Identification

• Spider mites are tiny arachnids about ½ millimeter in length. Young mites are green, and darken with age. Their coloration can make the spruce spider mite difficult to see against the redwood's foliage. Spider mites lay oval or round reddish-orange eggs, which may be easier to identify on the tree. To determine whether a redwood is infested, hold a sheet of paper under a branch and shake the branch. Any mites will fall onto the paper, making them easier to see.
  
  

Damage

• Spider mites hatch in spring and begin feeding on the needles. The foliage initially develops a mottled appearance, then turns yellow and bronze. Spider mite damage may cause dawn redwoods to drop their needles early. In serious cases, they can partially defoliate the tree or kill twigs and branches. Severe infestations on young, stressed trees can even kill the host.
  
  

Control

• Several predators naturally control spider mites, including lacewings, ladybugs, midges, predatory mites and the rove beetle. Many beneficial insects are available for purchase online. Try these eco-friendly creatures before using chemical control methods. If chemical means are required, spray trees with dormant oil spray in fall, or summer oil or insecticidal soap during the growing season. The University of Minnesota Center for Urban Ecology and Sustainability recommends miticides, including hexygon, bifenazate and clofentazine, as less toxic to beneficial insects than other pesticides.
  
  

Considerations

• Small populations of spider mites on a dawn redwood may not require control. While these creatures can cause some aesthetic damage, they don't usually hurt healthy trees unless their numbers increase significantly. Monitor infested trees and keep them well-irrigated to encourage mite resistance. Apply pesticide treatments only when the mites begin to take a toll on the tree.