Spider Mites are one of the most damaging pests to most varieties of Spruce, Arborvitae, and other conifers. Mites suck sap from individual needles, causing a ‘stippled’ appearance as the chlorophyll disappears. The damaged inner needles begin to yellow and eventually turn brown and fall from the tree. It is important to note that Mites will not attack first-year candle growth, but they will attack that new growth the following year.
Affected plants that were originally full, thick conifers (often planted as natural privacy screens) will begin to thin out to the point that you can see right through them, no longer providing the intended privacy. These plants then eventually die.
Mites enjoy the cool, damp weather that Illinois provides in spring and fall. Left unchecked, they build up in tremendous numbers, multiplying by the thousands every 10 to 17 days!