Troubleshooting Tree Diseases
Trees are susceptible to a variety of diseases, and they can cause symptoms ranging from mild leaf damage all the way to killing the tree completely. In general, the best way to prevent tree disease is to keep the tree healthy, as healthy trees are able to recover from disease more easily than stressed trees.
You can prevent many fungal diseases by removing yard waste in the fall, so new leaves aren’t exposed to the spores when they emerge in spring. Since there are many tree diseases, this article will just cover some of the most common ones. Be sure to consult a professional about your diseased tree to make sure you are using the correct treatment method, as symptoms look similar for many conditions.
Foliar Diseases
Anthracnose (leaf blight)
This fungal disease attacks leaves and sometimes stems of deciduous trees such as ash, maple, hickory, walnut, and birch. Leaves appear blotchy and scorched, with some dead spots. Damage can be severe but is rarely fatal.
Rusts
Leaf rusts are common on trees such as poplar, willow, ash, birch, maples, and cottonwoods. This group of fungi are classified in the order Pucciniales, and there are around 8000 different species of rust fungi. Many of them are specific to just one or two types of host plant. The main symptom of leaf rust is the presence of yellow-orange (sometimes brown or red) powdery spots on the leaf surface. Rusts can cause leaves to drop, which affects overall growth, but they are rarely fatal.
Powdery Mildew
This fungal disease (mainly from the genus Microsphaea) causes white powdery spots on tree leaves, and is most common during the hottest and driest months of the summer. Powdery mildew can be controlled with chemical treatments if the disease is severe.
Stem Diseases
Cankers
Several types of fungus can cause cankers (for example chestnut blight, Nectria canker, Phytophthora dieback, and Cytospora canker). They occur when some damage occurs to the tree, such as a branch breaking off in a storm. This open wound allows the fungus to attack the tree during its dormant period, leaving behind areas of dead bark and wood. Some cankers are localized to a certain area, while others can spread throughout the tree with potentially lethal results. A branch with a canker can be pruned, but if the canker is on the trunk, the tree should likely be removed entirely.
Wilts
Wilt fungi (including oak wilt, verticillium wilt, and Dutch elm disease) block the water flow within a tree’s tissues, meaning that moisture cannot reach the leaves. Leaves appear scorched but don’t drop off the tree. A systemic fungicide may be effective against wilt, but often trees die too quickly for treatment to be applied.
Root Diseases
Root Rots
When fungi such as white root rot (Corticium galactinum) and Texas root rot (Phymatotrichopsis omnivorum) attack tree roots, the tree is no longer able to absorb water and nutrients from the soil. Unfortunately, it’s difficult to notice root diseases since they are underground. It is most likely in trees growing in soil that is too wet and doesn’t drain well. Symptoms are slow growth, wilting leaves, early leaf drop, and sometimes death of the tree.