The symptoms of powdery mildew of pea (caused by Erysiphe polygoni) first appears on

The symptoms of powdery mildew of peas (caused by Erysiphe polygoni) first appear on Leaves.
Powdery mildews are easily recognized by the white, powdery growth of the fungus on infected portions of the plant host.
The powdery appearance results from the superficial growth of the fungus as thread-like strands (hyphae) over the plant surface and the production of chains of spores.
Symptoms consist of a light, greyish, powdery growth on the leaves, pods, and occasionally on the stems.