Bean rust usually is observed first as discrete pustules which are filled with cinnamon-brown spores, which leave a dusty brown streak when rubbed. The last bean rust epidemic in North Dakota in the 1990s caused in excess of $10 million in crop losses. Following the introduction of rust-resistant dry bean varieties produced through crop breeding, rust was not a problem until 2008 when a new race appeared which could overcome the resistance. Since the new race was first detected, rust has re-appeared every year. However, the disease has caused little damage due to frequent fungicide applications for white mold (most of the fungicides applied for white mold have some efficacy against rust).
“Between 1996 and 2008, bean varieties with resistance to rust made the threat of a bean rust epidemic in North Dakota very low. However, in 2008 a new race of the pathogen was identified in North Dakota. The new race has the ability to cause disease on the only commonly used effective resistance gene in common varieties. In 2010, the new race spread throughout North Dakota and into northwestern Minnesota. With the spread of the new race, the region is at risk again for the multimillion dollar yield losses caused by bean rust decades ago.
A fungicide application can be a very effective tool for rust management… In rust trials conducted between 2009 and 2011, all fungicides tested reduced rust severity… Because of this, a secondary benefit to a fungicide for white mold (which occurs at early bloom, R1-R2) is that the application may offer some measure of rust protection.
A fungicide application is most effective soon after the disease is found, making scouting for the disease critical.”
Authors: Markell, S., Olson, L., and Acevedo, M.
Affiliations: NDSU Department of Plant Pathology
Title: Dry edible bean rust
Source: Plant Disease Management. NDSU Extension Service. January 2012. Available at: http://www.ag.ndsu.edu/pubs/plantsci/pests/pp1601.pdf