What Is Making the Aptos Blue Evergreen Trees Turn Brown?
"Aptos Blue" is a popular cultivar of the coast redwood, the tallest known tree in the world. The "Aptos Blue," known for its blue-green foliage and dense growth, can grow to a height of around 350 feet. Redwood trees have a 600-year average lifespan, but they face several problems that can cause them to turn brown and die. Does this Spark an idea?
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Salt
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Coast redwood trees are sensitive to salt, although some varieties are more sensitive than others. Among the more sensitive cultivars is "Aptos Blue." Ocean breezes carry sea salts that can kill redwood foliage and seedlings by dehydrating them. Symptoms include yellowing and browning of needles. In addition, many communities in California use recycled water, which can also contain high levels of sodium. Coast redwoods shouldn't be planted near the seacoast and their soil should be monitored for salt levels. Soil salinity for "Aptos Blue" should be less than 2 decisiemens per meter.
Botrytis
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Botrytis canker attacks trees that seem to be healthy. Symptoms include wilting and browning of branches along with dieback. Removing the bark will reveal reddish-brown discoloration. Bark over cankered areas may peel off, or the cankers may be surrounded by callused wood. Fungicides are ineffective against this disease. Control botrytis by pruning dead wood and disinfecting pruning tools between cuts. Trees that have been wounded by pruning are particularly susceptible to botrytis.
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Armillaria
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Armillaria root rot occasionally attacks coast redwoods that are stressed from over-watering or drought. Symptoms include the appearance of yellowish-brown colored mushrooms growing at the base of the tree, and white fungal threads growing under the bark. Additional symptoms include yellowing or browning of needles and twig or branch dieback. As the disease progresses, the wood becomes light yellow or white and stringy. Control armillaria by removing severely infected trees, including the stumps and large roots and burning them. Trees that aren't too severely infected can be saved for a awhile by removing the soil around the root collar and letting it dry during the growing season. Remove infected bark and wood on the roots and trunk by cutting back to healthy tissue.
Ramorum Blight
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Ramorum blight and dieback, or sudden oak death, is caused by the phytophthora ramorum organism, which attacks redwoods as well as oaks. Needles of infected trees turn brown and trees suffer from tip dieback. Because other trees have more serious symptoms, quarantines are in place in California and in Oregon to keep this disease from spreading. Ramorum blight spreads through air currents, on muddy shoes and tires and by spores found in plant material. Contact your local county extension for more information on the best ways to manage this disease.
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References
- University of California; Coast Redwoods as Landscape Trees; Michelle La Strange; April 2010
- Urban Forests Ecosystems Institute; What's Up With The Redwoods; James Downer; September 2004
- Virginia Cooperative Extension; Botryosphaeria Canker and Dieback...; Elizabeth A. Bush
- Integrated Pest Management: RPD No. 602 - Armillaria Root Rot of Trees & Shrubs
- Oregon State University Phytophthora Online Course: Symptoms and Identification on Other Hosts
- University of California; Landscape Plant Selection Guide for Recycled Water Irrigation; Lin Wu, et. al.
Resources
- Photo Credit Ryan McVay/Lifesize/Getty Images
