How to Spot Signs of Tree Disease
Whether you’re drawn to sturdy oaks or delicate flowering cherries, trees can transform a barren yard into a lush landscape. Unfortunately, they can also suffer from a multitude of ailments caused by pests, fungi and diseases.
Identifying problems early by watching for indicators, such as lesions and changes in leaf color, can be an important step in keeping your trees healthy. In this article, we’ll explore common tree diseases, signs you should look for and what you should do if you think your tree is in trouble.
Tree diseases, fungi and pests can vary, depending on the type of tree you have. However, trees in many regions of the United States can fall victim to the following common maladies:
- Leaf rust: This fungal disease causes red, orange or gold spots on tree leaves. Because leaf rust interferes with photosynthesis, trees with this condition can’t produce enough food to survive.
- Gall: Caused by insects, this fungal or bacterial condition leaves unsightly swellings on tree trunks.
- Anthracnose: Deciduous trees, such as ash, oak or sycamore, can develop anthracnose, which causes dark lesions on leaves, flowers and fruit. Because anthracnose is caused by fungi, trees are more likely to contract it during a cool, wet spring.
- Canker: Canker diseases result from fungus or bacterial pathogens that enter trees through wounds in their bark or sapwood. These intruders can block a tree’s vascular system, preventing the delivery of nutrients to branches and leaves. Although damage is often localized, severe cases can result in tree death.
- Fire blight: Trees or shrubs with fire blight look as if they’ve been scorched, with blossoms and leaves suddenly turning black or brown. Fire blight is caused by bacteria, so it often occurs during warm, moist weather. It can be spread by rain, bees or infected garden tools.
- Diplodia tip blight: Common in conifers, pine needle blights can stunt and eventually kill new growth, resulting in disfigurement or, in severe cases, tree death.
- Powdery mildew: This disease leaves a powdery grayish-white coating on leaves, which eventually results in leaf loss. Plants and trees in shady, humid areas are particularly susceptible.
- Phytophthora root rot: Trees with poor drainage may develop root rot, which results in pale, wilting leaves. The disease may eventually kill the affected tree.
- Japanese beetles: These pests feed on leaves and blossoms. Because they typically don’t eat the veins, affected leaves may have a skeletal appearance.
- Sooty mold: Often affecting evergreen shrubs and deciduous trees, sooty mold leaves a black coating on twigs and leaves. Because it keeps sunlight from reaching the leaves, this fungal disease can prevent photosynthesis.
- Dutch elm disease: This elm tree disease can kill a tree within a year. It’s often characterized by yellowed or wilting leaves, which eventually drop off as branches die.
- Leaf spot diseases: This common family of diseases can be caused by fungi, bacteria or nematodes. Although symptoms vary, depending on the type of tree and the agent causing the problem, these diseases typically cause brown, black, tan or red spots on the affected tree’s leaves.
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For the best outcomes, it’s crucial to identify tree disease early and begin treatment immediately. Fortunately, you can often spot disease by being vigilant and examining trees and shrubs for these common signs and symptoms:
- Changes in leaves: Although changes in leaves may occur as a result of natural seasonal shifts or under- or over-watering, they can also be indicators of disease. Look for browning, wilting, dead spots and changes in coloration.
- Abnormal growths: Unusual growth, such as swollen tissue around the trunk or branches or pustules on leaves, can indicate disease.
- Stunted growth: If new growth is abnormally small or absent altogether, it can be a sign that a tree is ailing.
- Powdery coatings: Powdery white or whitish-gray coatings on tree leaves can indicate fungal growth.
- Discolored or dying needles: Needle discoloration, blistering and loss are often early indicators of pine tree diseases, such as needle blight.
- Brown veins: Browning leaf veins may indicate common oak tree diseases, such as oak wilt.
- Spots on fruit: Certain apple tree diseases, such as black rot, can be identified by the appearance of black, gray or brown spots on fruit.
- Insects: Often, insect infestations can be found by looking for chewed or misshapen leaves, loose bark or silky tents in a tree’s branches. Sometimes, the actual insects are visible. Always check the undersides of leaves during your inspection.
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When you see signs of tree disease, it’s important to act quickly. Begin by removing infected branches and leaves and cutting away abnormal growths. Fungus on trees can often be treated with a commercial fungicide or a spray made from a mixture of baking soda and water.
If you aren’t sure what’s causing your tree’s symptoms, you may need to call a professional. Certified arborists can diagnose, monitor and treat ailing trees. However, severely diseased trees can be a safety hazard and may need to be taken down.
Ultimately, the best way to keep a tree healthy is to prevent disease from occurring. Adequate drainage, proper air circulation and regular disinfectant of pruning tools can help you keep your trees in great shape.
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