Monitor for adults and eggs of spruce spider mite (Oligonychus ununguis) on conifers with a history of mite damage (Abies, Picea, Thuja). These are COOL season mites that will feed on current seasons’s foliage well into the fall. In fact, fall is a pretty important season for this mite species as they can feed way up until the end of November, depending on the temperatures.
A lot of horticulturalists don’t realize it, until damage from fall feeding can be seen months later….in early spring. Infested plants have a slight grey-ish or dull cast to them from a distance.
Monitor lower branches, on the North and East side of the tree, this is where most of the feeding damage is done. Shake branches over a flat white surface and look for tiny moving “specks”. You will need a hand lens to make out their light brown heads and legs and their black backs. You can also just harvest short twigs from this years growth from inside the canopy and examine them closely with your hand lens. Miticides (e.g. Floramite, Vendex) will be effective against both nymphs and adults where populations are very active.
Spruce spider mite eggs appear as very tiny, round, reddish-brown spheres that adhere to the UNDERSIDES of twigs and foliage this time of year. They are not susceptible to miticides.
Once the colder weather comes, spruce spider mites turn from tan and black to orange and black. And, I learned recently that they can change colour when you are trying to photograph them individually and you put them in the fridge for a while to slow them down 🙂
While you are monitoring, look for faster moving, pale tan coloured mites that could be feeding on the spruce spider mites. Predatory mites can sometimes help suppress populations of phytophagous mites, so keep an eye out for them when making pest management decisions.