Spider mites damage cotton by sucking the contents of epidermal cells, and in the case of  T. turkestani by injection of toxins.  Feeding results in water loss, reductions in photosynthesis, and when extensive and prolongued can result in defoliation.  When severe, a total loss of squares and fruit may result.  The first sign of spider mites damage is a light tan or yellowish russeted discoloration of the underside of the leaves, particularly at the junction of the main veins.  Often infested areas of a field can be spotted from outside of the field as reddish or yellowish areas in the field.  When T. turkestani is involved, leaves may turn bright red and orange.
 

Moderate mite populations cause this russeting on the underside of leaves.	Cotton leaves infested with spider mites can turn red and orange.	Severe mite infestations can cause defoliation.  This field is in trouble!