The Italian cypress is very drought tolerant after it becomes established in the landscape. Mature trees benefit from occasional deep irrigation. Older trees planted in good soil can survive with little or no supplemental irrigation if winter rainfall is adequate.
A few insect pests and diseases can damage Italian cypress. Most serious is a fungal disease, cypress canker. Leyland cypress is especially susceptible to the disease, and it should not be planted in San Diego county. The disease also attacks Italian and Monterey cypress especially when they are planted in inland areas.
Cypress canker can infect susceptible plants through airborne spores when foliage is wet from rain or dew. Splashing water can also spread the disease within the plant’s canopy. Resinous lesions (cankers) which form on infected bark gradually enlarge and girdle twigs and branches. Infected branches and the tops of trees turn yellow or brown and die. The disease often progresses until the tree is killed.
There is no effective chemical treatment for Cypress canker. Pruning out the diseased parts of the tree may prolong its life if this is done when symptoms are first observed. Make pruning cuts in healthy wood well below any apparent cankers. When the top of a tree is infected, you may have to remove the top several feet below the damaged area. Pruning is of little value when the lower portion of the main trunk is infected.
Additional information on Cypress canker can be found in UCANR publication 3359, Pests of Landscape Trees and Shrubs,
By V. Lazaneo, Urban Horticulture Advisor, Emeritus, UC Cooperative Extension August 2012