If you have ventured out into your yard and noticed that your leaves look like someone has shot them with a BB gun, don’t worry. The culprit is a fungus known as Wilsonomyces carpophilus, commonly known as Shot Hole Disease or Coryneum Blight. While it may seem that insects or armed squirrels have turned your garden into a tiny firing range, it is the fungus that eats away at leaves and fruit, causing holes and spots. It affects fruit trees as well as some flowering edible and ornamental plants. The fungus is generally not fatal to the plant but can seriously reduce fruit yield. Heavily infected plants may start to drop their leaves during the mid-summer months.
Shot hole disease thrives in wet conditions. The disease is most noticeable in spring, as new growth is most susceptible. “Shot hole fungus commonly overwinters inside the infected buds, as well as twig lesions, where the spores may thrive for several months¹”. Shot hole disease symptoms become visible in late spring. Lesions will appear on new buds and shoots giving them a reddish or purplish-brown color. Eventually, these spots become larger, turning brown and falling out—giving the appearance of gunshot holes in the leaves. Eventually the leaves will drop. The stress also affects the tree’s ability to fruit. The fruit that does survive will present with spotting on the upper surface that may even become rough with a rotted appearance.
If you suspect that your plants may be suffering from shot hole disease, you should call your arborist right away. Fungicide treatments are very effective at suppressing any outbreak that could be infecting your plants. Treatment in the fall, before the winter rains, is the most effective way to treat and suppress any infection. Also, overhead watering is strongly discouraged. Make sure to angle sprinklers low enough so as not to wet the canopy of your trees. Organic treatments are also available.
So as always,