Common Tree Diseases
Here are some tree diseases we see most often in our customer areas:
Anthracnose / Leaf Spot Diseases
Anthracnose is a common tree disease that results in extensive defoliation, shoot dieback, and twig death of your trees. It can infect a wide range of tree species, and other strains include sycamore anthracnose and dogwood anthracnose.
Anthracnose is a fungal infection, and generally occurs during extended periods of cool and wet weather in the spring. Repeated infections weaken the tree and may lead to decline and limb dieback.
Leaf Spot is a term applied to several fungal or bacterial diseases that affect the foliage of ornamentals and shade trees. Nearly all trees and shrubs are susceptible to one or more leaf spot diseases. These infections are encouraged by cool, wet weather early in the growing season.
Though unsightly, most leaf spot diseases will impact only a small proportion of the tree’s foliage, and do not seriously threaten the health of the tree. However, sometimes the pathogen spreads throughout the leaf canopy and causes moderate to complete leaf loss for a few or more consecutive years. In those cases, it can result in stunted growth, increased vulnerability to pests and other diseases, and even death.
Needle Cast Diseases
Needle cast diseases result in severe and lasting damage to many varieties of evergreen trees. Caused by several species of fungi, these diseases target Colorado blue spruce (Picea pungens), white fir (Abies concolor), several species of pine (Pinus spp.), hemlock (Tsuga), Douglas-fir (Pseudotsuga menziesii), cedar (Cedrus), and other evergreens.
Wet spring seasons with mild temperatures encourage the growth and spread of needle cast diseases. Symptoms may first appear on lower, interior branches, where needles may look purple to yellow before browning and dying.
Needle cast symptoms will gradually progress from the base of the tree towards the crown and from the interior spread to outer stems. Younger, smaller trees are at higher risk of mortality from these diseases.
Proper watering, nutrition, and pruning can help prevent infection. However, once infected, needle cast may be managed through treatments including removal of dead or dying limbs and/or appropriate preventive application of technical materials.
Blights
Diplodia tip blight is a fungal tree disease most commonly affecting Austrian pines (Pinus nigra), Scotch pine (P. sylvestris), ponderosa pine (P. ponderosa) and mugo pine (P. mugo). This tree disease will occur on well-established plantings and those already under stress.
Symptoms include stunting and browning of current year’s growth, which after several consecutive years will stunt the tree’s entire growth. Initially identified on lower branches, the blight will make its way progressively towards the top of the crown. Proper care and maintenance can help prevent infection.
Once afflicted, disease treatments can include removal of dead or dying limbs and/or appropriate preventive application of technical materials.
Fire blight is caused by a bacterium (Erwinia amylovora), and affects many members of the rose family (Rosaceae.) Apples, pears, and crabapples are its most common victims, though it can also hit serviceberries, quinces, hawthorns, cotoneasters, and many others.
The first symptoms are in early spring, when small oozing patches of dead bark, called cankers, appear on branches, twigs, or trunk. More often, the most visible sign is when the plant’s blossoms wilt quickly and turn dark just before petal-drop. This disease is so-named because its progression causes leaves and any affected fruit to wilt, shrivel, and darken while remaining attached to the branches, giving the tree a fire-scorched appearance. The ends of infected twig shoots will dry and bend into a crook shape.
This bacterium overwinters in infected bark, and is impossible to kill once it has infected the plant. Instead, the cankers are carefully pruned out in fall or winter when the trees are dormant. Then, preventive applications of technical materials can be applied to reduce recurrence.
Root Rot
Root rot is generally caused by damp conditions and poorly drained soil. Over time, this leads to weak, oxygen-starved roots that are more susceptible to fungal infection and decay. Almost all species of trees are vulnerable to root rot.
Diagnosis can be tricky, as many of the symptoms are similar to insect infestation, other diseases, or adverse environmental conditions (drought or flooding). They include:
- Slower than usual growth
- Leaves that wilt, turn yellow, or fall off
- Thinning canopy
- Dieback and decline
There are as many varieties of root rot as there are fungi that cause them. Common varieties include phytophthora root rot, armillaria root rot, and thielaviopsis root rot.
Vascular and Wilt Diseases
These tree diseases are caused by fungi or bacteria that infect the vascular tissues of trees, which are the vessels that conduct water and food throughout the plant. As the disease spreads, it interferes with the ability of the plant to obtain water and nutrients, resulting in:
- Wilting leaves
- Leaf drop and defoliation
- Limb dieback
- Tree death
Dutch elm disease, verticillium wilt, oak wilt, and bacterial leaf scorch are all common examples of vascular or wilt diseases.
Fruit Tree Diseases
There are many diseases affecting fruit trees. Although they vary by host and life cycle, the treatments are usually very similar. Blights, scabs, rots, leaf spots and rusts all occur on species of apple, pear, cherry, peach, nectarine and plum. These fruit tree diseases can affect the leaves and stems, and, of course, the fruit.
Our fruit tree treatments follow a protocol developed by several leading universities, utilizing varying products and the minimum number of treatments required to maintain tree health.
Cankers
Cankers, or stem diseases, occur when a tree has an open wound or cut that becomes infected by a fungal or bacterial pathogen. Common varieties include botryosphaeria canker, seiridium canker, volutella canker, and hypoxylon canker.
The result is a discolored lesion that may include splitting bark, oozing sap, or a strong smell. As the pathogen invades further into the tissue, it can cause:
- Small, sparse, or yellowed leaves
- Wilting
- Dieback
Cankers are most often seen on stressed trees and, if left untreated, may cause further damage and death. An arborist will be able to diagnose and address the canker without risk of spreading it. There are no direct treatments for most cankers, but they can often be managed by improving tree health through the use of fertilization and other soil amendments and improving site conditions. Preventative treatments may be available to slow the spread of the organisms that cause cankers.
Professional tree care can help you achieve sustainably healthy, beautiful trees that are an asset to your property. SavATree’s arborists are ready to help — whether you have concerns about one or more of your trees, or just want to learn more about SavATree tree care options.