Scouting for spider mites

Spider mites are small!  From left to right, a spider mite is compared to a collembolan, a thrips, a cotton aphid, and the head of an insect pin.

Mites should be scouted on a weekly basis.  It is essential that plants for sampling be chosen randomly. In other words, do not chose plants based on visible mite damage.  Take samples from 25 to 50 paces into the field.  From a randomly-chosen plant, collect a mainstem leaf; the bottom leaf when plants have less than 9 mainstem leaves, or a mainstem leaf approximately 6 nodes below the terminal when plants are larger.  Using a 10x hand lens, examine the entire underside of the leaf for mites.  Approximately 30 plants, at least 20 meters apart, should be sampled from various areas of the field.  If the percentage of infested plants is 50% the field may need to be treated (6).
 

A 10x hand lens or linen tester is extremely useful in making counts of spider mites.  Before a field should be treated, a random sample of 30 plants should show that 50% of the plants are infested with live mites.

Spider mite colonies usually start at the junction of the main leaf veins.