Ranging in color from green to orange-red, spruce spider mites are conifer-loving pests that overwinter as orange eggs at the base of needles and twigs. After hatching and molting several times, the adults mate and lay eggs. There can be six to eight generations each season, depending on temperature. The spruce spider mite is most active during the cooler temperatures of spring and fall, and may discontinue its feeding and reproductive activity when temperatures rise during the summer months.
Spruce spider mites feed on more than 40 different types of conifers, especially Alberta spruce, as well as arborvitae, fir, hemlock, juniper, and other spruce species.
These sap-sucking pests deprive trees of nutrients, causing their needles to fleck and turn yellow. Signs of a worsening infestation include remnants of silk webbing and shed skins, as well as brown needles, premature needle drop, and branch or tree death.
Unless treating sensitive dwarf Alberta spruce or Colorado spruce, apply an appropriate miticide before bud break to reduce overall populations and again in late fall if necessary. Talk with a certified arborist about alternative treatments when miticides cannot be used.