Oak Wilt Disease

Symptoms in Red Oak

The main period of infection is in the spring, when new vessel wood is being formed. Symptoms in red oak occur as early as May. The leaves turn dull green or bronze, appear water-soaked, wilt, and then turn yellow or brown. Damage occurs from the tip and outer edges toward the midrib and base. Wilting leaves typically curl around the midrib and the line between the bronze and green tissues in individual leaves is very distinct (fig. 2). These symptoms quickly appear throughout the crown, often within a few weeks, and leaves at the ends of branches are shed (fig. 3).

Figure 2. – Oak wilt symptonms on red oak leaves.

Figure 3. – Oak wilt symptoms

Heavy defoliation accompanies leaf wilting and discoloration. Leaves fall in all stages of discoloration. Even entirely green leaves may fall from affected branches. Some affected branches hold green leaves longer than others~sometimes until autumn. Therefore, the crowns of trees with oak wilt are seldom as uniformly brown as those of nondiseased trees that have been poisoned, girdled, or killed by lightning. In dry years, the appearance of trees with oak wilt may be confused with that of trees with drought symptoms.

The disease progresses rapidly, and some trees die within 1 or 2 months after the onset of symptoms. Most trees die within a year. Sprouts frequently grow from the bole and larger branches during the year of defoliation or the following year.

 Symptoms in White Oak

The disease symptoms are much more variable in white oaks, although the foliage symptoms are often the same. In a few, particularly bur oaks, symptoms are essentially the same as in the red oaks, and the tree may die within one growing season. Usually, however, white oaks die slowly. Only one or two branches may show symptoms and die in a year. If the fungus persists, a few branches are killed in a season; and over several years, the tree de clines and may eventually die. Some white oaks seem to recover from the disease, but may harbor the pathogen and serve as symptomless reservoirs.

White oaks, unlike the red, frequently have discolored infected annual rings when diseased. Fungus mats seldom appear on white oaks.

Control

Unfortunately, there is no known way to save an oak tree infected by the oak wilt fungus. The only way to maintain healthy trees is through prevention. Early detection and prompt removal of dead or dying trees and breaking root grafts between diseased and healthy trees are essential.

Call 573-789-2556, or email us today for a free consultation on your specific questions about tree diseases.