Junipers are particularly susceptible to Phomopsis and Kabatina tip blight, two damaging fungal diseases that cause needle browning and dieback at the tip of the branches. Tip blight of junipers is caused by two different species of fungi, Phomopsis juniperovora and Kabatina juniperi, which cause similar symptoms in the affected plants. However, the two diseases differ by the time of the year when they occur and their development on the plant.
Phomopsis tip blight usually appears from middle April through September and causes the new growth at the tip of the branches to turn dull brown and finally ash-gray. Often, small lesions appear around the twig. Minute black spots may be observed on the lesions; these are the fruiting bodies or spore producing structures of the fungus. The spores are dispersed by splashing or wind-driven rain. Usually Phomopsis spores infect new foliage tissue during spring (April-early June) and late summer (late August through September) under favorable environmental conditions such as high humidity. Even though Phomopsis tip blight may damage branch tips and slow down plant growth, it seldom causes death of the plant. Death, however, may occur if the affected plant has experienced extensive damage and stunted growth due to blight early in the season.
Phomopsis tip blight can be particularly devastating in nursery settings when it affects seedlings of young grafted stocks. Otherwise, the damage it causes on junipers in natural or landscape settings is not very significant.
Symptoms of Kabatina tip blight appear earlier in the year, usually during February and March. This disease also affects the branch tips, which in this case change color to yellow or brown. The affected tissues on the twigs show an ash-gray coloration and, like in Phomopsis tip blight, are covered with small black fruiting bodies where spores are produced. Later in the spring (May-June), the affected foliage drops, but no further infection occurs until later in the fall months, when Kabatina spores may infect wounded or damaged tissues of juniper branch tips. The blight symptoms will then be visible early the following spring.
Both blights are more prevalent in moist and warm conditions. Whenever possible, resistant varieties should be planted to prevent these diseases, and healthy practices implemented. These include adequate spacing between plants to allow for sufficient air flow, avoiding prolonged night time watering or using overhead sprinklers, and pruning and discarding any diseased material. Plants are particularly susceptible to tip blight infection when stressed or wounded by insects or mechanical injury.
Both blights, in general, do not require any chemical control in natural established plantings. For more information on these diseases and for a list of resistant juniper varieties, refer to Pm-1702, available from your local county extension office or the Extension Distribution Center, 119 Printing and Publications Building, Iowa State University, Ames, Iowa 50011-3171, Telephone: 515-294-5247, Fax: 515-294-2945, or by E-mail: firstname.lastname@example.org.