Leyland cypress has been widely touted in recent years as the fast growing, pest-free, do-it-all tree for southern landscapes. It has gotten a reputation as a low maintenance tree but leyland cypress is not. When managed properly, leyland cypress does mature into an attractive tree. The problem is that this tree has often been over-planted on sites where it's not well adapted or maintained. Such trees, when exposed to prolonged drought or extreme cold, are predisposed to attack by stress-induced plant diseases. The net result is that leyland cypress in landscapes across the South are dropping like flies.
Seridium canker was first described on the Monterey cypress in California in the mid-20's. By the 40's, stands of this tree, which is adapted to a maritime climate, were wiped out on dry and hot inland sites by a canker disease caused by Seridium cardinale. By the mid-80's, this same disease was found in California on leyland cypress. Within the past five years, this disease has been reported across the Southeast on this same tree. Two other members of the genus Seridium, S. unicorne and S. cupressi, also cause canker and dieback diseases in juniper and cypress.
A fading or yellowing of the foliage on a few twigs to the entire tree is the noticeable symptom of Seridium canker. Death of the leading and lateral shoots is caused by the formation of girdling cankers on the twigs, branches, and trunk of the trees. The fungus often invades the tree through wounds on the twigs or branch bases. Lens-shaped cankers on the branches may appear as gray discolored areas on the bark. Resin often oozes from the cracks in the bark on the surface of the canker. Fruiting bodies of the causal fungus appear on the bark as small black dots about the diameter of pencil lead. Spores of the causal fungus are spread to healthy foliage by splashing water and pruning tools. The disease is readily dispersed to new loations on diseased liners, cuttings, and container material. Insects may also be involved in pathogen dispersal.
Sanitation practices are often the best defense against Seridium canker. In a container nursery, cuttings must not be taken from diseased leyland cypress. In addition, all diseased liners, container, and field stock should be immediately destroyed. In landscapes, prune out branch and twig cankers. If the main trunk is damaged, remove the tree. Also, all containers, pruning tools, and other equipment should be cleaned prior to each production cycle. Prior to each cut, pruning knives should be dipped in alcohol or a germicidal soup.
Proper establishment and management practices should minimize the impact of moisture and/or temperature-related stress on tree vigor. Closely-spaced screens and hedges of leyland cypress should be avoided. Leyland cypress mature into big trees and they should be spaced accordingly in the landscape. During prolonged drought, thorougly soak the soil about every 5 to 7 days around the base of leyland cypress.
No fungicides are currently cleared for the control of Seridium canker on leyland cypress.
A second canker disease of leyland cypress, called bot canker, has recently emerged in landscapes across the South. Bot canker may be a more common and destructive disease of leyland cypress than Seridium canker. The causal fungus, Botryosphaeria dothidea, is well known as a pathogen of a wide variety of shrubs and trees that have been weakened by drought. Development of this canker and dieback disease on leyland cypress may be related to drought or transplant shock.
Symptoms are similar to those of Seridium canker. Yellowing or browning of the foliage on a shoot or branch are usually the first symptoms seen. An elongated, slightly sunken canker can be found at the base of the dead shoot or branch. The canker surface may be cracked and darker than the surrounding healthy bark. Apparently, there is little or no resin flow from these cankers.
Control measures are similar to those described for Seridium canker. Prune out diseased branches below the dead wood. To minimize stress, follow proper establishment procedures, space out plants, mulch with pine bark or pine straw, and irrigate during lengthy periods of hot and dry weather. Avoid heavy fertiliztion, particularly in late winter and the fall. Fungicides have been shown to be ineffective against bot canker.
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