Tree Diseases and Disorders

Common Tree Diseases

Heart rot

Heart rot is a disease caused by the fungus Fomes pini. The fungus spores that cause heart rot are windborne and enter the tree through old dead branch stubs left on the tree. The signs of attack are the presence of sporophores on the trunk. The sporophores can be large shelf like sporophores up to eight inches across or smaller bracket like sporophores. The sporophores are usually gray or brownish black with a white margin. The disease is not deadly but slowly destroys the heartwood leaving the tree more susceptible to failure. Consult with a professional if you observe sporophores on the trunk.

Juniper Blight

A disease caused by the fungus Phomopsis juniperovora, infects southern red cedar, Italian cypress, arborvitae and many ornamental junipers. The signs are blight (dieback of foliage) on the tips of the branches causing the foliage to turn reddish. The disease advances into the stem killing the xylem tissues. The infection occurs usually during spring when warm wet weather is prevalent and the plant is adding new succulent growth. It has similar symptoms of spider mite damage and consequently the plant should be checked by a professional to determine the treatment. Sometimes the plant is being infested by juniper blight and spider mites simultaneously. An approved fungicide can control this disease.

Pitch Canker

A disease caused by the fungus, Fusarium lateritium, shows up as dead branches in the crown of our native pine trees. The fungus does not produce a sporophore but if the bark is peeled away from the canker (dead stem tissue usually discolored and shrunken) the xylem will be soaked and stained with resin. The spores of the fungus enter the tree through wounds and infect the tissue. Chemical control is not recommended. Try to prevent unnecessary wounds on your trees.

Foot Rot of Citrus (Also commonly referred to as collar rots and bleeding cankers)

Several fungus species of the genus Phytophthora are soil borne pathogens that infect the root collar or roots of Citrus trees. The fungus causes cankers to appear on the root collar and lower trunk. The cankers are reddish brown to brown in color. The cankers will ooze a brownish liquid. Over time the canker will dry and crack exposing xylem wood that is stained. The damage to the root collar area disrupts the vascular flow and causes dieback in the upper crown. Ultimately this disease can kill the citrus. Phytophthora can enter through wounds in the basal area so it is important not to allow wounds to occur on the thin skinned citrus. Keep a large ring around your citrus and do not allow mulch to contact the trunk. Do not wound with a hoe or string trimmer. A recommended systemic fungicide can help control Phytophthora if treated early.

Hypoxylon Canker

Hypoxylon canker (there are several species of Hypoxylon) is a fungus disease that can attack all species of oak trees that are severely stressed and ultimately causes their death. It is particularly damaging to drought stressed trees but also infests trees stressed by heat, root injury, herbicides or other diseases. Hypoxylon does not infest tree with good vitality. Hypoxlon invades the bark of the trunk and larger branches and colonizes within the inner bark, sapwood and cambial area. Its presence disrupts the tree’s vascular system causing death. The first signs of Hypoxylon are when the bark sloughs off revealing the grayish black fungus mats that developed under the bark. Hypoxylon is always present in oak trees in a latent form and can quickly invade if the tree becomes stressed. Keep your trees healthy and watered to avoid this killer.

Mushroom Root Rot

There are several fungi that infest roots and cause tree decline and death. Mushroom root rot is one of the most common and is caused by the fungus Armillaria tabescens. Mushroom root rot infects both conifer and hardwood species. Mushroom root rot is an opportunistic fungus that typically infects trees that are stressed and weakened. The fungus destroys the wood in the roots and can advance into the root collar area. The crown of infected trees may thin and have leaves that are small and chlorotic. In the late summer and fall the fungus will produce clumps of small tan mushrooms that are 1″-3″ in diameter and visible protruding from the grade. The mushrooms are attached to lateral roots close to the surface and the flare roots. A tree with mushroom root rot will ultimately die but before it does it is susceptible to wind throw.

Oak Leaf Blister

Oak leaf blister is a very common leaf surface fungus disease that alarms homeowners almost every year. The fungus (Taphrina caerulescens) causes large discolorations or a blister on the leaves of its favorite hosts the laurel and water oak. The blister appears as a reddish or blown splotch on the leaf. The blistered area is necrotic (dead) tissue. Cool wet springs cause a proliferation of this fungus. Mild infections are barely noticed as the blisters are small and confined to a relatively low percentage of leaves. But a severe infestation can cause the entire tree to defoliate and cause homeowners to believe that there tree is dying. Tree death from oak leaf blister is extremely rare and happens only after several years of severe infestations. Because this disease is rarely harmful and as it covers most of the crown, control is not recommended. If you have a tree with high ornamental value an approved fungicide will control the blister.

Sphaeropsis Knot

A serious disease that is killing the East Palatka holly (Ilex x attenuata ‘East Palatka’) tree in Florida. Once infected the tree may die within five years. Early signs include galls (swollen areas on twigs) on twigs and sometimes the effect known as “witch’s broom”, the proliferation of twigs emanating from a gall. The foliage at the tips of branches will first appear chlorotic and later will die. The disease will spread to the larger branches and ultimately kill the tree. There is no verifiable prevention or treatment for Sphaeropsis knot at this time. It can be spread through pruning tools, so pruning tools should be sanitized after use on an infected tree. Sphaeropsis Knot infects oleander, citrus and bottlebrush to a lesser degree.

Sycamore Anthracnose

Anthracnose of the sycamore tree is caused by a fungus and appears as scorched splotches on the surface of the leaves. Repeated infestations can weaken the branches to the point that die-back occurs and the tree can become susceptible to borers and other pathogens. Leaves should be treated with an approved fungicide prior to bud break with follow up applications.

Leaf Spot

Leaf spot appears as a small discolored (usually brown or black) circle of dead tissue on a leaf surface. A single leaf may have a few or several of these spots. Leaf spot can be caused by a variety of fungi and some bacteria. The spores of leaf spot fungi that infect plants are disseminated through wind currents or are borne in raindrops that splash off infected leaves. Leaves that stay moist or grow in the shade are most susceptible. Leaf spot rarely causes serious damage to the host tree and consequently control is not recommended. In severe cases samples of the foliage should be analyzed to identify the specific pathogen and the proper fungicide apply. If you have a serious leaf spot infestation consult with a horticultural agent with the County Cooperative Extension Service.

Botryosphaeria Canker

This canker is caused by the fungus Botryosphaeria dothidea and attacks many tree and shrub species but has been particularly damaging to the camphor tree. The fungus is an opportunistic pathogen that typically infests trees that have been weakened by environmental conditions such as drought or physical damage such as mechanical root loss or over pruning. Camphor trees planted on sandy soils are very susceptible as they readily suffer from drought stress during extended dry periods. Typical symptoms are branch die-back. The fungus kills sapwood tissue causing cankers (areas of dead tissue) – to appear on stems. The disease will progress inward until the entire branch is killed and finally the whole tree. The spores of the fungus often enter through open wounds. One source of prevention is to remove branches infected with cankers back to the branch collar (make a proper collar cut). If you remove a branch infected with the canker, be sure to sterilize the pruning tool blade with a disinfectant such as Lysol, 10% bleach or 70% denatured alcohol. The best prevention for Botryosphaeria canker is to water trees during drought events, avoid over pruning and do not subject the tree to mechanical root damage. Some other tree species affected by the canker include: sycamore, magnolia, wax myrtle, hickory and sweet gum.

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