Is your willow tree looking a bit worse for wear? There are two diseases that are common in willow trees in North America: willow scab and black canker disease. The two cause similar symptoms, but it is usually possible to tell the difference if you examine the tree closely.
Black Canker of Willow
Many trees are susceptible to various canker diseases, but the strain of fungus that causes black canker disease in willows only infects various species of willows – not other tree varieties. Weeping willows are generally resistant to the disease, so if you have a weeping willow, chances are good that it's symptoms are due to willow scab rather than black canker.
The early symptoms of black canker include brown to black lesions on the leaves and twigs. These lesions are irregularly shaped with jagged edges. As the disease progresses, the cankers grow larger and deeper, and they begin to form on larger branches. It's important to have the disease treated early while the cankers are still small. A tree care expert can trim off the affected branches and cut out any infected portions of the trunk or large branches. Fungicides can be applied to the branches that remain.
When black canker disease is caught early, it can often be kept under control with periodic pruning and treatment with fungicides. However, it is difficult to cure entirely.
Willow scab is also caused by a fungal species that only affects willow trees. Both weeping and non-weeping willow varieties are susceptible. The symptoms are similar to those of willow canker, but the spots that appear on the leaves tend to be round and brown, rather than irregularly shaped. They first appear in the spring and then turn olive green in color as the season progresses.
Willow scab does not always progress to the point of causing cankers on the tree, but if a tree is weakened by other subsequent infections, it may. The cankers caused by willow scab tend to be small and dry, whereas those caused by black canker are larger and moist.
Generally, willow scab is not a threat to a willow tree in and of itself. However, it does weaken the tree and make it more susceptible to subsequent infections, which for non-weeping willows include black canker disease. Thus, it's important to have willow scab treated by an experienced arborist. Generally, removing the affected branches is sufficient; fungicides are rarely required.
It is not uncommon for non-weeping willow varieties to develop both willow scab and black canker disease at the same time. If you cannot tell which disease your tree's symptoms more closely resemble, it probably has both. Prompt treatment is especially important in this case, since the combination of the two diseases can lead to tree death within a few years.
Contact professionals like Outdoor Solutions Landscaping for assistance.