Leyland Cypress Dieback
By Roosevelt McWilliams County Extension Agent

Home & Garden Tips

About this time of the year, I always receive dozens of calls concerning Leyland Cypress trees. The most frequently asked question

is why are the branches on my Leylands t u r n i n g brown and dying? The reason that

limbs are

browning and dying right now is largely due to two disease problems which are Seiridium Blight and Botryophaeria Canker. Both of these diseases are caused by fungus.

Keep in mind that we are talking about dieback that is occur- ring now, during the spring. Later this summer, hot weather and drought will also become a factor. I have noticed a large number of Leylands in the County myself with brown or yellowishbrown limbs. I contacted Dr. Jean Woodward, a plant pathologist with the University of Georgia Extension Service in Athens and asked her which disease was presently causing the problem and how to tell the difference.

The following was her reply:

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 ice 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 appearing yellow, some light tan, some brown.

All Seiridium Cankers ooze sap profusely, but the canker is rather shallow, as opposed to Bot Canker which infects the rays of the wood causing a deep canker, often in a V-shape when the branch is transversely cut. If cutting a Seiridium Canker with a knife, cut at the oozing site, but cut shallowly, and beneath the bark layer. The tissue underneath is usually bright red and sticky because of the sap.

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. 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 no longer visible, and trees are healthy today (4 to 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 disappointment. In greenhouse, tests were found that Seiridium Cankers expanded three times faster on drought stressed trees than on non drought stressed trees. The same effect with Botryosphaeria Cankers were not seen.