About Tree Diseases

identify, treat, and prevent common tree diseases

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Anthracnose, Spot  

Anthracnose, Spot  

Anthracnose is a very common disease that attacks a very wide range of plants and trees. There are two ways Anthracnose disease can attack trees: 1) Spot Anthracnose that impacts tree leaves and blossoms, and; 2) the more harmful canker versions that disrupt a tree’s vascular system.

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Apple Scab

Apple Scab

Apple Scab is one of the most common diseases that attack apple trees. Apple Scab is caused by a fungus (Venturia inaequalis) which is most prevalent and aggressive in geographical areas where spring weather is mild (about 60 to 70 degrees F) and conditions are wet.

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Armillaria Root Rot

Armillaria Root Rot (often called oak root fungus, mushroom root rot or shoestring fungus rot) is caused by a fungus found in the soil which attacks and rots the roots of many plants and trees.

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Bacterial Blight

Bacterial Blight causes brown leaf spots (often surrounded by yellow areas) and rapid browning of young shoots. Newer growth is normally more severely infected. Bacterial Blight can attack a wide range of trees and is most aggressive during mild, moist growing conditions.

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Black Knot

Black knot is visible as soft greenish knots or elongated swellings which form on the twigs and branches. The knots develop into black, corky, cylindrical galls that range from about 1/2 to 1 1/2 inches in diameter and may be more than 12 inches long. Branches beyond the galls are often stunted or dead.

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Black Spot

Black Spot disease appears on the leaves of trees and shrubs as small black circular spots that range in size from about ¼ inch to 1 inch in diameter. They normally appear on the upper surface of the leaf, starting in the early to mid-spring. As the disease progresses, the leaf tissue around the black spot often yellows and premature leaf drop often occurs.

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Botrytis Blight

Botrytis Blight is a common plant and tree disease that is also known as gray mold, blossom blight, bud blight or flower blight. It is caused by one of several fungi from the Botrytis species of fungus. Botrytis Blight can infect many different types of plants including ornamental trees, fruit trees, flowers, shrubs and vegetables, and the fungus, under certain conditions, can be spread between many different types of plants.

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Brown Patch

Brown Patch on grass appears as small circular patches of dead grass. The circular patches can range in size form a few inches to several feet in size. The patches are caused by a fungus called Rhizoctonia solani which attacks all types of turf grass. Brown Patch is one of the most prevalent turf disease and is most aggressive in warm, humid locations.

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Brown Rot Blossom Blight

Brown Rot Blossom Blight is a common and potentially destructive disease of stone fruit trees, including cherry, plum and peach trees, as well as ornamental flowering trees such as weeping cherry and flowering plum trees.

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Brown Rot on Citrus Fruit

Brown Rot on citrus trees appears on the fruit as light brown or dark brown spots on the skin. The spots may cover only a small part or almost all of the fruit. The markings appear as serious bruises on the fruit.

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Bud Rot

There are many pathogens that can cause bud rot of palm trees. Some of the common causes are Phytophthora palmivora, Thielaviopsis paradoxa and bacteria. Regardless of the pathogen causing the disease, the symptoms and treatment are the same.

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Cankers

There are many different types of cankers that can attack trees and shrubs. Cankers can be caused by both fungal and bacterial infections, but the control method is the same for both types of infection.

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Cedar-Apple Rust

Cedar-Apple Rust disease is a very common disease which affects cedar trees, junipers and apple trees. It is unique because in order for it to perpetuate itself, it must alternate between an apple tree and a cedar or juniper tree. It is therefore important to treat all apple trees, junipers and cedar trees in an area, regardless of whether they are yet showing symptoms.

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Citrus Scab

Citrus Scab is characterized by a large number of small raised marks or scab on the fruit of citrus trees. The leaves can also show similar brown scale- and scab- like lesions. In cases of significant infection, the fruit will not develop normally and the tree will undergo early leaf drop

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Collar Rot (Phytophthora)

Collar or crown rot is caused by a fungus that invades a tree’s lower trunk or upper roots and begins to block the tree’s vascular system. The infection point often develops as a canker which causes a girdling (strangulation) of the tree as it spreads.

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Conk on Tree Trunk

A conk or mushroom appears around the base of the tree. It is white, gray, brown or even yellowish in color and is often a hard solid growth. The mushrooms are the reproductive bodies of fungi that are growing on decaying wood. Some varieties of conk can decay the wood of a healthy tree, but normally they are found on dead or decaying wood.

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Downy Mildew

Downy mildew appears on plants and trees as small yellow spots on the upper surfaces of leaves and the underside of the leaf is covered with white, cottony growth. The yellow spots appear initially on older leaves and gradually turn brown and brittle.

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Fire Blight

Fire Blight is a bacterial infection caused by the Erwinia amylovora bacteria. It is most prevalent on the following trees: apple, pear, hawthorn, cotoneaster, firethorn and mountain ash. The bacteria overwinters on or under infected bark and in the early spring begins to ooze out.

