There are some ways to tell if your trees have contracted an illness. Here are some tips on what to look out for, and what you can do to help prevent and control tree diseases. Prevention and early diagnosis is the key to maintaining a healthy tree.

Gardeners do their best to keep their plants as healthy as possible. On top of ensuring that every plant receives sufficient light and water, they must also protect the plants from contracting diseases. Tree diseases are particularly devastating and, if left untreated, can spread throughout your yard and infect neighboring plants. Often, this results in having to remove a formerly beautiful, healthy tree from your yard. Here are some common tree diseases to watch out for:

Powdery Mildew

tree disease

This fungal pathogen is a danger to your whole garden, as it affects more than just trees. Typically, you’ll notice a mass of white fungal threads growing along the surface of afflicted plants. This is called mycelium, and it's from here that spores are secreted to produce more fungus. The disease can spread to any leaves, flowers, or shoots growing from the tree and in some cases can result in premature defoliation. Powdery mildew can also grow on roses and bring flower production to a complete stop. It is unsightly and as noted, can infect more than just your trees.


This is another disease caused by fungal invaders and is most commonly found among trees and shrubs in North America. It can impact many different species, though flowering dogwood and sycamore are particularly susceptible. The symptoms of anthracnose vary depending on the type of fungus attacking the tree—and on the type of tree being attacked. Some prevalent symptoms include blight, premature leaf defoliation, and even tree death.

Lethal Yellowing

This is one that palm tree owners need to be wary of, especially those living in Texas or Florida. Typically, this disease favors coconut and date palms. Yellowing is caused by bacteria-like parasites called phytoplasma, which are transmitted to the palm upon coming into contact with an insect carrier. Symptoms include yellowing of foliage, flower death, and premature dropping of fruit. Palms generally die within three to five months after being exposed to the infection.

Oak Wilt

Oak wilt is another fungal infection that results in tree death. Mainly transmitted by root grafts and beetles, the disease causes leaf wilt, rapid discoloration, and premature defoliation among red and white oaks. The veins of affected live oak leaves will turn yellow before falling off completely.

Thousand Canker Disease

This particular disease affects walnut trees in the Western United States, though other breakouts have been recently reported in places like Tennessee. Walnut twig beetles transmit the infection after burrowing into the tree's branches and forming nests, or galleries. In about a month, black cankers form around these galleries and spread to the tree's tissues and branches. Since the cankers only form internally, a tree may be infected for years before displaying any outward symptoms. The foliage on the upper branches will begin to progressively wilt and yellow as the tree declines in health. Most trees that contract Thousand Canker Disease die a few years after they begin to decay.

Apple Scab

This particular fungal disease affects crabapples in the early part of the growing season. Scab-like lesions form on the tree's leaves and cause premature defoliation. Luckily, this disease is mostly aesthetic and is non-lethal to the tree itself.

Cedar Rusts

tree, disease

This is a foliar affliction that commonly attacks rosaceous plants like crabapples and hawthorn. Typically, some kind of cedar tree is required to host the disease-carrying fungus, though junipers provide adequate substitutes. Slimy, spore-producing structures will appear on contaminated juniper branches. You’ll notice rusty-colored or orange spots forming on the leaves in the spring. Cedar rusts can also cause twig cankers and result in dieback, in which parts of the tree begin to die one by one.

Tree Disease Control and Prevention

There are a few things you can do to control and prevent tree disease. Pest-transmitted pathogens can easily be kept away by applying the right pesticides to your plants. Trees suffering from fungal illness should be treated with fungicide at bud break, or at least as soon as you discover the disease. Pruning away small, diseased areas can also help curb the spread of disease. In some cases, unfortunately, it's best to remove the entire problem tree while before the pathogens get a chance to spread. When pruning, remember to bag and destroy any affected foliage and to disinfect your shears or pruners when you are finished.

Anyone that has had a dead or dying tree fall on their property understands the dire consequences of tree disease. When faced with a potential outbreak, a trained arborist is probably your best bet on determining the proper course of action.