Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES
Birch Leafminer
The birch leafminer
is a small sawfly native of Europe that was first detected in Connecticut in 1923.
It has since spread throughout northeastern North America.
The larvae of the sawfly make
blotch mines in the leaves of most birches. Severe damage may occur to paper birch, gray
birch, and European white birch. Black birch, yellow birch, river birch and
monarch birch are less susceptible. The adult sawfly is a small, 1/4 inch long,
black, fly-like wasp. The larva is very flat, lives within birch leaves and is
white with three black spots on the lower surface.
|
Type of Damage Damage to birch trees is
done by the larval stage as it feeds between the upper and lower layers of
the leaves. This feeding produces large blotch mines in the leaves. Often,
several larvae will completely mine a single leaf. Multiple generations and
high populations can cause damage to almost every leaf by mid-summer. The
mines turn brown and will cause the tree to look dead with wilted brown
leaves. This forces the tree to refoliate and
reduces its ability to produce food for growth. This damage may also make the trees more susceptible
to bronze birch borer attack. Though the adult birch leafminers
are related to wasps, they do not have a sting. |
Figure 1. Birch leaf damage. Early mines on left and
late mines on right.
|
|
|
Life Cycle and Habits Mature larvae over winter
in the soil under host trees. When the
soil warms in the spring these prepupae pupate,
usually in April, to transform into the adult stage. Within a few weeks the adult sawflies dig
out from their earthen cells and fly to the newly expanding foliage of
birches. The small black adults prefer
to mate and oviposit on the upper leaves,
especially in sunny areas. Mated
females use their needle-like ovipositor to punch a hole in the leaf and lay
eggs. Often the female withdraws the
ovipositor without laying an egg. The
damaged spot may turn brown as the leaf expands and hardens. The eggs are
often visible in the tissues between the major leaf veins. They may appear as
small raised spots on the leaf surface. Within 7 to 10 days the eggs hatch
into tiny flattened larvae with wide front segments. These larvae produce a
blotch mine that may join with others. The old mines may contain considerable
amounts of dark fecal pellets. The larvae mature in 14 to 20 days and are
about 1/4 inch long. By this time the larva have the diagnostic small black
square marks on their lower surface. Mature larvae cut a hole in the leaf
epidermis and drop to the ground. Here they dig one to two inches into the
soil to form a pupation chamber. Birch leafminers
usually produce two to three generations a summer. |
Figure 2. Adult Birch Leafminer
(X5)
|
Figure 3. Birch Leafminer
Larva. Underside View (X5)
|
Control Strategies
Birch leafminers
prefer sunny areas but will attack susceptible trees almost anywhere. Birches
tolerate leafminers best when they are planted in
shady, cool, moist areas. Since birch leafminer
attacks may weaken the trees, making them more susceptible to borer attack,
good fertility and horticultural care are needed.
Option 1: Cultural Control - Pupation Barrier Since the larvae must find soil for pupation, place a
black plastic or tightly woven fiber mulch under the tree drip line. Lightly mulch with organic material so that drying can occur rapidly.
Option 2: Cultural Control - Resistant Birches Unfortunately, the birches with the finest white bark
seem to be more susceptible to the birch leafminer. The river birch and Dahurian
birch have bark with curly flakes and seem to be resistant to bronze birch
borers as well as the leafminers. Other birches
resistant to leafminer attack are Schmidt birch,
Monarch birch, black birch and yellow birch.
Option 3: Chemical Control - Insecticides for Adult
Control Several
insecticides have activity that kills adults. Although the first generation
adults are active when the new leaves are about half expanded, emergence may
take place over several days. In Ohio, birch trees are usually attacked by the
first generation of leafminers during the first two
weeks of May. Contact insecticides may need to be re-applied every 5 to 10 days
depending on their residual activity.
Option 4: Chemical Control- Systemic Insecticides for
Larval Control Systemic insecticides,
especially easily translocated materials, can be
applied to the foliage, by soil injection or injected into the tree. Stem or
trunk injection is not recommended on a regular basis because of the tissue
damage caused by the hole drilling. Attempt to control
the first generation of larvae when the mines or eggs are first apparent.
Information obtained through the Ohio State Extension Factsheet HYG-2035_91
Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES