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Oak trees (Quercus spp.), although among the sturdiest species growing in Ohio, are still susceptible to diseases that can damage or destroy them. Two groups of oak trees grow in Ohio’s USDA Plant Hardiness Zones 5 and 6; red and white. Vascular and fungal diseases can affect all oak varieties.
White Oaks have rounded leaves of whitish-green; acorns mature within a year after flowering. The bark is lightly-hued ecru (it looks white when cut). These trees grow to about 70 feet high and spread just as wide–larger if they are able to expand in an open environment. White oaks are deciduous trees from the Beech family; they require full sunlight and well-draining acidic soil. This group includes:
Red oaks are deciduous trees from the Beech family with pointed, bristling leaves that alternate seven to eleven lobes per stem. Fall color ranges from crimson to gold and yellow-brown foliage in September, October and November. Red oaks grow to about 60 feet tall and spread 70 feet wide in full or partial sunlight and moist, well-draining soils. The red group includes:
Wilts, blights, blisters, galls, and fungal infections are a few of the maladies that can seriously injure or kill white and red oak trees. Let’s talk about some of the more noted problems for Ohio’s oaks.
The rounded lobes of white oak leaves are mostly susceptible to the pathogens of anthracnose—but pointed red oak tree foliage can also be affected. In overly wet weather, Ohio’s oak trees develop tiny raised-brown fungal spore groups on dead twigs, leaf veins and bottoms. Affected leaves will curl, weaken and often drop.
Depending on the growing cycle, trees may sprout new vegetation within the same season and in single occurrences, oaks generally survive any damage. However, if they are infected several times a season ... or if there is any other type of trauma ... the trees will decline. Natural fungicides may protect new vegetation on valued trees, but they are not necessarily effective ways to control onsets of anthracnose. Pruning and removing dead twigs when the tree is dormant is recommended.
Fungal spores form underneath the bark of Ohio oak trees to develop into small, ecru-colored mushrooms at trunk bases. These mushrooms typically grow from 1 ½ to 6 inches wide. The dry caps get a bit slimy after rainfall as stems grow from 2 to 6 inches long. Dark-brown shoelace-like threads (called rhizomorphs) grow on the trunk, roots and under the bark. Ideally, infected trees should be removed but an arborist can recommend specific treatments based on soil and environment.
Mid to late summer in Ohio can get very hot; especially in those dry dog-days of August. When the edges of early-spring oak tree leaves begin to brown, a dark red rusty-like hue develops on the tissues of the foliage. The brown scorching spreads to other branches and leaves.
Because insects (such as leafhoppers and spittlebugs) carry bacteria from tree to tree, Bacterial Leaf Scorch can cause entire trees to die. Professional arborists can inject doses of oxytetracycline into trees; the treatments may reduce the visibility of symptoms but they do not cure the tree indefinitely. Oaks with Bacterial Leaf Scorch must be treated consistently for long-term health.
Galls—the swelling of tissues on trees and plants— often form on stems, crowns, and roots. Galls can damage the roots of mature oaks, making them susceptible to other diseases. Sponge-like galls become hard as they age; the outer tissues will rot and eventually fall off.
Ganoderma Root Rot infects oak trees—as well as some firs and other deciduous species. The fungus enters and spreads through the lower trunk; it weakens the main stem where high winds can then cause structural damage.
Fruiting spores develop into ecru-rust colored layers that settle on the trunk and roots. Also called “butt rot,” this fungal shelf grows wider every year. Oak trees won’t necessarily die from this exposure to Ganoderma, but their weakened wood can fall and cause property damage.
The fungal structures of I. andersonii form yellow brown-yellow spores that attach to the undersides of tree bark. The fungi can enter Ohio oak trees through trunk damage and branches—tree limbs break at these cankers. Red oaks and other trees that have been weakened by droughts and wounds are most susceptible to these types of cankers.
Much like other pathogens, Hypoxylon Cankers on red and white oak trees bring about yellow and wilting leaves. Fungal mats develop underneath, pushing the bark to fall off. These fungal mats, also called stroma, are tan to grayish-silver on the outside. Hypoxylon Cankers affect oaks that are already weakened by wounds, insects, root damage, heat, and drought. When the wind blows, and even when air is somewhat stagnant, this fungus can show up in healthy trees—it thrives in warm temperatures (60-100 degrees Fahrenheit).
With Inonotus Root Rot, oak trees in Ohio can falter before symptoms become obvious. Much like other diseases, infected trees lose their branches and leaves; they begin to yellow as roots are rotting. When the fungus reaches the butt of the tree, it forms into large, irregularly-shaped light-brown shelves. Removing infected trees is recommended.
Fruiting structures of Laetiporus Root Rot begin developing in the spring; large chunks of yellowish-salmon colored “shelves” turn white as they age throughout the summer and fall. Fungal spores form underneath as oak tree bark becomes cracked and dented. Trees affected by Laetiporus Root Rot are quite apt to become damaged by the wind.
Leaf Spot affects oak trees, especially in mid to late summer—they are dark brown splotches that change to rusty brown with a yellow halo. Although Leaf Spot doesn’t cause defoliation or severely damage healthy trees, those with iron chlorosis or other stresses from drought, heat, wounds and root damage can be an issue.
With Oak Leaf Blister, spots up to a half-inch wide become light green as the tree’s vegetation begins to open. When the spots mature, they develop a whitish coating of fungus that slowly turns to brown. The leaves usually do not fall prematurely. In general, the spots do not severely damage Ohio oak trees.
Powdery mildew is found on many Ohio tree and shrubberies. The white fungus grows on leaf surfaces, mainly in the fall. Typically, powdery mildew does not damage trees.
Red tree varieties in Ohio are most apt to be affected by oak wilt. Foliage turns brown along the leaf tips and margins; it wilts and falls even though leaves may still be tinged with green. Oak wilt kills off twigs and branches—trees often die within a year after being infected.
Controlling oak wilt is a challenge; remove the infected trees upon discovery and do not keep the wood because insects can carry the fungus to nearby vegetation. Fungicide may be useful on a sturdy and mildly-infected oak, but the fungi will remain in root systems. In most cases, however, oak-wilt affected trees will not survive.
Sooty mold is just like it sounds; a crusty and dusty black growth on leaves and twigs of oak trees and other types of vegetation. Sooty mold grows mostly on the feces of sap-drawing insects; scales, whiteflies, aphids and the like. The plants themselves are in no danger of serious damage but thick layers of mold can keep photosynthesis from occurring as needed.
When you see reddish, rusty brown splotches on leaves and tree cankers, it’s possible your Ohio oak has a case of Tubakia leaf spot. Severely-infected trees will drop leaves prematurely, and small fungal spore groups are noticeable on lesions that restrict water movement within the leaf veins.
While these and a number of other diseases can affect your Ohio oak tree, additional factors play a part: age, insect infestation, weight, and physical location.
Fully mature and aging trees often have very heavy limbs. If the tree trunk cannot adequately support these thickening limbs (that can be as large as full-grown trees themselves), the oak’s main support structure will weaken over time and when that happens … crash!
Periodic pruning and evaluation (preferably by tree experts) are recommended to monitor the overall health of oaks growing in Ohio landscapes and gardens.
© 2019 Teri Silver
Alexander James Guckenberger from Maryland, United States of America on January 08, 2019:
There are more diseases than I would have otherwise thought about. Thanks for an awesome article. I love oak trees.