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  • Writer's pictureDrix


We have been seeing a lot of brown foliage in incense cedars, Leland cypress, Italian cypress, arborvitae and other host-specific evergreen trees and shrubs all over our Clark County area. Some of this is normal flagging, caused by the hot, dry summer weather we experienced this year. Generally, the entire tree has a somewhat uniform distribution of brown foliage throughout. This is an environmental condition, and not damaging to the trees.

However, an alarmingly growing number of trees, especially incense cedar, are developing brown foliage that is not uniformly distributed, but usually starts at the bottom of the tree and seemingly randomly spreads around the tree. This is seiridium canker (pathogen: seiridium unicorne). This is a fairly new disease in our area, but it is spreading rapidly.

Seiridium often begins with only one or two branches becoming infected and turning brown. A small depression forms on an individual limb, which may or may not weep pitch and gradually develops into a noticeable canker. The fungus survives in the infected bark tissue and forms spores. In wet weather the spores are released and infect other branches and can move into susceptible, near-by trees and shrubs.

Controlling this disease is very difficult. First and foremost, it has to be diagnosed, the earlier the better. If the infection is found to be new and contained to only a few branches, it may be possible to save the tree with immediate pruning and possibly some copper fungicide applications, which are not curative, but may aid in keeping the pathogen from spreading.

If the disease has spread beyond the point where pruning is aesthetically practical, the tree or shrub should be removed and the debris destroyed, preferably by burning.

The first photo is of a large, heavily infected incense cedar. Second photo is a large, very well established seiridium canker.

This is not a problem the average homeowner is equipped to deal with. Pruning out infected branches must be done properly to avoid spreading the disease, and disposal of debris is equally critical to minimize the chance of spreading the disease to other, susceptible plant materials. In short, this is definitely a problem best addressed by licensed, experienced landscape professionals. So give us a call or send an email, we will come out and give you a definitive diagnosis and recommendation or estimate for dealing with the problem.

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