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Rust of Dry Beans
Under normal weather conditions, the disease develops too late in the growing season (about early pod striping) to cause serious damage. Rust attacks when growing conditions are cool (60-75 F), and moist with frequent, prolonged dew or rains.
Rust is most serious on late planted beans, on heavily fertilized beans, on beans delayed in maturity by weather damage such as hail, or on beans planted on or adjacent to old bean ground.
Rust, caused by a fungus (Uromyces appendiculatus), is found mainly on bean leaves. Severely infected plants are defoliated. The most obvious symptom of the rust disease is the presence of pustules containing rusty-colored masses of spores. The rusty-colored spores (ureodospores) are the summer spores and spread the disease from plant to plant. Hundreds to thousands of spores are produced in each pustule, and new pustules arise about 10 days after infection.
Weather is important in rust epidemics. Rust uredospores germinate best at about 63 F (17 C). Poor germination of spores at 81 F (27 C) may account for reduced spread of disease at high temperatures. Free moisture (rain, dew) or high relative humidity (96 percent plus) are essential for infection. When moisture and temperature are favorable for more than eight hours and spores are present, infection occurs.
Maneb and chlorothalonil (Bravo, Echo) provide effective control of rust if applied early, when rust is first detected.
Most older pinto varieties, as well as small reds and pinks are susceptible to the current races of rust. Many newer pinto varieties have good resistance to the current rust races, as do many of the newer navy varieties, blacks, cranberries, and dark red kidneys. Rust reactions of dry bean varieties are listed in Circular A-654, North Dakota Dry Bean Performance Testing.
Many races of rust are present in the area. Monitoring for rust is important, even on varieties resistant to the current races, as new races might arise capable of attacking resistant varieties.
For more information see the Fungicide guide at http://www.ext.nodak.edu/extpubs/plantsci/pests/pp622w.htm or see http://www.ext.nodak.edu/extpubs/#plantsci
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