Table of Contents
Tip dieback in junipers has been a concern in the nursery and landscape. Dieback may result from biotic factors such as insects or diseases, or from abiotic factors such as physiological problems and stresses. Two fungi, Phomopsis juniperovira and Kabatina juniperi can cause die back in many different juniper species. In order to properly manage these diseases, correct identification is necessary.
- Host range:
- Abies spp., fir;
- Chamaecyparis spp., false cypress;
- Cupressus, spp., cypress;
- Juniperus spp., junipers;
- Larix spp., larch;
- Metasequoia spp., redwood;
- Taxus spp., yew;
- Thuja spp.,white cedar; and
- Tsuga spp., hemlock.
- Life cycle: Fruiting bodies, called pycnidia develop
in the grey canker which develops at the base of previously killed
shoots and twigs. These appear about three to four weeks after
infection. Pycnidia are embedded within the plant's tissue, however,
during wet weather, pale green to cream coloured masses of conidia,
or spores, exude. These are dispersed by wind and water to infect
new tissues. Spores, are released continuously through out the
growing season, infect when environmental conditions are optimum.
Fall infection is more frequent.
Newly developing tissues are very susceptible to the fungus. Infection may occur late in the season, if growth is prolonged and encouraged by heavy pruning, high fertility and excessive moisture. An infection may begin within seven hours on a wet surface when temperatures are 20-24 °C. Prolonged wet periods promote and enhance the severity of the disease. Following infections, high temperatures intensify the severity of symptoms.
- Symptoms: New growth and immature scale leaves and needles
are the most susceptible to infection. Mature leaves appear to
be more resistant. The disease begins as small lesions first appearing
as tiny yellowish spots. As the fungus advances in to the water
conducting tissues, diseased shoots fade becoming light green
and eventually turning reddish brown. A greyish band or canker
can be noted at the base of infected shoots. Diseased shoots remain
on the plant for sometime eventually turning grey.
This discoloration occurs later during the growing season. Twigs less than 1 cm in diameter may be girdled.
Twigs 5 years old and younger may be affected by Phomopsis.
- Host Range: Many of the same,
- Cupressus spp.; Cypress;
- Junipers spp., Junipers and
- Thuja, white cedar.
Many of the same plants as attacked by P. juniperovora.
- Life Cycle: The life cycle of Kabatina juniperi is similar to that of Phomopsis juniperovora. Kabatina does not penetrate healthy tissue but enters through wounds caused either by insect or other injuries. Spores, frequently released in the fall, are spread by water. Greatest infection occurs when temperatures are 16 to 21 °C.
- Symptoms: Twigs from the previous growing season which have been infected by Kabatina show symptoms the following spring as foliage begins to lose its winter colour and new growth begins. Affected tips turn yellow and eventually brown instead of green. As with Phomopsis, greyish lesions develop at the base of blighted twigs.
In order to determine which fungus is causing the twig die back, samples must be cultured and spores examined. A relatively easy field diagnostic tool is to carefully shave off the outer bark. If the tissues show an even gradient of brown to green tissue, then desiccation is probably the cause of the dieback. A very distinct border or margin between dead and healthy tissues indicates a die back caused by a canker. This does not confirm either of the dieback fungi, rather it indicates the original injury may or may not be disease related.
These diseases are primarily a problem in seedling, nursery stock and in the landscape. Control measures should consist of both chemical and cultural control practices.
Some species and cultivars are reportedly resistant to Phomopsis:,
- Juniperus chinensis
- cv. 'Foemina
- CV 'Procumbens'
- CV 'Iowa'
- CV 'Keteleeri'
- CV 'Pfitzeriana Aurea'
- cv.'Knap Hill'
- CV 'Robusta'
- var. sargentii
- var. sargentii
- CV 'Glauca'
- cv.'Silver King'
- CV 'Shoosmith'
- cv.'Depressa Aurea'
- cv.'Prostrata Aurea'
Promote plant health by maintaining pH and soil fertility, reducing drought stress and relieving soil compaction. However, avoid creating situations which create excessive juvenile growth. It is more susceptible to Phomopsis.
Where possible, prune out and destroy infected branches during dry weather and sterilize equipment between cuts. Providing good air circulation and reducing crowding will help encourage rapid drying of foliage and reduce the chance of an infection starting.
Avoid overhead irrigation late in the day. Rogue and destroy any heavily infested plants. New growth must be protected during wet weather with fungicide applications to prevent infections.
No fungicide appears to give complete control. For chemical registrations, order OMAFRA Publication 840, Crop Protection Guide for Nursery and Landscape Plants.
For more information:
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