When the leaf becomes heavily infected, it shrivels and falls from the plant. The fungus exists between crops in the form of spores which initiate infections in the following crop. Under these conditions, an infection of bean rust can produce a new crop of spores in 10 to 15 days. Although Uromyces spores may blow long distances and infect plants where no beans have ever been grown, it has been shown that when one crop of beans follows another in the same field, the amount of rust inoculum is increased so that the following crops may be damaged severely. In Kentucky, rust is much more common in late summer and early fall than any other season.
Crop rotation is the first suggestion for control.
Spraying with approved fungicides at regular intervals, starting when the disease first appears or when advisories are issued, will give effective control. Some bean varieties are resistant to some races of the rust fungus. These varieties are listed as rust resistance in seed catalogs. Consider them where space doesn't permit long rotations and where fungicides will not be used, especially in late summer plantings. Contact your County Extension Office for the currently recommended chemicals.