“One of the easiest and best ways to tell the difference between Seiridium and Bot canker is to run your hands across the branches of newly affected trees. If the needles fall off upon touching, then it is Seiridium and if they stay attached then it is Botryosphaeria. Using this method, you will probably be right almost 100 percent of the time. What I found to be the best control for both cankers, but especially Seiridium canker, is irrigating trees during periods of drought or low rainfall.”
Of course, the follow-up question to “What is killing my Leyland plants?” is “What can I do to stop this?” As Dr. Woodward mentioned, proper irrigation during hot, dry periods is essential in helping to prevent these diseases, but what about after the disease is already present?
On trees already infected, the best control is to prune the brown (dead) branches from the tree. This will make the tree look better and it will also reduce disease spread by reducing the fungal inoculum. Make certain that you disinfect your pruning tool between each and every cut. This is the best way to be sure you’re not further spreading the fungus. For small pruners, dip the cutting blades into a weak bleach solution (1 part bleach to 9 parts water). For larger tools, you can spray the blades with the same solution, using a clean spray bottle. Remember to disinfect between each cut. Once this is done, then irrigation is the best remedy to prevent any smaller cankers from expanding to kill more of the plant. The one thing that needs to be stressed for Leylands showing brown or dead branches now is that the original infection probably occurred years ago, and that the symptoms are only now becoming evident as the cankers have enlarged. Therefore, fungicides are not that effective in controlling the diseases at this time. There also is no good data that indicates that any fungicide is effective in controlling Seiridium or Bot cankers. Even if chemicals were available, spraying a Leyland to control the canker diseases is not easy, as there is usually no way to spray the entire tree at very regular intervals (every seven days) throughout the year. Important keys in preventing Leyland diseases are:
* Not to injure trees when planting or working around them;
* Not stressing Leyland’s by planting them too close together; and
* Irrigating Leyland’s during periods of drought or in summer when rains cannot be counted on.
If your Leyands are severely affected, the best control is to remove the damaged trees and replant with something else or even more Leylands if that is what is wanted. Within a few years, the new trees will grow so fast that the loss will hardly be noticed.
Other trees are available that do not have as many disease problems as the Leylands. A suitable and similar replacement would be to choose an arborvitae. Another good choice would be a holly, although they are much slower growing. Call the Cooperative Extension office if you have questions about any of the trees or shrubs in your yard or if you are I need of a recommendation.
Information about Extension Solutions for Homes and Gardens can be found on the University of Georgia Cooperative Extension website at www.caes.uga.edu/extension/cherokee or by contacting the Cherokee County Extension Office at 100 North St., Suite G21 in Canton at (770) 479-0418. The Georgia Extension Master Gardener Program is a volunteer training program offered through county offices of the University of Georgia Cooperative Extension.