There are many reasons a juniper might turn brown. Fungal tip blights, cankers, mechanical damage, and salt injury are some of the most common causes.
Several juniper samples with tip blight were submitted to the Plant Disease Clinic this spring. Phomopsis and Kabatina tip blights are two common diseases of juniper. Kabatina tip blight generally appears in February and March. Phomopsis tip blight shows up later, from April through September.
Symptoms are similar for both diseases. Affected needles turn reddish-brown to gray. The fungi can girdle branches causing the tips to die. Small, black fungal fruiting structures, called pycnidia, develop on diseased leaves and branches. They often can be seen with the naked eye.
Management includes pruning out diseased branch tips when the plants are dry. This will prevent fungal spread. When creating new plantings, provide adequate space between plants to allow for good air circulation and sun exposure. Choose disease resistant varieties when possible. Fungicides are an option, but are rarely necessary in established plantings.
Junipers with fungal cankers, commonly caused by the fungus Botryosphaeria stevensii, often have entire branches that die. This symptom can look like it was caused by mechanical injury, for example if a branch breaks near the main stem. Water can't get to the tips and the whole branch turns reddish-brown and dies. Pruning out dead branches may or may not effectively manage Botryosphaeria canker. There aren't any fungicides labeled for Botryosphaeria canker on juniper.
Rock salt, used to melt ice, frequently causes junipers to turn brown. Salt damage usually occurs along walkways and roads. The damage typically appears uniformly on one side of the plant. Once again, it's best to remove any brown branches to prevent the build up of fungi that like to feed on dead plant material.
The Iowa State University bulletin Pm-1702, Juniper Diseases, is available from your local county Extension office or from the Iowa State University Extension Distribution Center. Contact the Distribution Center at: 119 Printing and Publications Building Iowa State University Ames, Iowa 50011-3171 Telephone: (515) 294-5247 Fax: (515) 294-2945 https://store.extension.iastate.edu/
This article originally appeared in the May 10, 2002 issue, p. 61.