Question
We have 12 cypress trees surrounding our yard in Maryland.  They are about 15 years old.  Two summers ago one tree developed brown branches; each summer now the brown patches seem to have spread to the other trees.  Can we save them before it's too late!

Answer
Several diseases are becoming more common on cypress. These include Seiridium and Botryosphaeria cankers, Cercospora needle blight, If I had to guess i would think it was Seiridium canker. Even though there is not a fungicide recommended for this disease you may want to check with your local nursery and they should be able to recommend a fungicide that is used locally to treat this disease. One fungicide I have heard may help is thiophanate-methyl fungicide  applied as a full-coverage spray at monthly intervals from April to October. Ask your nurseryman.

Seiridium canker, caused by Seiridium unicorne, is probably the most damaging disease on Leyland cypress. Plants of all sizes and ages are affected. Cankers may form on stems, branches and in branch axils causing twig, branch or, at least on smaller plants, stem dieback. Cankers appear as sunken, dark brown or purplish patches on the bark, often accompanied by extensive resin flow. It should be noted that resin exudation often occurs from the branches and stems of otherwise healthy plants of Leyland cypress thus resin flow by itself is not a diagnostic characteristic for Seiridium canker. Scattered twigs or branches killed by the fungus turn bright reddish brown, and are in striking contrast to the dark green healthy foliage. Fruiting bodies of the fungus appear on the bark surface of the cankers as small circular black dots barely visible to the naked eye. Spores of the fungus are spread to other parts of an infected tree, or from tree to tree by water splash from rain or irrigation. The fungus also can be spread from tree to tree on pruning tools. Long distance spread appears to be through the transport of infected cuttings or plants.

Currently there are no chemical control measures recommended for the disease in the landscape or nursery. Avoiding water stress and tree wounding may reduce infection. Infected branches or twigs should be pruned and destroyed as soon as symptoms are noted. Prune at least one inch below the canker, and sterilize the pruning tools between cuts by dipping them in rubbing alcohol or in a solution of 1 part chlorine bleach to 9 parts water. Tools should be cleaned and oiled after using bleach to prevent rusting. Severely affected plants should be removed and destroyed.

Botryosphaeria Canker

The outward symptoms of Botryosphaeria canker, caused by Botryosphaeria dothidea, are similar to those of Seiridium canker; that is, scattered bright reddish-brown dead twigs and branches occurring in otherwise healthy foliage. Cankers on small twigs and branches are also similar to those caused by S. unicorne, except that extensive resin exudation usually does not occur. Unlike S. unicorne, however, B. dothidea may produce long, narrow cankers on the trunk that might extend for a foot or more in length. These cankers rarely girdle the trunk, but will kill any branches that may be encompassed by the canker as it enlarges. Fruiting bodies of the fungus, perithecia and/or pycnidia, are produced just beneath the bark, but their presence can be discerned as tiny raised pimples scattered over the surface of the canker. Spread of the fungus is similar to that described above for S. unicorne, except that ascospores of B. dothidea may be spread by wind.

Botryosphaeria canker most often occurs on plants that are under considerable stress, and an effective control strategy should include keeping the plants growing as vigorously as possible. Mulch plants yearly and provide adequate water during extended dry periods. Avoid heavy fertilization and severe pruning of established plants. Prune out and destroy dead branches. Effective chemical control is not available.

Cercospora Needle Blight


Cercospora needle blight, caused by the fungus Cercosporidium sequoiae (syn. Asperisporium sequoiae; Cercospora sequoiae), is a relatively new disease on Leyland cypress. However, it a common disease on species of Juniperus, Thuja, Cupressus, Taxodium, Cryptomeria, Sequoia and other genera. The first symptom of Cercospora needle blight is a browning of the needles in the lower crown next to the stem. The disease slowly spreads upward and outward until, in severe cases, only the needles at the tips of the upper branches remain green. In a general way, these symptoms mimic those caused by severe stress where the interior needles turn yellow and fall off. Fruiting bodies of the fungus appear as tiny, greenish pustules on the upper surface of the needles or on small twigs. Spores (conidia) are present throughout the spring and summer and are spread by wind. Infection usually occurs during periods of wet weather.

Cercospora needle blight can be controlled by spraying with copper-containing fungicides. There are no fungicides registered specifically for the disease on Leyland cypress, but Kocide is registered for general use on ornamentals. Spray plants at 10-day intervals from bud break until new growth matures.