Probably bean rust, especially if red powdery spores are visible. Remove every remotely infected leaf, and you can really slow it down.

There's no real "knockdown" treatment, but copper fungicide can greatly slow the spread. Chlorothalonil (Daconil) will protect leaves that have yet to be infected. I don't like using copper regularly because of toxicity concerns.

As for organic treatments, Serenade is listed for bean rust as "suppresses" rather than "controls".. usually means it's best used as a preventative. Actinovate isn't labeled for it. Wettable sulfur is labeled, but has questionable efficacy.

Rosemary, thyme, and clove oil are also listed as OMRI options for bean rust, in the form of Sporan fungicide. Efficacy has been shown only in vitro.

Thanks greentiger87,
I probably won't go the copper spray route, but might try the Rosemary oil spray early next season as a preventive. Will just call this season a learning experience for bean growing.

Thanks for your advice,
Dan

My own unscientific observations is that whenever my plants have had disease like you show, there have been watering issues. Either soil too wet, too dry, wet spots & dry spots together, leaves wet at night, soil goes gets too dry before watering. All this causes stress.

You might want to use the finger method to continually observe the container wetness and notice the plants health at the same time. After doing this awhile you can usually tell just by looking at the plant the state of the soil wetness.

Also, even if my plants were fertilizer deprived, but the soil wetness was good, they didn't develop disease (they just stayed yellow in color and didn't grow much).

Also watering the leaves on a hot sunny day, helps prevent disease. Spore/fungus will start to grow but as the leaves dry in about 1/2 an hour, they die.