Spider mites coat the plant with a fine webbing and they are really hard to see.
On Cypress trees, the affected leaves can usually be readily seen because dust or dirt attaches to the webs and makes them more visable, but by the time you notice that, a lot of damage has been done.
If you suspect you might have spider mites, take a white sheet of paper to the affected plant and gently shake or tap it over the paper, you should see very tiny reddish specks moving around on the paper, those are the mites.
Spray the trees or plants with a spider mite controlling systemic insecticide. Two to three applications are usually needed to kill these guys, as they are difficult.
Always make sure the plant is well watered the day before you start spraying.
Always remember to water the plant throughly and allow several hours for the water to be taken up into the plants cells prior to applying any insecticides or fertilizers.
Applying any chemicals to a plant with very dry soil will burn the leaves or maybe kill the entire plant.
Always spray in the morning or late evening when there is no wind and the sun is not up very high.