Brown Spots on Maple Tree Leaves


Stately trees with unique leaves, maples (Acer spp.) give shade in the summer and beautiful colour in the autumn. Maples are members of the genus Acer. Even though the trees are often simple to cultivate, the presence of ugly dark spots on maple leaves may be indicative of a wide range of issues. Bigleaf maple (Acer macrophyllum) and vine maple (Acer circinatum), both of which are native to California and grow well up to U.S. Department of Agriculture plant hardiness zones 8 or 9, depending on the species, according to Cal Poly, are two of the approximately 125 species of maples that exist. Bigleaf maple (Acer macrophyllum) and vine maple (Acer circinatum) are both examples of maples. Finding out what causes the brown patches on the leaves of maple trees is helpful in maintaining the plants’ health.

Anthracnose Fungal Infection

Anthracnose is a fungal illness that is transmitted from tree to tree by the splashing of water, such as when it rains or when maple trees are watered incorrectly. Infections caused by anthracnose, which are also known as leaf, twig, and shoot blight, are more likely to occur following periods of heavy spring rain when there is new growth present. The condition results in the appearance of tiny patches that might be brown, black, or tan. The illness may cause the leaves to fall off prematurely, and it can even spread to the branches. The webpage for the Statewide Integrated Pest Management programme at the University of California states that anthracnose is seldom lethal and that fungicides are not recommended for treating it.

The accumulation of fallen leaves and twigs, followed by their removal from the yard and disposal elsewhere, may help prevent the spread of illness. The optimal time to prune a tree or shrub to increase air circulation in the canopy and make the leaves dry more rapidly is in the winter. Infections caused by anthracnose may be avoided by using appropriate watering techniques on maple trees, such as avoiding wetting the foliage or the trunk of the tree, increasing drainage, and nourishing the tree after the leaves have opened to improve the tree’s vitality.

Bacterial Leaf Spot

According to Kansas State University, this disease is brought on by Pseudomonas syringae and manifests itself on the leaves of maple trees as irregular brown blotches. Following heavy spring rains is a common trigger for bacterial leaf spot, just as it is for fungal infections. Laboratory testing is the only method that can definitively determine if spots on maple leaves are the result of a bacterial or a fungal infection. Pruning away branches that are seriously diseased and improving air circulation inside the canopy are two of the steps that need to be taken. Additionally, you should avoid overhead watering and over-fertilizing the maple tree. The tree will often recover from the bacterial leaf spot as long as the disease does not extend to the trunk.

Fungal Leaf Spots

On maple tree leaves, the fungus Phyllosticta spp., Spilocaea and Venturia spp., and Rhytisma spp. are responsible for anthracnose as well as a number of other types of leaf spots. Spots might be very tiny and round, or they can occur in patches that extend throughout the leaf’s surface. It is easier to prevent the spread of illnesses by adhering to proper sanitation procedures, such as removing plant waste from the ground near the maple tree and disposing of it away from the yard. According to the University of California Integrated Pest Management, increasing the air circulation around the tree and avoiding watering the tree from above are two ways to help prevent fungus from damaging the tree.

Maple Tree ‘Bugs’ From Oaks

In most cases, the foliage of maple trees is the sole target of the disease known as Sudden Oak Death (SOD), which causes brown blotches on the leaves. This disease is especially prevalent in coastal California. This disease is far less harmful to maple trees, but it has the potential to spread to surrounding oak trees and destroy them. Clean and disinfect the pruning instruments, then cut away any contaminated growth. If you live in an area that has a quarantine in place to prevent the illness from spreading to places that are not afflicted, you should examine the local legislation regarding the disposal of plant waste that is sick. In most cases, maple trees are able to recover on their own.

Cultural and Environmental Problems

It is possible for the leaves of the maple tree to become misshapen, discoloured, or speckled as a result of deficiencies in the soil in which the tree develops. It is more likely that a deficiency in nitrogen or iron, either in the soil or in the capacity of the maple tree to take up and utilise the minerals in the soil, is the cause of the issue than “bugs” that affect maple trees. A test of the soil may assist in determining which nutrients are missing from the soil. According to the Integrated Pest Management programme at the University of California, soggy or diseased roots, as well as nematode infestation in the soil, are examples of cultural issues that might interfere with a tree’s capacity to absorb nutrients. Fertilizers with a controlled release or foliar sprays might be helpful in mitigating the issue.