Tree Diseases: Phomopsis Blight of Juniper (Phomopsis juniperovora)
Phomopsis blight of juniper, also called twig blight of juniper, nursery blight, cedar blight, juniper blight, or needle blight is a significant fungal disease of eastern red cedar, and other junipers. It is caused by the pathogen Phomopsis juniperovora. The disease causes a progressive dieback of infected needles and stems. Severe infections can result in plants being partially to completely defoliated. Infected plants generally decline rapidly, and may expire.
Distribution & Habitat
Phomopsis blight of juniper occurs globally, wherever susceptible plants are present.
Phomopsis blight of juniper most commonly infects eastern red cedar, creeping juniper, Rocky Mountain juniper, and Savin juniper. Arbovitae, Chinese juniper, common juniper, cypress, Douglas-fir, English yew, European larch, false cedar, fir, jack pine, Japanese cedar, Japanese plum yew, true cedar, and white cedar may also be infected.
Phomopsis blight overwinters on previously infected needles and stems. In spring, during warm, wet conditions, fruiting bodies called pycnidia arise on the diseased plant tissue. The fruiting bodies produce asexual spores, or conidia, that are released into the air and dispersed by air currents, splashes of rain, or insect vectors to nearby plants, which they readily infect. The spores germinate in the youngest needles and stems. Germination is completed within seven hours. Older branches are generally more resistant to blight infections, but can still be affected.
The infected needles and stems are blighted, turning brown by mid-summer. Sunken cankers, or lesions, develop at the junction where the live and dead tissue merge. Within 3 to 4 weeks, more fruiting bodies develop on the diseased plant material, and the cycle begins anew. If conditions are favorable, infections may continue into late fall. Seedlings, young plants, and transplants are frequently infected in nurseries and gardens. Phomopsis infections are most widespread in spring and fall.
Symptoms of Infection
Yellow spots form at the tips of new needles. As the infection advances from the needles into the stems, it causes the new shoot tips to turn brown, and die back. The infection will then progress into the main stem, resulting in a progressive dieback of infected needles and branches. Infected needles will initially turn light green, before darkening to a reddish-brown, followed by an ashen grey. Lesions frequently develop on infected stems. Small stems are typically girdled by these cankers. When the fruiting bodies are mature, they can be observed as small, black spots on infected plant material. Defoliation generally occurs on the lower or central portions of infected plants. Severe infections may cause plants to be entirely defoliated. Plants that suffer from repeated blight infections may eventually fail.
- Promptly remove infected branches to prevent the spread of the disease.
- Cull dead or severely infected plants. Dispose of all diseased plant material. Avoid composting any infected plant debris.
- Numerous fungicides are registered for use in control of phomopsis blight. Applications should begin in early spring, as the pathogen becomes active. To effectively control the disease, applications should be performed at 10 to 14 day intervals, until mid-summer. Applications may resume in fall, if conditions are conducive to infection.
- When planting, select varieties that exhibit an increased resistance to blight infection.
- Use irrigation or soaker hoses to water plants. Try to keep foliage from being drenched with water.
- Prune vulnerable plants to improve air circulation, and promote a rapid drying of the foliage.
- Maintain plant vigor through sound cultural practices.
- Ensure that plants are sufficiently watered, especially during extended periods of drought.
- Apply a layer of organic mulch around the base of susceptible plants to improve the soil quality, and retain soil moisture.
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Photo courtesy of Melodie Putnam