Juniper Twig Blight

Junipers (Juniperus sp.), also known as red cedars, are susceptible to a disease that results in the death of twig tips. 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.

Symptoms

• In the spring, the light-green developing foliage turns brown at the tips of small branches.
• Dead foliage may turn tan or ash gray with small black dots (spore-forming structures) in the dead needles.
• Cankers (sunken dead areas) form at the junction of the living and dead parts of the twig.

Phomopsis juniperovora

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 (16-26 degrees C = 61-79 degrees F) when the foliage is wet, a spore can germinate and invade the needle in 7 hours.

Phomopsis Twig Blight Management

• Do not purchase plants with dead or dying twigs.
• Plant junipers in areas where air circulation will allow the foliage to dry quickly after dews, rain, or sprinkler irrigation. Do not crowd plants. Avoid sprinkler irrigation if possible.
• Plant resistant varieties:

  Juniperus chinensi (Chinese juniper)

  fimina, Iowa, keteleeri, pfitzeriana aurea, rubusta, sargentii, sargentii glauca, shoesmith

  J. communis (Common juniper)

  aureo-spica, depressa, hispanica, hulkjaerhus, prostrata aurea, repanda, saxatilis, suecica

  J. horizontalis (Creeping juniper)

  plumosa, plumosa aurea, procumbens

  J. sabina (Savin juniper)

  broadmoor, knap hill, skandia

  J. squamata (Western red cedar)

  campbellii, fargesii, prostrata, pumila

  J. scopulorum (Western red cedar)

  silver king

  J. virginiana (Red cedar)

  tripartita

• Prune out infected branches during dry weather.
• Apply thiophanate methyl (Clearys 3336* or Domain FL*) or azoxystrobin (Heritage*) whenever new growth begins and conditions are wet. Spring and fall growth must be protected. Pruning at other times may also stimulate new growth. Sprays are not required during dry weather.

Kabatina juniperi

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.

Kabatina Blight Management

• Water and care for plants to promote good vigor and to prevent damage to the foliage.
• Protect plants from insect attack.
• Prune out infected branches during dry weather.
• The Dithane*, Mancozeb*, or Zyban* may assist in control if applied in late summer and fall.

*Trade name

References

Hartman, J. 1982. "Juniper diseases." In Diseases of woody ornamental plants and their control in nurseries. R. K. Jones and R. C. Lambe, eds. North Carolina State University Agricultural Extension Service AG-286. pp. 60-61.

Peterson, G. W. 1981. Pine and juniper diseases in the Great Plains. USDA Forest Service General Tech. Report RM-86. Pp. 37-40.