WHAT IS IT?
Phomopsis is a disease caused by a fungal pathogen known as Phomopsis juniperovora. The disease is more commonly known as Phomopsis Blight of Juniper.
Phomopsis can infect several species of cedar, firs, and juniper trees, however juniper is the genus for which the disease is best known.
The typical first symptom of Phomopsis is tip blight, or the death of the tips of newly grown needles. The new needles gradually shift from green to yellow to red to grey as the fungus kills the host branch. Phomopsis only kills new growth. If older growth begins to die off Phomopsis is not the cause. Infection typically begins to show in immature needles, while fully mature needles are resistant to the disease. If older growth does become infected during the later stages of infection, it will typically heal over time once the disease has been treated for.
The fungus overwinters in the dead shoots or stems from the previous season. Phomopsis juniperovora reproduces asexually and are spread by water during periods of heavy rain. Rain will carry the spores to new uninfected tissue, however it will not infect healthy mature twigs. P. juniperovora can produce new spores for infection in as little as three weeks during optimal conditions. Once the growing season ends the spores spend the winter in dead host tissue and the cycle begins again.
IF LEFT UNTREATED:
Except for extreme cases of prolonged infection, Phomopsis will not kill its host tree assuming that it is a mature tree. Phomopsis is capable of wiping out seedlings and immature plants however, as what happened during a major Phomopsis outbreak in the United States in the 1940s. While Phomopsis will not kill a mature host, it will stunt and kill new growth and negatively impact the aesthetic appeal of the tree.
Phomopsis is treated by a fungicide spray which is done in June.