The dawn redwood (Metasequoia glyptostroboides) is a truly magnificent tree, native to central and western China, and is believed to have existed on earth for at least 50 million years. An imposing landscape tree, the dawn redwood can grow up to 100 feet tall. It seems a great shame that such a powerful tree can be damaged by spruce spider mites, tiny crawling insects that feed on foliage. You can help protect your dawn redwood by monitoring pest infestations and providing proper care.
Early symptoms of spruce spider mites include mottling or stippling patterns on older needles. The needles eventually turn yellow or bronze, dropping prematurely. If populations are allowed to remain and grow, twigs and branches may die. Particularly in the case of a young, stressed tree, a dawn redwood may be killed in severe cases. Though spider mites are often associated with hot summer weather, spruce spider mites are most active in cool spring and fall weather.
To assess the proper course of action, it's important to monitor the tree to see how severe the infestation is. Tap a branch over a piece of white paper to check for mites. Beneficial mites are reddish and faster-moving than spruce mites, which are green or brown. When crushed, beneficial mites stain red and spruce mites stain green. If beneficial mites outnumber spruce mites, you don't need to do anything. The beneficial mites will prey on the spruce mites and keep the population low.
Spraying branches with a direct stream of water once or twice a week may help dislodge colonies of mites. If your dawn redwood is small, applying neem oil on the branches and needles late in the growing season can help smoother eggs that will otherwise hatch in spring. Neem oil must be diluted with water, usually 2 tablespoons of oil per 1 gallon of water unless otherwise stated on the label. Follow all warnings from the product label and wear protective eyewear, long sleeves and long pants when using neem oil. Keep children out of the area when you're spraying neem oil.
A healthy dawn redwood is less likely to develop a pest infestation. This is especially true when it comes to moisture, as mite infestations are worse on drought-stressed trees. Grow your dawn redwood in consistently moist soil -- a humus-rich, slightly acidic and well-draining soil is best. Grow the tree only in U.S. Department of Agriculture plant hardiness zones 4 to 8, in full sun and with plenty of space to spread its roots and branches.