Oak Wilt is a Fungus
Oak Wilt is a lethal vascular disease that is caused by the fungus Ceratocystis
fagacearum. The fungus lives and grows in the current year’s xylem and all families of
oaks are susceptible. This disease is often misdiagnosed. Oaks attempt to stop the
spread of the fungus by producing gummy substances called tyloses. The combination
of the fungus and tyloses disrupts the flow of water to the canopy and contributes to
the leaf wilting and drop associated with Oak Wilt.
Diagnosing Oak Wilt
Diagnosing Oak Wilt begins with observing foliar symptoms, patterns of tree mortality,
and the presence of fungal mats. Foliar symptoms are a great indicator, but are only
present during certain times of the year. Patterns of tree mortality can be viewed any
time of the year and will give a good indication of disease presence. A good way of
diagnosing Oak Wilt is to look around first. If you see odd patterns of tree loss in an
area, you may find the progression of Oak Wilt. Fungal mats form on Red Oaks in the
spring and are great indicators when found. The fungus produces pressure pads
between the bark and the wood, which cracks the bark open and emits a fruity odor.
Leaf symptoms on Live Oaks are easily noticeable. Leaves will develop a yellowing
and eventual browning of the veins, which is called veinal necrosis. Red Oaks will
often turn pale green and then brown. It is common to find partially dying leaves, of
both Live Oaks and Red Oaks, lying underneath a tree. Unlike Live Oaks symptoms
on Red and White Oaks progress from the outside margins to the inner leaf.
Sapwood streaking beneath the bark is a diagnostic indicator of infection in the red
and White Oak families. This brownish discoloration may not always be apparent,
however, but even if it is not seen, Oak Wilt may still be present.
• Oak wilt is a lethal fungal disease that grows in the water conducting vessels (Xylem) of Red, Live and White oak tree families.
• Oak wilt is found throughout the central US from Minnesota to Texas and as far east as Western North Carolina
• Oak wilt is commonly confused with other oak disorders, but can be diagnosed easily by understanding the symptoms
• Most oak wilt is transmitted through roots grafted together under ground from tree to tree
• Disrupting root grafts and macro-infusing the fungicide Alamo into the tree are the recommended treatments by the US Forest Service, Texas Forest Service, Texas A&M, University of Minnesota and the other major universities.
Oak wilt was threatening one of the largest city parks in the U.S. with 14,469 inventoried trees valued at $22 M dollars. The majority of the trees are oaks. Qualifications for this assignment included having experience in identifying and suppressing the disease.
We worked with the city forester in identifying and isolating the oak wilt pockets.
The photo below shows Nathan drilling 11/32 holes lightly into the Sapwood, spritzing water to keep the vessels open. Successful injections have much to do with good translocation of the material.
This was a $35,000.00 Oak Wilt remediation project in which this largest of city parks in the U.S. was divided into three oak wilt control areas. Infected trees were quarantined, and the trees which were not yet showing signs but were close enough to the infected trees and classified as high to moderated risk were isolated with the core infected group.