The needles are stippled yellow and dirty. A fine silken webbing may be on the twigs. Needles may turn brown and fall off. To check for mites, hold a sheet of white paper underneath some stippled needles and tap the foliage sharply. Minute specks the size of pepper grains will drop to the paper and begin to crawl around.
Hose down plants frequently to knock off webs and mites. Apply an insecticide labeled for these pests.