Watch your plants for spider mite damage. Spider mites are very small so you can’t see them with the naked eye. The first sign of their presence is pale, dirty looking patches of foliage. To check for them hold a piece of paper under a branch that looks suspicious. Shake the branch vigorously and watch for what looks like specks of dust to fall on the paper. Watch these specks closely, if they start to move they are most likely spider mites.
To control spider mites spray the plant with Ferti-lome or Bonide Horticultural Oil. Products containing the active ingredient bifenthrin can also give good control. Good coverage is essential so make sure to spray under leaves. Avoid spraying during the heat of the day. Treat again in a week. Do not spray blue spruce with horticultural oils.