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These white oak tree leaves have been infected by anthracnose. The disease causes blotchy brown spots along the leaf vein and premature leaf sagging.

How To Spot, Identify and Combat Leaf Disease on Trees

September 17, 2015

Each fall, we look forward to watching trees transform. Their leaves transition from a robust green into a speckled medley of fiery reds, oranges and yellows.

Yet, you may spot something else, too.

If your leaves have dark spots, odd colors or a distorted shape, a leaf disease could be the problem.

While you’re enjoying your picturesque landscape, scan your trees’ leaves. Spotting a disease early on leads to early treatment, so your tree can continue to wow every fall.

Look for the following worrisome signs on tree leaves.

See blotchy brown spots along leaf veins? Or sagging leaves that fall earlier than normal?

Anthracnose may be your culprit – especially if your area had a wet spring and summer. A destructive fungus, anthracnose affects ash, maple, oak, sycamore, and dogwood trees. This disease can be more prevalent and problematic due to there being multiple pathogens that cause it.

Oak leaves begin to sag while severely infected; maple leaves have large patches of white.

Spot blackened leaves that grow in a candy cane shape and, in time, turn completely brown? Or red or black pear shoots?

Fire blight could be to blame. This tree disease affects apple, pear, firethorn, mountain ash, cherry, Cotoneaster, hawthorn, and quince trees. 

Dead, blackened leaves and fruit cling to your tree, making it look burned. Flowers, fruit and twigs also shrivel and blacken, while never falling from the tree.

If you suspect fire blight, watch for small, brown cankers on twigs and branches. Also, look for cinnamon-colored twigs and shoots on the sapwood.

Notice leaves or fruit with olive green dots? Or leaves turning pale and dropping too soon?

Apple scab may be your trouble! This disease targets crabapple, apple, mountain ash, pear, and Cotoneaster trees. Initially, yellow spots emerge on leaves from May through June. They then become a dark olive green, grow larger and develop a velvety texture.

When extreme, leaves lose their color, becoming white or pale yellow, and fall prematurely.

Another telltale sign is deformed, dotted fruit and curling, new leaves.  Although mostly harmless, this is a very displeasing disease in terms of aesthetics. 

It is important to rid your yard of any debris that has fallen from affected trees. This advice is for all of these diseases.

Think your tree is suffering from a leaf disease? Call your local certified arborist

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