Remove leaves by pulling downward so that the petiole remains attached to the leaf. Place leaves in a dry paper bag and immediately label the bag so that you will know where it came from. Wash the leaf samples while they are still fresh, before they wilt. If a large number of samples are involved they can be stored overnight in a cold storage, refrigerator or ice chest to keep them from drying out. Use distilled water, available at most drug stores, for washing and rinsing the samples.
Shake leaves to remove excess water and immediately rinse the sample in clean distilled water.
Shake again to remove excess water. Spread out sample on clean paper towels until leaf surfaces are dry. Transfer sample to labeled paper bag, with top open, and dry at room temperature until the leaves are brittle. Sample healthy leaves between July 1st and August 30th. These should represent the average condition of the planting, and should not be damaged by disease, insects, weather or mechanical injury.