Cankers may be visible at or below the soil line. There is no practical chemical control for home gardeners. Do not plant Leyland cypress where Phytophthora is known to be present. Improve soil drainage by adding organic material to heavy, clay soils and avoid overwatering. This disease is caused by the fungus Botryosphaeria species.
Symptoms are dieback of a leader or major side branch.
Beneath the bark there is dark brown discoloration with a definite margin between diseased and healthy tissue. Reduce the stress on the plant. Prune back diseased branches or stems below evidence of dead wood. Mulch plants properly and provide adequate water during dry periods. Pruning wounds may be sprayed with a thiophanate-methyl fungicide.