Leyland cypress, an evergreen tree, has become a popular choice for residential and commercial landscapes. This tree can be used to create screens or hedges, and is generally very healthy and trouble-free. On occasion, however, the Leyland cypress can become threatened by a few different diseases.
The most serious disease to infect the Leyland cypress tree is Seiridium canker. As this disease infects the cypress, the leaves become discoloured and turn brown in colour. The bark and branches of the tree develop sunken cankers that are dark brown or purple in colour and that secrete resin. As this disease progresses, twigs and branches will die, becoming reddish-brown in colour. This fungal disease is spread through spores, which can be transported by wind or water in the form of irrigation.
Any branches or twigs that have become damaged should be pruned from the plant. After each cut, shears should be sterilised to prevent the spread of the spores to other branches or other trees. Unfortunately, no available chemical control methods available have proven effective in treating this disease.
Cercospora Needle Blight
Needle blight is a fungal disease caused by Cercosporidium sequoiae. Symptoms of needle blight include the browning of Leyland cypress needles. This occurs in the lower crown, near the stem and slowly spreads upwards as the disease progresses. The fungus that causes this disease also produces pustules that are green in colour and are visible on the upper surface of the needles. Disease needles will fall from the tree.
Fortunately, Cercospora needle blight can effectively be controlled with the application of copper fungicides, which are available at local garden centres. All fungicides should be applied per manufacturer instructions. For this disease, it is recommended that the fungicide be reapplied in 10-day intervals.
Phytophthora Root Rot
Phytophthora root rot is a common disease among many species, including the Leyland cypress tree. The smaller shooter roots or newly established roots are the most susceptible to becoming damaged by this disease. As this disease infects the root, they become brittle and discoloured, inhibiting their ability to absorb necessary nutrients from the soil. As the roots become damaged, the needles of the Leyland cypress tree will yellow and die back. In severe cases, this disease can kill the tree.
The best method of control is to prevent root rot by providing an ideal growing environment. The fungi which cause these diseases grow rapidly in wet, warm conditions. Protect the tree by keeping the soil from becoming overly saturated with water during the spring and summer months. In a nursery setting, the application of Subdue Maxx has proven effective.
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