How to Identify Shrub Disease

Examine carefully the diseased shrub leaves, bark and stem.
Use a magnifying glass to look for evidence of insect-like material such as plant aphids or scale insects. This can be done without a magnifying glass in many cases.

Look for possible evidence of mold attack---typically manifest by black or gray dots or spots.

Look for browning of the leaves, leaf drop and shedding, which can be signs of drought damage. Excessive moisture and mold attack can do this also.

Break off, or snip off, a piece of the plant.
Place the diseased portion in a plastic bag for transport to a plant specialist at a nursery or hardware store. The diseased specimen can be checked, and possible, suitable chemicals recommended.