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The disease is most severe in nursery stock and seedlings where plants are grown closely together. However, established plants are also attacked. Two different fungi have been found causing this disease Phomopsis juniperovora and Kabatina juniperi. Microscopic examination of the diseased tissue and fungal spores is required to determine which fungus is present.
Phomopsis attacks the foliage and then invades stems anytime during the year. Branches up to 0.4 inch (1 cm) in diameter can be girdled. From the time a twig is first infected until new spores are formed can be as short as 3 weeks. At moderate temperatures (16-26oC = 61-79oF) when the foliage is wet, a spore can germinate and invade the needle in 7 hours.
Blight due to Kabatina occurs in the spring. It is suspected that the actual infection occurred the previous fall. In controlled experiments, only plants with wounded foliage become infected. In nature, insect feeding sites may provide the point of entry.
Prepared by Gary W. Moorman, Professor of Plant Pathology
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