Answer: Arbutus unedo is subject to a few diseases, but symptoms include black spots on leaves, complete defoliation, or gradual decline. Sudden decline is usually associated with environmental or cultural problems. Poor soil drainage over a wet winter can suffocate roots but the problem may not show up until the following growing season. You may want to dig around the roots of the ailing tree to see how things look below ground. Healthy roots will be creamy white inside; dead roots will be brown or rusty colored. Mushy roots indicate root rot. You may also want to take a sample of a leafy branch to your local Extension Office. Agents there can look at the leaves under a microscope to check for disease pathogens. Wish I had more to offer!
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