By: Liz Baessler
Black leaf spot, also sometimes known as shot hole disease, is a problem that affects all stone fruit trees, including cherries. It isn’t as serious on cherries as it is on some other fruit trees, but it’s still best if it’s avoided. Keep reading to learn more about how to manage black leaf spot and shot hole disease on cherry trees.
Cherry black leaf spot is a disease caused by the bacterium Xanthomonas arboricola var. pruni, also sometimes referred to as Xanthomonas pruni. It affects only stone fruits, and while it is most common on plums, nectarines, and peaches, it is also known to affect cherry trees.
Cherry trees that fall victim to black leaf spot first exhibit symptoms as small, irregularly shaped spots of pale green or yellow on the undersides of leaves. These spots soon bleed through to the upper side and darken to brown, then black. Eventually, the diseased area falls out, earning the disease the name “shot hole.”
There may still be a ring of affected tissue around the hole. Often, these spots cluster around the leaf tip. If the symptoms become severe, the whole leaf will drop from the tree. Stems may also develop cankers. If the tree becomes infected early in the growing season, fruit may develop in strange, distorted shapes.
Though the symptoms may sound bad, cherry shot hole is not a very serious disease. This is good news, because there does not yet exist an effective chemical or antibacterial control.
The best method of prevention is to plant trees that are resistant to the bacterium. It’s also a good idea to keep your cherry trees well fertilized and watered, because a stressed tree is always more likely to succumb to a disease. Even if you do see signs of infection, however, it’s not the end of the world.
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Cherry Shot Hole Disease Symptoms. Photo: University of Maryland Extension / Ask an Expert
White Prunicola Scale on Cherry Laurel: Photo: University of Maryland / Ask an Expert
Prune out any dead or dying branches. If the infestation is not heavy, use a soft brush to brush away the white scale covers from the branches. During the growing season, wrap a piece of double-sided tape around one of the branches. This is a test to monitor the active crawler (juvenile) stage of these insects. They are more susceptible when they come out in May/June depending upon temperature and there may be several generations per year. When you see crawlers sticking to the tape, that is a good time to apply horticultural or insecticidal soap according to label directions.
Winter Injury of Cherry Laurel. Photo: Elizabeth Bush, Virginia Polytechnic Institute and State University, Bugwood.org