Wet weather invites fungal infections of all types. Some fungal diseases can sit dormant for years waiting for the right conditions to develop and spread. With the drought over and the rain having returned, it’s time to take a look at your trees and assess if you might have a problem.

Even though most fungicide treatments for the following issues would begin in early spring, it’s not a bad time to remove any diseased fallen leaves. This will help prevent the spread of the fungi to other trees. Fall is the perfect time to start combating what’s already taken hold.

Check out the list below to learn about possible diseases and how you can take action.


Tar Spot

This one has been a big concern for residents this year. If you have Norway maples, then you have definitely seen your trees grow large dark spots. A lot of the leaves are even browning and shedding early. This is the tar spot fungus. While it can affect maples in general, you often see that Norways are very susceptible. There is really no effective way to treat this disease. The good news is that it’s cosmetic and will not kill the tree. The best thing you can do is gather and destroy all the spotted leaves. This will prevent the fungus from spreading to other nearby trees.



This is another one that is unattractive, but also not deadly. Leaf galls can be caused by both insects and fungi. Galls on leaves are nothing to worry about, but you should get a consult if you see any abnormal structures on branches and twigs as this can impact the circulatory system of the plant. Sprays are only good in the preventative sense and raking up infected leaves in the fall can prevent spreading.


Powdery Mildew

Powdery mildew is pretty easy to identify. This minor disease can can cause early defoliation of leaves and can be a sign of more disease at play within the plant. Just like people, a woody plant can start contracting more than one illness once initially weakened by something like drought stress, winter damage, or a deadly disease. Usually, powdery mildew can be unattractive at worst. Pruning out infected twigs and leaves definitely helps and controlling sprays can be given throughout the warm seasons.


This one affects fruiting trees. Orchards fear the scab for reducing their yields and bringing down quality of the fruit. So cherries, apples, and pear trees are adversely impacted. Other trees that suffer scab are willows, poplars, and cotoneaster. Look for dull black or grey-brown lesions on the surface of tree leaves, buds or fruits. Spray fungicides in early spring right as the buds break open.


Needle Cast

This disease happens to needled evergreens like pines, firs, and spruces. It causes browning of the needles and defoliation. Take look at the image below to see the disease on an individual needle. Norway spruces are more resistant.

Fungicide needs to be sprayed when the needles are half-elongated spray and again when needles are fully elongated.

Dutch Elm Disease

This is a deadly disease and is actually spread by a bug. Elm bark beetles burrow into the tree carrying the fungi. Whole branches in the tree will start to yellow and die. You must prune infected areas and destroy as soon as you notice the issue. Systemic and injections are available to combat the disease, but if the tree dies it’s best to remove the tree immediately and plant something else.



Infected trees include maples, horsechestnut, dogwoods, euonymus, ash, walnut, sycamore, and oaks. Look for signs of premature defoliation, dead branches, bud death, and brown dead spots on leaves near margins and along veins.

This disease varies among different types of trees and causes gradual weakening of the tree’s vigor. Must be sprayed when buds break in spring. More than likely need several applications. Remove and destroy fallen leaves to prevent spread of disease to other trees.