of Rhode Island GreenShare Factsheets
One of the
major pests of birch trees in the northeast is the birch leafminer.
The name "leafminer" is derived from the larval habit of feeding,
or mining, the plant tissues between the upper and lower surfaces
of birch leaves. The trees that are most likely
to be attacked are gray, paper and European white birch. The birch
leafminer is not a native insect; it was accidentally introduced
leafminers are related to wasps. The adults are small, black, four-winged
sawflies about 3 mm (1/8 inch) long. The name "sawfly" is derived
from the saw-like egg-laying organ of the female.
adults overwinter in the soil and begin to emerge in early to mid-May.
They congregate on birches and mate; females lay their eggs in newly-developing
leaves. The eggs hatch in seven to ten days and the larvae begin
feeding, making mines which are small and somewhat serpentine in
form. As the larvae grow, feeding increases and the serpentine mines
often run together to form the characteristic blotches and blisters
on the birch. The larvae mature in one to two weeks, drop to the
ground, and enter the soil to pupate. New adults appear in about
15 to 20 days to start the cycle over again. During a normal year,
a life cycle can be completed in five to six weeks. There are three
generations per year. Only the first generation is considered destructive,
because adult females prefer to lay their eggs in soft, young tissue
and there are very few new leaves available late in the season.
that are attacked soon turn brown. Affected trees, seen from a distance,
have a scorched or blighted appearance that is often mistaken for
a disease. Leaves examined at closer range have a blotched or blistered
appearance. Under normal conditions, the tops of trees are often
the most seriously affected portions, although the entire tree can
be affected. A healthy tree can normally lose part or nearly all
of the current crop of leaves without being seriously weakened.
Repeated losses, however, year after year, will weaken the tree
and may result in death.
insect is normally controlled by parasitic wasps in its native Europe.
URI researchers have established one of these European parasites
in Rhode Island; the wasp has spread throughout the entire state
and is providing a degree of control that is increasing annually.
Before spraying insecticides against the birch leafminer, it may
be worth watching your trees for a season or two to see if the pest
comes under natural control.
you do decide to treat, realize that sprays kill the parasites as
well as the pests. Treat only the first generation by spraying in
early May, just after the leaves unfold and adults are just beginning
egg laying. Several insecticides which are registered and effective
against this pest are available at garden centers. Later treatments
are unnecessary in Rhode Island.
Dr. Richard A. Casagrande and the University of Connecticut Integrated
Pest Management Program, 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