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Gardening in Gwinnett: Several diseases can cause dead branches on Leyland cypress

The fast-growing Leyland cypress is very popular as a hedge because it can grow two to three feet a year in height. The trees can be a great addition to the landscape if they're properly planted and maintained.

But this tree is rapidly becoming one of the most troublesome in the landscape. Because of improper planting and overuse, Leyland cypress may go the way of the Red Tip Photinia, a popular hedge tree in the '80s that succumbed to a fungal leaf spot disease.

A Leyland cypress can grow to be 20 to 30 feet wide and at least 50 feet tall, forming a thick wall of limbs and needles. However, it is susceptible to attack from several diseases. In recent weeks, the extension office has received many calls from residents about dead branches in their Leyland cypress trees. That is not surprising, as the problem afflicting the trees is visible everywhere.

Because Leyland cypress has a relatively shallow root system and the plants are often planted too close together, they are prone to root rot and several damaging canker diseases, especially during periods of prolonged drought. The two most common fungal diseases are Seiridium canker and Botryosphaeria canker, also known as Bot canker.

Seiridium canker is probably the most prevalent disease on Leyland cypress in the landscape. The primary symptom is yellowing or browning of the foliage on the top or the lateral branches. The branches then turn bright reddish brown, in striking contrast to the dark, green healthy foliage.

Seiridium cankers ooze sap profusely, with a rather shallow canker forming dark brown to purplish patches on the bark. The disease is more apparent during droughts, and the cankers enlarge up to three times faster on drought-stressed trees.

A contributing factor to the diseases on Leyland cypress is that the trees are often planted too close together. They can grow 4 feet per year in height and 2 to 3 feet in width every year. The trees should be planted at least 10 feet apart - preferably 12 to 15 feet apart - and a minimum of 15 feet away from structures.

Leyland cypress trees require full sun all day. Shade will reduce their vigor, causing them to thin out and be more susceptible to diseases. They also need plenty of air circulation inside the canopy to dry out the leaves.

The trees should be planted in fertile, well-drained soils, because Leyland cypress cannot tolerate soggy soil.

No cultivars of Leyland cypress trees are resistant to Seridium canker, and no chemical fungicides can control the disease. The best way to deal with an infected tree is to prune out the dead branches. Cut below where the canker has formed on the branch, and sterilize the pruning tool in alcohol, bleach or hydrogen peroxide before making the next cut to prevent the spread of the disease.

Trees that have been extensively damaged or trees with infected trunks should be removed, because they cannot be saved. Remove dead limbs and other plant debris from beneath the tree to prevent rainwater from splashing the spores back up onto the tree.

For more information on Leyland cypress diseases, refer to the extension's publication "Diseases of Leyland Cypress in the Landscape" at http://pubs.caes.uga.edu/caespubs/pubcd/B1229.htm

Timothy Daly is an agriculture and natural resources agent with the Gwinnett County Extension Service. He can be reached at 678-377-4010 or timothy.daly@gwinnettcounty.com.