Juniper tip blight is caused by one of two different fungi, Phomopsis juniperovora or Kabatina juniperi. Diseases often enter through wounds, like spider mite infestation.
Symptoms of the two diseases are identical; however, some aspects of their control differ. Therefore, correct identification of the causal agent is important. These fungi can also attack other hosts, including Cryptomeria, Chamaecyparis, and Thuja species. They seldom cause significant damage in landscapes unless weather conditions become favorable for disease development. However, they can be very destructive in seedbeds, cutting beds, and lined-out stock in nurseries.
Visible symptoms include browning and dieback of young needles and shoot tips. Gray lesions usually girdle the shoot at the base of the dead tissue. Tiny, black or grayish fungal fruiting bodies may be visible in the gray lesions. On highly susceptible hosts, the fungus may invade and girdle larger stems, resulting in browning and death of major branches; however, this degree of disease severity is rare. Both Kabatina tip blight and Phomopsis tip blight are most damaging on younger plants.
Symptoms of tip blight diseases can be easily confused with damage from either of two different insects, the juniper midge or the juniper tip midge. Both insects deposit their eggs inside young juniper shoots. The developing larvae mine the inside of the shoot and cause death of shoot tips. If affected shoot tips are carefully examined with a hand lens, small holes can be seen where the adult insect exited the shoot. These holes distinguish this type of damage from Phomopsis or Kabatina tip blight.
Kabatina Tip Blight
Kabatina juniperi produces its spores in the fall, but symptoms do not appear until late winter or very early spring. Unlike Phomopsis juniperovora, Kabatina juniperi infects through wounds caused by insects or mechanical damage. It does not invade healthy twigs.
Phomopsis Tip Blight
During prolonged wet, cool periods in spring or fall, spores of Phomopsis juniperovora ooze from black fruiting bodies and are spread by splashing rain or overhead irrigation to other branches and adjacent healthy plants. Spores of this fungus can be produced throughout the summer, but most infections occur in spring and fall. Fungal spores germinate and invade young, healthy twigs. Older twigs are resistant to infection. The blight fungus penetrates young tissues rapidly and may kill first-year seedlings.
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