The most common symptom is sickly yellow needles with browned tips, although some needles may have a blotched appearance. Mites feed on needle sap and cause a small white or yellow spot at the feeding site. Many mites feeding give the needle a stippled or rusted appearance. The needle sheath mite gets its name from its habit of feeding in the sheath at the base of the needle. Needles need to be pulled apart in order to see the mites.
Most trees usually support a small population of such mites that causes no visible damage.
Flare-ups often occur on stressed trees or after applications of broad spectrum insecticides that kill mite predators. Damage appears first on the south side of the tree and may or may not spread around to the other sides. The needle sheath mite is a small mite in the family Eriophyidae. These mites are some of the smallest arthropod plant pests known. Their bodies gradually taper toward the end and somewhat resemble a carrot in shape.