I've started wisteria plants from seed. They have been growing just fine, but now I see on one of the plants, its leaves have very small brown specks and the color or the leaf has gone from dark green to a yellowish green. Any ideas?
This could be a leaf spot fungus on your vine.
Removal of the leaves effected is recommended.
Make sure you have good air circulation around the plant and that the soil is moist but not soggy.
These articles have more information.