Phomopsis is a fungus that causes shoot blight and twig cankers. The disease is most common among junipers.
Phomopsis may also affect other evergreen ornamentals and a few deciduous trees. This may include American and Oriental arborvitae, hinoki cypress, English yew, Douglas fir, true fir, hemlock, European larch, redwood, white cedar and jack pine.
The fungus first affects foliage, then spreads to and sometimes kills stem tissues. It may eventually kill the plants.
Signs and Symptoms
Look for die-back of the new shoot growth (tip blight). Small yellowish spots appear on young needles within a few days after infection. The new growth changes from light yellow green to reddish brown to ash gray as it dies from this fungal disease.
Phomopsis starts on immature scale leaves or needles. It only kills new growth. Mature needles are resistant. If more than just the new growth is killed, other fungal diseases or environmental injury is involved.
When the fungus invades young stems, it may girdle them if they are less than one third inch in diameter. The portion of the seedling above the girdled area then dies. The resulting diseased plant is an unsightly mix of health green and infected dead reddish brown foliage. Older branches (more than one third inch in diameter) are more resistant to infection, and lesions that form on this size stem usually heal.
Phomopsis blight occurs anytime succulent young foliage is available. Spores from the previous year’s infected twigs cause infections early in the year. These new infections cause subsequent infections throughout the growing season. Infections become more severe with long periods of wet and warm conditions.
Damage from drought may be confused with Phomopsis blight. In both cases, tips of branches may be killed. However, the line between green and dead tissues is sharp in seedlings with Phomopsis blight and gradual in seedlings affected by drought.
What you can do
Susceptibility to Phomopsis blight varies considerably among junipers. Ask for resistant stock at your garden or landscape center or consider planting another type of evergreen.
Avoid planting junipers or other susceptible species in poorly drained areas.
Avoid wounding or injuring when planting or cultivating.
Prune out and burn or bury all blighted plant parts as they appear. The plant’s appearance will suffer greatly. This will reduce the severity of Phomopsis but will not eliminate the disease.
Restrict pruning and shearing to dry weather. Aggressive maintenance pruning will promote the growth of new, susceptible tissue, so wait for mid-summer dry conditions. Sterilize pruning tools between cuts and especially between plants, using rubbing alcohol or a 25 percent solution of chlorine bleach.
Do not use infected branches or needles as mulch.
If overhead sprinkling is used, water early in the day so the seedling dries before nightfall.
Remove a severely infected plant and replace it with one that is more resistant. Some juniper cultivars are less susceptible to the disease. You may also want to consider a different species.
The following juniper varieties are generally resistant to Phomopsis blight.
Juniperus chinensis – Chinese Juniper
- ‘Mint Julep™’
- ‘Pfitzeriana Aurea’
- ‘Robusta Green’
- var. sargentii (Sargent Juniper)
- var. sargentii ‘Glauca’
J. communis – Common Juniper
J. horizontalis – Creeping Juniper
- ‘Depressa Aurea’
- ‘Wiltoni’ (‘Blue Rug’)
J. sabina – Savin Juniper
- ‘Knap Hill’
J. Scopulorum ‘Silver King’
J. squamata – Singleseed Juniper
- var. fargesii
J. virginiana – Eastern Red Cedar
Phomopsis blight of junipers. U.S. Department of Agriculture Forest Service.
Focus on Plant Problems: Phomopsis Blight. University of Illinois Extension.
Juniper Twig Blights – Phomopsis and Kabatina – Shrubs. University of Maryland Extension.
Juniper Diseases & Insect Pests. Clemson Cooperative Extension.
Phomopsis Blight of Juniper. Missouri Botanical Garden.
Juniper Tip Blight. Adam Blalock and Dr. Fulya Baysal-Gurel. Tennessee State University.
Diseases of Trees and Shrubs. Sinclair, W.A., Lyon, H.H., and Johnson, W.T. Cornell University Press. Ithaca, New York. 1993.
Landscape Plant Problems: A Pictorial Diagnostic Manual. Byther, R.S., Foss, C.R., Antonelli, A.L., Maleike, R.R., and
Bobbitt, V.M. Washington State University Cooperative