You can properly identify nearly all ornamental tree diseases simply by inspecting the leaves, fruits and woody parts of the tree. Most diseases that infect ornamental trees are caused by harmful fungi, but some are bacterial in nature. Each tree disease usually produces its own unique symptoms, making disease diagnosis relatively easy. After you’ve identified the ornamental tree disease, you’ll be able to treat the tree accordingly. Depending on the specific disease, treatments can include pruning away and discarding diseased parts of the tree, as well as applying a fungicide, insecticide or other chemical.
Identify powdery mildew disease on your ornamental trees by looking for a white or grayish powder covering the leaves and stems of the trees.
Inspect your ornamental tree for distorted leaves or raised blisters on the leaves to diagnose leaf blister or leaf curl. The infected leaves won’t usually fall off the tree.
Look for swollen growths or sunken areas on the trunks, branches or stems of your ornamental trees to identify canker diseases. In some types of canker diseases, the cankers on the tree will ooze a resin-like substance.
Identify needlecast diseases in ornamental pines, spruces and firs by the severe dropping of needles and browning of needles near the trunk of the tree. Also look for black fungal growths on the infected needles.
Look for substantial defoliation and thinning of the tree’s canopy to detect anthracnose diseases, which are caused by fungi. During late spring to early summer, the ornamental tree may display symptoms including twig dieback, angular leaf spots, cankers on twigs or small branches and veined dead or dying leaves.
Check the leaves of your ornamental cherry tree for round lesions to identify shot hole disease. The lesions will cause holes in the leaves.
Identify verticillium wilt by inspecting your ornamental tree for yellowed leaves, as well as greenish-brown discolored spots on the bark and wood. Whole branches on trees with this soil-borne fungal disease will wilt and die.
Identify leaf scab disease by looking for brownish or olive-brown spots on the leaves and fruits, as well as substantial defoliation. Scab affects only crabapple trees.
Diagnose cedar-apple rust on your apple, crabapple and Eastern red cedar trees by looking for spherical growths or “galls” on the cedar needles and yellow leaf spots on the apple trees. Cedar-apple rust occurs only when Eastern red cedar trees and apple or crabapple trees are planted in close proximity to one another.
Diagnose tar spot on ornamental maple trees by looking for the tell-tale raised spots covering the tops of the leaves. The leaf spots will be covered in a black, tar-like substance.
Inspect your ornamental tree’s leaf tops and branches for a black mold-like growth. This is sooty mold, a fungal disease accompanied by aphid or scale infestations.
Diagnose root rot diseases by checking your ornamental tree for yellowed leaves or needles that have stunted growth and decayed root systems. Phytophthora root rot is a fungal disease occurring in excessively wet soils that can affect ornamental dogwoods, maples, firs, spruces, pines and Leyland cypress.
Identify bull’s eye leaf spot on your ornamental trees by inspecting the leaves for ringed, target-shaped spots. Bull’s eye leaf spot often affects maple, magnolia and sassafras ornamental trees.
- If your flowering dogwood tree has small red lesions around the flowers and on the leaves, the tree likely has spot anthracnose. This type of anthracnose disease doesn't cause defoliation, nor is it fatal.
- Several types of canker diseases exist, some fungal and some bacterial. Endothia canker affects ornamental oak trees, nectria canker infects dogwood, linden and black walnut trees, seiridium canker affects Leyland cypress, black knot infects ornamental plum and black cherry trees, fire blight affects crabapple, pear and serviceberry trees, and Botryosphaeria canker affects many types of ornamental trees.
- Always follow the application instructions on the label exactly when using insecticides, fungicides or any other chemicals to treat ornamental tree diseases.
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