My zucchini and string bean crops are being grown on a deck in pots. Both have unique forms of brown spots, wilting dried out leaves and yellowing of the leaves. The string bean plants are producing beans, but the leaves are so spotted with browning. The zucchini leaves are yellow, have crisp brown edges but continue to produce beautiful zucchini at a slow rate. I have tried Neem oil, baking soda mixes and garlic mixes. Nothing works.
Yellow and Brown Leaves
Certified GKH Gardening Expert
If the leaves were yellowing first, it may have started with a watering issue. Either to much or to little.
Stressed plants tend to invite insects or disease.
Neem Oil is my recommendation. You may want to reapply once a week.
Here are some links with more information.