Dec 2022
- My well-established juniper has noticeable dieback. The damage is random. Some tips are brown. Some areas in the centre are dead. What can be causing this problem and what can be done about it?
Juniper dieback can be caused by biotic or abiotic factors. There may be a magnesium deficiency in the soil, as foliage becomes yellow (chlorotic) or dies toward the center of the plant. A soil test can determine if this is the case, and it can be amended.
Junipers are generally susceptible to blights (dieback of stem tips), particularly in very rainy springs. Juniper twig blight is caused by the fungus Phomopsis juniperovora and can turn leaves yellow and eventually whole branches. Look closely at the plant. If there appears to be a fungus, prune out and destroy infected branches during a period of dry weather and sterilize equipment between cuts. Good air circulation and reducing crowding will help encourage faster drying of foliage and reduce the chance of an infection spreading. Avoid watering from above, and in the evenings.
Another note is that the mature evergreen shrubs do not develop new growth on old wood, so the centres on old plants can develop bare zones. As well, soil that is heavy clay or waterlogged can cause plants to do poorly. Too much mulch that is holding in moisture or landscaping fabric can also cause problems with waterlogged roots and spore fungi. Ice coatings on the shrubs for more than a few days can also cause damage to the leaves.
Sources:
https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=r540
https://extension.wsu.edu/snohomish/juniper-troubles/
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