How Does Oak Wilt Kill an Oak?
The Oak Wilt fungus, Ceratocystis fagacearum, enters an oak
either through a root graft or a fresh wound. Once inside the tree,
the fungus grows in the water carrying vessels of the tree and spreads
throughout the roots, trunk, and branches. As a mode of defense,
the tree attempts to stop the spreading fungus by producing gummy
substances, called tyloses. Tyloses clog the water vessels within
the tree, but do not stop the fungus. The lack of water flow causes
leaves to wilt rapidly and fall to the ground. So, in effect, the
Oak Wilt fungus stimulates the tree to kill itself.
How is the Disease Spread?
Oak Wilt is spread in two ways; overland infections and root graft
infections. Most overland infections are initiated by fungal spores
transported on the bodies of sap feeding Nitidulid beetles. The
spore pads only grow beneath the bark of diseased red oaks. Nitidulid
beetles feed on the spore pads, which are exposed when the pads
form pressure pegs cracking the bark open. The contaminated beetles
transport the spores to fresh wounds on healthy red and live oaks.
Root graft infections account for approximately 90% of the spread
of the disease within an infection center. Oaks within 50-100 feet
of one another often will have a common root system due to root
grafting. Rarely do trees of different species graft roots. The
root grafts allow the oak wilt fungus in a diseased oak to travel
within the water carrying vessels through the root grafts into a
healthy oak.
What are The Symptoms of Oak Wilt? Symptoms of oak wilt can be easily
confused with other Oak disorders.
Make sure that the symptoms your tree is expressing are consistent
with the following descriptions before concluding you have Oak wilt.
Each of the families of oaks – Red, White and Live express the disease
differently. However, they have one key symptom in common – leaf
drop. Leaf drop is an important symptom because most other Oak maladies
do not cause leaf drop.
What Do I Need to Know About Pruning Oak Trees? Texas and Southern United States Avoid pruning your oak
trees except in January and February. . During this time of year,
the spore carrying beetles are most active and oak wilt spore production
may be present..
Central United States Avoid pruning your oak trees during
the growing season. During this time of year, the spore carrying
beetles can be active and oak wilt spore production may be present.
Northern United States Avoid pruning your oak trees from
April 15 to October 15. During this time of year, the spore carrying
beetles are active and oak wilt spore production may be present.
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 |
 Overland
infections by beetles account for a small percent of new infections.
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Root
graft infections cause most new oak wilt cases. |
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