or to subscribe
and unsubscribe for pest alerts.