Leyland cypress is a fast growing landscape tree that thrives in Northern temperate climates. This pyramid-shaped tree grows quickly--as much as up to 3 feet every year--and is popular during Christmas. Like most trees and plants, it too is prone to a number of diseases that adversely affect its health and even cause it to die in extreme conditions.
Annosus Root Rot
A fungus called Heterobasidion annosum causes this root disease in Leyland cypress trees. Initial infection spreads through spores on stumps of freshly cut conifer trees. It then spreads through the stump and reaches the roots, and can infect adjacent trees as well through root contact. Symptoms include yellowing and decline of the infected cypress followed by sudden death, or the sudden change in foliage color from green to brown.
Phytophthora Root Rot
This disease is caused by the Phytophthora cinnamomi fungus that affects smaller roots on young Leyland cypress trees instead of established ones. This disease is a problem in the nursery and landscape and occurs where soil drainage is poor. Foliage of infected plants turns yellow and experiences tip die-back. Only lab analysis on samples of infected roots can confirm the presence of the fungus.
Cercospora Needle Blight
Caused by the Cercosporidium sequoiae or Cercospora sequoiae fungus, this disease is relatively new on Leyland cypress trees. Initial symptoms include browning of the needles next to the stem. If left untreated, the disease spreads upward until all the needles turn brown except those located on the highest branches.
Seiridium canker is caused by Seiridium unicorne. North Carolina State University's Plant Pathology Extension states that this disease is probably the most damaging Leyland cypress disease because it affects plants of all ages and sizes. Cankers form on stems, twigs or branches of infected trees, causing stems to die back. A canker resembles a sunken purple or deep brown patch on the bark that emits a resin. Infected parts of the tree turn deep brownish-red, a striking contrast against the green foliage. The fungus spreads through spores from one part of the same tree to another, or to a different tree through splashing of rain or irrigated water, or contact with infected pruning equipment.
Caused by Botryosphaeria dothidea or Bot, the outward or physical symptoms of this canker are similar to those of seiridium canker. Even cankers appear the same, except the ones caused by this disease do not emit heavy resin flow. If the needles fall off after you run your hand over the infected areas, the disease is caused by Seiridium unicorne. Botryosphaeria Canker appears on severely stressed Leyland cypress trees. Keep your Leyland cypress trees well watered during hot summer days and periods of drought.