Common Tree and Shrub Diseases

Apple Scab

One common infection we see with Crabapples is apple scab. This is a serious fungal disease that causes circular brown spots on the leaves and fruits. These spots will turn into scabs and make spores in the middle of the scabs. We see the leaves and fruit most commonly with these scabs which can cause deformities such as twisted leaves and cracked fruit. 

Plants affected: Crab apple trees

Powdery Mildew

Powdery mildew is a fungal infection that looks like white powder on a tree’s leaves and flowers. This can cause stunted growth in that branch, and leaves may fall prematurely. Powdery mildew is highly contagious as the spores can travel by wind up to 100 miles and it can infect almost any landscaping tree, shrub or ornamental plant.

Plants affected: Maples, Dogwoods, Magnolias, Crabapples, Weeping Cherries, and Oak trees.

Twig Blight

This is a fungal infection that targets younger branches by killing the ends. This turns them brown or ash-gray and the infection will create pimple-like fungal structures where the living and dead tissue meet on the branch. 

Plants affected: Arbor vitae and younger landscaping shrubs

Juniper-Apple Rust

This is a fungal disease that requires two different tree families, the Cupressaceae family, which includes red cedar and juniper, and the Rosaceae family, which includes crabapple, apple, and hawthorn trees to complete its life cycle. Though normally harmless for cedars and junipers, when the spores spread to crabapples or hawthorns they can defoliate the tree. The signs of this infection are leaf spots that start yellow and then turn bright orange/red, small raised black dots in the center of leaf spots, and very short finger-like fungal tubes sticking out the underside of the leaf spots. We can also see leaves turn completely yellow and can also result in thick deformed growth of stems. In rare cases, we can find an orange/rust-colored spore-filled blister on the fruit surfaces.

Plants affected: Cedar, Juniper, Crabapples, and Hawthorn

Armillaria Root Rot a.k.a. “Oak Root Fungus”

This fungal infection attacks and kills the vascular shoots in the woody roots and spreads to the main stem. The infection can get so bad it can girdle the base of the trunk causing the whole tree to die. Some trees are actually resistant to this infection such as crabapple, tulip tree, cherry, and maple. 

Plants affected: Oaks


This is a fungus that attacks the internal flower bracts, the leaves, and then the shoots and fruits of the tree. Signs of this infection are tan spots with sometimes reddish-purple borders on the leaves. This is common during the wet spring months and the fungus is known to survive year to year on infected twigs, fruits, and tree tissues. 

Plants affected: Dogwoods, Crabapples, Maples, Tulip poplars, Cherry, and Weeping cherry trees


These are abnormal growths that occur on leaves, twigs, and flowers of plants that are caused by feeding and egg-laying insects. The growth can be simple lumps to complicated structures, plain brown or brightly colored. Damage is common with aphids, wasps, or mite damage. While mostly harmless to older, well-established plants,  galls can cause death in immature plants and can be an underlying sign of an insect problem.

Plants affected: Oaks, Roses, and Willows are common but galls can appear on almost any plant.

Maple Tar

This is a fungal disease that causes dark round spots on the leaves of your maple tree. While it can be alarming to see, the good thing is that this disease won’t kill the tree but rather is just a cosmetic issue.

Plants affected: Maples including Norway, silver, red and less commonly, Japanese

Oak Wilt

This is caused by a fungal infection that grows through the tree’s water-conducting system, causing the tree to wilt and die. Once a tree is infected with oak wilt it will likely die so prevention is the best treatment. The leaves that fall during this infection are noticeably still partially green. It can also create spore-bearing fungal mats under the bark after the tree’s death. It is spread locally from one infected tree to the nearby healthy trees through root grafts.

Plants affected: Red oak family including red, black, and pine oaks

Needle Cast 

This is a fungal disease that mainly attacks spruce trees by causing the needles to turn brown and fall off. Trees can become more susceptible to needle cast if they are stressed by drought or do not have enough circulation in the lower branches.

Plants affected: Spruce trees 

Dutch Elm Disease

This is a fungal infection that causes the yellowing and wilting of leaves and branches. This can affect all species of elm trees. The main stem/tree will also have patterned striations on the bark that also indicate this type of fungal infection.

Plants affected: Elm trees


This is the yellowing of the leaf tissue due to a lack of iron or manganese. Typically signs are green-veined leaves or very pale, white leaves.

Plants affected: Pin oak, Red maple, White oak, River birch, Tulip tree, Sweetgum, Bald cypress, Magnolia, and White pine


This is a fungal infection that attacks tree leaves. Typical signs are colorful leaf spots, twigs, and fruit malformations. The infection can be caused by several different types of fungi, each suited for different species of trees.

Plants affected: Poplar, Willow, Birch, and Plum trees

If you are battling any of these diseases in your landscaping, All Green can help. Give us a call to find out what we can do to keep your landscaping looking its best!

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