Spring is here, and your trees are finally leafing out for the year – but wait, what are those blotches on the leaves? Why are some of the leaves becoming distorted and curled, and even falling from the tree? Leaves aren’t supposed to drop until the fall! When people see their tree exhibiting these symptoms, it’s naturally a cause for concern, leaving tree owners worrying that their tree may be severely diseased or dying. One of the most common reasons for mottled or falling leaves is anthracnose, a fungal disease. While the symptoms seem bad, anthracnose is actually not as dangerous as one would think! Read on to find out more about this common shade tree affliction.
Anthracnose is caused by several species of fungi, whose spores infect newly formed foliage when released. The spores thrive and spread in cool, wet weather, as raindrops splash spores and facilitate their spread throughout the canopy. This causes infected leaves to exhibit a range of symptoms such as developing brown, irregular splotches, becoming deformed and curled, or falling off completely. This generally happens in spring when new leaves are forming, and can continue as long as weather conditions stay cool and wet. In most tree species, mature leaves are fairly resistant to anthracnose, and only the young, new growth is significantly affected. The fungi can survive on fallen twigs and leaves throughout the winter, repeating the cycle the following spring. Most anthracnose-causing fungi are specific to one species of tree, so fungi that cause anthracnose in a maple, for example, is unlikely to cause anthracnose in an oak.
While the symptoms of anthracnose are alarming, the good news is that anthracnose is an aesthetic problem, and won’t usually kill an established tree. Often, once the weather becomes drier and warmer in the summer, the tree will re-leaf. Occasionally weather conditions will cause the fungi to continue spreading and affecting new leaves, but for the most part the problem will subside in the summer and new leaves will remain healthy and unaffected. In certain species, such as sycamores and oaks, twigs and branches may be affected by anthracnose, forming cankers and killing off buds before leaves get the chance to form. Even these species, however, will remain healthy overall and re-leaf during the summer.
Unfortunately, anthracnose cannot be ‘cured’, but there are practices that can help prevent it from developing. Since the fungi can survive over the winter, being sure to clean out any fallen leaves, twigs, or other debris from underneath the tree can help to prevent spores from spreading in the spring. It is also important to keep your tree healthy throughout the year, as stressed trees are more susceptible to fungal disease. You can also prune the tree during the winter to thin the canopy, improving airflow and light penetration, both of which can help in preventing fungi from spreading and developing. If you notice affected twigs or branches in the spring they may be pruned off and removed from the area. When planting trees, you can also check to see which species are more resistant to anthracnose, though most species do have the potential to be affected. New Jersey has had quite a cool and rainy spring, so if your tree is currently exhibiting any symptoms of anthracnose, don’t worry too much. Trees should begin re-leafing soon as the weather gets hotter and drier. Be sure to keep your tree well watered in the meantime, prune any dead or diseased branches, and rake up fallen debris. Take comfort in the fact that while anthracnose may cause a tree to be visually unappealing for a time, the tree will be okay!