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Fusarium Patch on Lawns

Fusarium blight or fusarium patch on lawns is caused by the soil-borne fungus (Fusarium) which during hot weather causes brown patches on lawns and turf. Fusarium blight on lawns normally attacks Kentucky bluegrass and other bluegrass varieties.

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Greasy Spot

Greasy spot is fungal disease that normally is found on citrus trees. Tell-tale signs include yellowish-brownish blister spots on leaves, often on the underside.

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Iron Deficiency

Depending on the soil in the local area, it is possible for trees to show signs of iron deficiency. The most common symptoms of iron deficiency are seen on the younger, newly formed leaves, which appear pale green or yellow. When you examine the leave you can see a distinct skeleton pattern on the leaf surface because the veins in the leaf remain green while the soft tissue of the leaf is yellow or pale green. In extreme cases of iron deficiency, the new leaves are all yellow, smaller in size or completely stunted.

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Leaf Curl

Leaf curl is a fungal disease that can attack various fruit tree varieties, but is most prevalent on peach and nectarine trees. Leaf curl is caused by the fungus Taphrina deformans. Early in the spring, shortly after the leaves emerge, the leaves appear thickened, puckered and curled and often a yellow, pink and red color.

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Leaf Rust

Rust infections are a common problem on deciduous trees. The symptoms of a rust infection can be seen as small reddish or yellow bubbles or postulants on the lower surface of leaf.

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Leaf Scorch

Leaf scorch is a common problem for many broad-leaf trees such as maples, oaks and elms during periods of hot dry weather. This is most often seen during the months of July and August.

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Leaf Spot

Leaf and tar spots can be a problem during wet weather. The spots appear as small brown or black spots on the top of leaves often developing in early to mid summer.

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Maple Wilt

Verticillium Wilt, often called Maple wilt, is a very common disease that attacks a large number of trees. It is caused by a soil-inhabiting fungus called Verticillium. The disease fungus can be spread by many methods including from plant-to-plant, through the soil, groundwater and often by infected pruning equipment that has not been properly sanitized.

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Dwarf mistletoe

Dwarf mistletoe is a parasitic plant that can infest many evergreen trees. Dwarf Mistletoe lacks a normal roots system and so relies on the host tree to supply most of its nutrients. In the summer, dwarf mistletoe spreads by discarding sticky seeds that can travel as much as 50 feet to neighboring trees.

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Leafy mistletoe

Leafy mistletoe appears on trees as a rich green leafy plant which can grow to 4 to 5 feet in size. Leafy Mistletoe is most obvious during the winter when trees naturally lose their leaves, and the mistletoe cluster becomes more evident.

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Mushrooms on Tree Trunk

A conk or mushroom appears around the base of the tree. It is white, gray, brown or even yellowish in color and is often a hard solid growth. The mushrooms are the reproductive bodies of fungi that are growing on decaying wood. Some varieties of conk can decay the wood of a healthy tree, but normally they are found on dead or decaying wood.

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Needlecast

Needlecast (or needle cast) disease is a fungal disease that attacks a variety of evergreen trees, including spruce and pine trees. When a tree is infected, it will begin to show small brown or black spots on new needle growth. The following spring the spots appear more pronounced and the needles turn yellow, brown and then drop mid-season.

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Powdery Mildew

Powdery mildew can be identified as grayish white powdery patches covering the surface of leaves and stems. There are many different strains of powdery mildew, but the basic treatment is the same for most varieties.

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Purple Blotch

Purple blotch is a fungal disease that predominantly affects onions, garlic and shallots.

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Pythium Blight

Pythium blight, also called cottony blight or grease spot, is a fungal disease of turf-grasses. All turf-grasses are susceptible to attack and the disease is most aggressive during hot, humid conditions. Poorly drained soil is also a common condition of disease growth.

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Root Rot

There are several different types of root rot that can attack, damage and kill trees including Armillaria Root Rot, Phytophthora Root Rot and Phymatotrichum Root Rot. There are also many common names for these various root rots including cotton root rot, Texas root rot, mushroom root rot, oak root rot and many other names used in various regions throughout North America.

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Rust on Leaves (Deciduous Trees)

Rust infections are a common problem on deciduous trees. The symptoms of a rust infection can be seen as small reddish or yellow bubbles or postulants on the lower surface of leaf. The rust usually appears late in the season and may cause leaf yellowing, early leaf drop and in cases of severe infections, significant defoliation throughout the tree.

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Rust on Needles (on Coniferous Trees)

Rust infections are a common problem on deciduous trees. The symptoms of a rust infection can be seen as small reddish or yellow bubbles or postulants on the lower surface of leaf.

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Scab on Fruit

Fruit tree scab is characterized by a large number of small raised marks or scab on the fruit. The leaves can also show similar brown, scale- and scab-like lesions. In cases of significant infection, the fruit will not develop normally and the tree will undergo early leaf drop.

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Slime Flux

The main symptom of slime flux (often called wet wood) is the oozing of sour-smelling sap from the tree's trunk, cracks and branch crotches. The sap is more prevalent during the spring and early summer when the tree is growing more rapidly.

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