tools when you are pruning affected branches with a 10 % bleach solution . If trees become too crowded you also may consider removing some to increase air flow between them .
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 % of the time . The reason is that Botryosphaeria cankers expand to girdle the branch , which when it gets large enough , kills the branch fairly quickly . Hence the needles remain attached . However for Seiridium canker , the cankers don ’ t enlarge to girdle the branch . Rather , the cankers enlarge longitudinally , with multiple cankers developing around the branch . Collectively , the cankers interfere with water flow and the branch wilts , yellows , and eventually turns brown . Because of the lack of water , the symptoms often resemble drought stress , and the needles will fall off when touched . Also , Bot canker tends to affect one or two branches in a localized area , such as at the base of the tree or where the tree was pruned or injured from storms , etc . Seiridium canker is often the result of drought stress or some other kind of stress that weakens the tree . Infection requires a wound , but it appears to also enter through lenticels , although I was never able to conduct an experiment to prove it . As a result of this infection , Seiridium cankers often appear randomly distributed across the tree canopy , with some appearing yellow , some light tan , some brown .
What I found to be the best control for both cankers , but especially Seiridium canker , is drip irrigating trees during periods of drought or low rainfall . However , please do not over do it !! In field inoculated trees , Seiridium cankers developed after inoculating . However , under irrigation the trees were able to heal around the canker site so that within 1-2 years the canker was not longer visible , and trees are healthy today ( 4-5 years after inoculating ). Although I was glad to know the effect of irrigation , the study was actually set up to evaluate canker development over time - so healthy trees were a disappointed ! In greenhouse tests we found that Seiridium cankers expanded three times faster on drought stressed trees than on non-drought stressed trees . I did not see the same effect with Botryosphaeria cankers .
Of course , the follow up question to “ What is killing my Leylands ” is - “ What can I do to stop this ?” As Dr . Woodward mentioned above , 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 . 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 . Spraying a Leyland to control the canker diseases is not easy anyway , as there is usually no way to spray the entire tree at very regular intervals ( every 7 days ) throughout the year . Important keys in preventing Leyland diseases are 1 ) not to injure trees when planting or working around them ; 2 ) not stressing Leyland ’ s by planting them too close together ; and 3 ) irrigating Leylands during periods of drought or in summer when rains cannot be counted on . If your Leylands are severely affected , the best control is to remove the damaged trees and replant with something else . I would suggest replacing poor looking Leylands with hollys , wax myrtles , or tea olives . These alternatives will look better and have a longer lifespan as well .
If you have questions about Leyland cypress disease or other tree related subjects contact the Thomas County Extension Office .
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