ISSUE 14 August 21, 2008
RUST ON DRY BEANS APPEARING IN ND
The appearance of rust on dry beans has been sporadic this year, but is severe in localized areas in the state. Rust can cause yield loss when severe.
Rust can be identified by small (about 1/8 inch) reddish-brown pustules on leaves. Reddish-brown spores (urediniospores) are produced in the pustules, which can easily be rubbed off with your finger. The ability to rub off spores distinguishes rust from other diseases such as bacterial blights.
Rust can progress quickly in fields when temperatures and moderate, and when heavy dews occur in the mornings. As the season progresses, the rusty-colored spores in the pustules will be replaced by black spores (teliospores), which are hard to rub off. Once the color change of the spores is apparent, disease progression will grind to a halt.
Fungicides can be used to manage rust, and several fungicides are available for rust control, including Folicur, which just received a Section 3 – Full registration for management of rust on beans. The supplemental label is available at http://www.cdms.net/LDat/ld6AK031.pdf. The supplemental label must be in your possession if a fungicide application is made. Other fungicides can be found in the 2008 ND Field Crop Fungicide Guide (PP-622) available at
If fungicide application is something you’re considering, it is vital to keep a couple things in mind. First, be certain your beans are infected with rust, and not something else. We are observing lots of bacteria diseases throughout the state, which cannot be controlled with fungicides. For more information about bacterial disease, including symptomatic pictures, please refer to my article in the last issue of the crop and pest report at http://www.ag.ndsu.nodak.edu/aginfo/entomology/ndsucpr. Secondly, as the season progresses, the likelihood that new rust infections will cause yield loss decreases. As the weather turns cooler rust will develop more slowly and eventually cease when teliospores are produced. Additionally, as beans mature, rust is less detrimental to yield, and thus, fungicides are not economic.
Extension Plant Pathologist