Juniper Tip Blight
By Dr. Sharon M. Douglas
Department of Plant Pathology and Ecology
The Connecticut Agricultural Experiment Station
123 Huntington Street
P. O. Box 1106
New Haven, CT 06504-1106
Telephone: (203) 974-8601 Fax: (203) 974-8502
Tip blight and dieback of twigs on juniper, and more rarely on arborvitae, hemlock, true fir, and Douglas-fir, can result from any of several causes, biotic (living) and abiotic (nonliving). This problem is sometimes less serious as plants become older, although it can be found on established plants, especially those growing under crowded or stressed conditions.
SYMPTOMS AND DISEASE DEVELOPMENT:
Tips of branches affected by this problem turn brown or ash-gray and often show progressive dieback. In extreme cases, the entire plant is killed. Abiotic causes of tip blight include winter drying and injury, drought, or other environmental stress. The biotic organisms associated with tip blight are the fungi Phomopsis and Kabatina. Phomopsis typically infects newly developing foliage in spring and gradually moves into the stem. Symptoms develop on the current year’s foliage and are often evident by midsummer. Kabatina typically attacks wounded, year-old twigs and symptoms usually show up when the foliage begins to regain its seasonal color in spring. Kabatina appears to require a wound, usually associated with insect activity, whereas Phomopsis is capable of directly penetrating healthy tissue. Phomopsis and Kabatina can overwinter in fruiting structures on infected twigs and both fungi may be present on affected shrubs.
In advanced stages of tip blights associated with fungi, small, black fruiting bodies can be found at the base of blighted twigs. However, twig death from abiotic causes can sometimes appear the same as the fungal-associated blights since fruiting structures of some saprophytic fungi (ones that colonize dead tissues) look like plant pathogens (fungi that cause disease). Therefore, the first step to an effective management strategy is to accurately identify the cause. Microscopic examination is necessary to distinguish Phomopsis from Kabatina. In some cases, there is a sharper line of demarcation between blighted and green tissue in twig blights from biotic than from abiotic causes.
Control can be accomplished by following a multifaceted approach. Regardless of the cause, dead tissues should be pruned and removed from the area. Pruning should be done when the foliage is dry. When watering, avoid overhead irrigation and wetting the foliage or water early in the day to encourage rapid drying. New plantings should be spaced to provide good air circulation. Pruning of older plantings can help to reduce tip blight by improving air drainage and foliar drying. It is also important to avoid wounding during transplanting and cultivating. Plants should be kept as vigorous as possible by fertilizing, controlling insect infestations, and watering during any periods of drought. Since resistant cultivars are available, they should be considered for use and many species of juniper have been reported to be resistant to at least one of the tip blights. For example, Juniperus chinensis cultivars "Femina" and Pfitzeriana" and J. comminus cultivars "Depressa" and "Saxatalis" are reported to be resistant to Phomopsis. J. chinensis "Hetzii" and J. communis "Hibernica" are resistant to Kabatina. Additionally, some cultivars are resistant to both fungi and include J. chinensis "Keteleeri" and "Pfitzeriana."
Fungicide applications can supplement other control strategies if the cause is biotic. For control of Phomopsis, the fungicides thiophanate methyl and thiophanate methyl plus mancozeb are registered for use. Sprays should be applied when new growth begins to emerge in the spring, with follow-up applications at 7- to 10-day intervals (or according to label instructions) or until new growth is mature and dark green. Kabatina can be controlled with the fungicides mancozeb or thiophanate methyl plus mancozeb. Applications typically begin in midsummer and continue when conditions are favorable (wet, cool, and cloudy). Since it is not uncommon for a plant to be infected with both fungi, the combination product of thiophanate methyl plus mancozeb will control both diseases. All fungicide labels will contain information on dosage rates and safety precautions.
Tip blights and diebacks of twigs of juniper as well as arborvitae, hemlock, true fir, and Douglas-fir can result from many causes. Abiotic (nonliving) factors contributing to damage include winter injury, drought, and other environmental stresses. Biotic (living) organisms are also associated with tip blights and include the fungi Phomopsis and Kabatina. This fact sheet discusses the symptoms, spread, and management options to minimize the impact of these problems in the landscape.