Arbor-wellness: Anthracnose
Why are the leaves falling off my trees when they just leafed out? If you have sycamore trees, dogwood, Modesto ash or certain oak trees, they may be suffering from Anthracnose. This is a leaf disease affecting these tree types and a few others. The leaves are infected when they first come out, but the disease spreads and gets worse as the leaves mature. About the time your tree should be producing shade and capturing sunlight for energy production, the leaves die and drop off, creating a mess on the ground. On some trees, like the sycamore, the disease can affect the small twigs as well. Thus, you often see small and medium sizes twigs falling off these trees throughout the summer. 
Will this kill my tree? While anthracnose in and of itself does not kill a tree, it weakens the tree which allows other insects or diseases to attack the tree more readily. This happens because fewer leaves on the tree means it is not producing enough energy to make the auxins and other chemicals needed for tree defense. The tree also has to expend extra energy to put out new leaves, which often come later in the spring or in early summer.
Why do my trees have this problem? Anthracnose likes cool moist weather, so a prolonged cool spring, with rain, fog or other moisture encourages the development of the disease. One good thing about this disease is that it is typically host specific, meaning that the anthracnose on your sycamore will not infect your maple trees.
What can I do about it? The best way to discourage anthracnose is to make sure your trees are healthy and are pruned properly. Water properly – deep, infrequent watering throughout dry times, encourage proper growth with good nutrition and soil health (we usually recommend an organic based feeding that does both of these things), mulching to reduce water loss and tree stress. If your trees can benefit from treatment, it is best to start in the fall or early spring before the leaves come out. Sometimes multiple treatments are best, depending on the weather and the type of tree.
If you are concerned about anthracnose and want to schedule an inspection, fill out the form below.