Coastal Redwood Pests

Scale Insects

• Coastal redwoods occasionally attract armored scale pests, including redwood scales and black araucaria scales. These tiny pests typically get no larger than 1/8 inch in diameter and secrete plate-like coverings that protect their soft bodies. Crawlers emerge from the eggs and quickly find a good feeding spot. Once a crawler settles into a location, it molts, loses its legs and starts forming its armored covering. These unusual looking pests often look less like recognizable insects and more like small bumps growing on plant tissue.

  Scales pierce the bark or foliage with their straw-like mouthparts and suck out the cell contents. Although scales typically don't cause permanent damage to redwood trees, severe infestations may cause the needles to turn yellow, wilt and fall from the tree. Infested bark may split open and ooze a sticky substance.

Spider Mites

• Spruce spider mites are tiny arachnids that enjoy feeding on a coastal redwood's tender new foliage. Spider mites feed by piercing the foliage and withdrawing the fluids, which causes the needles to initially develop a speckled, stippled or yellow appearance. Prolonged feeding causes the needles to turn bronze or bleached of color before dropping from the tree. Spruce spider mites also produce a fine silk webbing that they spin around the twigs and needles.

Bark Beetles

• Redwood and cedar bark beetles occasionally attack weakened coastal redwood trees. These shiny, red-brown to black pests typically feed on the twigs to get up their strength for mating. The feeding activity may weaken the wood tissue, which causes it to break and dump small sections of foliage to the ground. After mating, the beetles tunnel beneath the bark where the females deposit their eggs. The tunneling activity causes small holes to show up in the bark and fine dust to appear at the base of the trunk or in the cracks of surrounding bark. Fortunately, the boring activity doesn't threaten the health of most coastal redwood trees.

Nonchemical Pest Treatments

• No chemical sprays are available that effectively treat bark beetles in home landscapes, as of June 2013, so prune out and discard all branches and foliage with heavy beetle populations. Pruning off infested plant tissue also helps control scale populations, as does gently scrubbing off the little pests with an old toothbrush.

  Spraying the foliage with a forceful stream of water from a garden hose twice a week helps reduce spruce spider mite populations. Be sure to spray the undersides of leaves where the mites tend to gather. Spider mites also thrive in dusty environments, so hose down any dirt roads or walkways near your coastal redwood tree to reduce dust levels.

Chemical Control Methods

• Severe scale and spider mite infestations can often be controlled by spraying your coast redwood tree with a 2 to 3 percent horticultural oil solution. Following the instructions on your product's label, mix 5 to 7-1/2 tablespoons of horticultural oil product into a gallon of water. Thoroughly spray the tops and undersides of the leaves as well as the bark. Apply an oil spray only when the weather forecasts don't predict any fog, rain or temperatures higher than 90 degrees Fahrenheit within 24 hours of treatment.