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Oaks have held an important place in human culture.
Oaks grow best in acidic soil. Once they have been in an area long enough the
tannic acid in their leaves raises the acidity of the soil (Tatter, 1978).
There are many oak species and they often hybridize. There are two major
classes of oak: the red oaks and the white oaks. The leaves of red oaks have
veins that run beyond the margin in the form of a bristle. Red oaks also
usually have four stamens in each floret and the scales on the acorn cap are
comparatively thin. The acorn itself can also be very different where the inner
shell is lined with fine hairs. White oaks' veins never extend beyond the margin
of the leaf. Usually each floret contains 6 to 8 stamens. The scales that make
up the acorn cup are woodier with a knobby base. The inner surface of the acorn
is smooth. White oaks can be found thoughout the world however, red oak is only
found in North America (Peattie, 1950). |
| Oaks have been traditionally planted as shade
plants for houses across the United States. Urban life can cause many stresses
on the oak tree, which are not well adjusted to human disruption. The soil
found in roadsides often lacks the proper nutrients for shade trees. Oaks grow
best in acidic soil however, turf grasses grow best in basic soils and many of
their fertilizers are alkaline. Competition for water with grass also stresses
oak trees. Insects, including gypsy moths, cause defoliation. Signs that a tree is stressed include early
autumn senescence, late flushing out in the spring, and a lower growth rate.
Being aware of and treating the causes of stress can restore the health of a tree.
Stress makes a plant more susceptible to disease (Tatter, 1978). |
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Oak Wilt:
The affects of disease differ among the red oaks
and the white oaks. For example red oak is affected far more strongly by oak
wilt then white oak. In the red oak the symptoms of oak wilt first appear in
the mid-spring when the leaves at the top of the tree become water soaked. The
water damage causes the leaves to turn yellow or brown. The infection travels
down the tree killing leaves causing the tree to lose all ability to photosynthesize. Dependent on the size of the tree it will be dead within a few
weeks, where larger trees may survive until the end of the summer. White oaks
express similar symptoms, however the disease only affects one branch at a time.
Oak wilt is the result of a fungal infection of Ceraticysitis fagacearym.
The fungus will over-winter in dead trees in the case of red oak or dead
branches in white oak. Insects will spread the fungus to susceptible trees
through the wounding of trees during feeding. Root graphing can also spread the
disease among individuals. The best way to treat this disease is to remove
infected trees from the community. In the case of white oaks dressing insect
wounds can contain the infection. In some cases root graphing is prevented by
digging trenches between trees or with the application of a soil fumigant
(Tatter, 1978). |
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