Rust on beans Uromyces appendiculatus
IDENTIFICATION — Rust can live in your soil for years. When the conditions are right (mainly long cool and wet periods) the fungus will infect any green part of the bean plant. It rarely kills, but will reduce the harvest.
CONTROL — The best way to avoid the problem is to choose a resistant cultivar, such as ‘Kentucky Wonder Rust Resistant’, ‘Jade’ or ‘Provider’. Make sure the beans have excellent air circulation and plan for the crop to ripen during the heat of summer. If you’ve had a rust problem in the past, spray or dust the leaves once a week with sulfur. Start as the leaves emerge and continue until the beans bloom.
Since splashing water spreads the spores, don’t use overhead sprinklers. If you see rust on the leaves as the beans ripen, avoid picking after a rain or early on a dewy morning. You’ll be spreading the spores as you pick the fruit. While the beans don’t look very appetizing, you can eat them if you wash off the spores.