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Dry Bean Guide Diseases in dry beans are caused by different pathogens. There are bacterial, fungal, viral and nematode pathogens that can cause diseases in dry beans. If the proper environmental conditions exist; diseases can decrease dry bean yield and quality. It is critical that dry bean diseases be managed to avoid or minimize loss from them. The disease triangle consists of the pathogen, host, and environment. These three factors all have to interact to produce the disease. You can have some influence on the disease by using good management techniques such as : 1) Crop Rotation 2) Planting Quality Seed 3) Sanitation ( i.e. - tillage ) 4) Planting Resilient Varieties 5) Protection ( i.e. Fungicide Spraying ) 6) Cultural Practices ( i.e. - not cultivating dry beans when wet) Most common diseases in the MN/DAK area: a) White Mold Fungal disease that attacks dry beans and other crops such as sunflower. white mold needs wet conditions ( saturated soils 10 - 14 days prior to bloom, high humidity, and continuous wet foliage ), cool temperatures and dead bean flowers and leaves to get started. White mold appears as water soaked spots and becomes covered with a white cottony mass. Plant parts wilt and die above the point of infection on the stem. The stems will appear bleached when the fungus dries out. Sclerotia ( hard black irregular shaped bodies) will form to become the overwintering stage of the fungus. the Sclerotia will overwinter in the soil and germinate next year. Try to avoid white mold by using a three to four year crop rotation and other crops in your rotation that are not susceptible to white mold. Preventative spraying for white mold on a timely basis hands generally given positive results. Methods to control white mold - Thorough coverage with a labeled white mold fungicide is essential to protect the bean plant. Fungicides recommended by Central Valley Bean Coop can be found HERE. Read the fungicide label to determine the correct time to apply the fungicide you are using. In order to achieve the best results from the fungicide; it is recommended that the treatment reach the base of the plant. The fungicide when applied to t he base can move up the entire plant and help protect it from the white mold. Crop rotation is important to limit the Sclerotia build-up in the soil. Manage your soil nitrogen levels to avoid excessive plant growth. Plant rows in the direction of the prevailing winds to aid in keeping the foliage dry. Planting varieties that are upright may also be beneficial. b) Rust in Dry beans Rust is a fungus that can infect dry beans. To infect the rust fungus needs extended wet periods that keep foliage damp and cool to moderate temperatures. Rust first appears as a small slightly raised white spot on the upper leaf surface. The spot will enlarge to appear as a slightly raised rust-orange spot encircled by a yellow halo on the upper part of the leaf and when you look at the underside of the leaf you will see a larger raised rust-orange postule that can be wiped off. Rust has a 10 to 14 day reproductive cycle and can continue to regenerate if the conditions are favorable. If Environmental conditions are right; rust ca move very rapidly thru your dry bean crop. Rust will partially or totally defoliate the bean plant, leaving a plant unable to maximize its full yield potential. Early detection is important, so timely fungicide applications can protect your crop. Crop rotation and tilling in the bean trash can help control next years rust pressure. There are some pinto varieties that are tolerant to the existing races of rust: Maverick, Winchester, Remington and Buster. Races of rust can and do change. It is important to monitor even the fields planted to the tolerant varieties as rust races can and do change. Most navy bean varieties are generally more tolerant to rust than the pinto varieties. c) Root Rots Root rots are a fungus that can infect dry beans. Specific root rots; Fusarium, Pythium, and Rhizoctonia, are soil borne diseases. Crop rotation is an important management tool in keeping root rots in check. Try to avoid sugar beets in close rotation with dry beans if you have a Rhizoctonia build up in the soil. Incorporate your bean trash so it can breakdown before next years planting. Plant seed that has been treated with a labeled fungicide to help prevent early season infection from root rots. d) Anthracnose Anthracnose is a fungus disease that can infect dry beans. In 2000 Anthracnose was observed in Manitoba. To our knowledge, the disease has not been reported in the MN/DAK area. Anthracnose can be seed-borne or can overwinter in the infected bean debris. Usually Anthracnose is not a problem in semi-arid growing areas. The semi-arid areas have been a source of seed for a number of years. It is important to know your seed source. At present your best way to manage Anthracnose is by planting seed from a reputable known source. Knowledge and/or foliar applications is limited as of this writing. Anthracnose develops when temperatures are cool to moderate, long periods of high humidity and heavy dews or free-standing water on the foliage and pods. Anthracnose can easily be spread by rain storms and moving through a field that has wet foliage with equipment or yourself. General symptoms of Anthracnose appear on the underside of the bean leaves as a linear or angular dark-brick red to black lesions or slightly sunken cankers on leaf veins. These same symptoms may be noticed on the upper leaf surface. A sever infection can cause leaf tip and edge burning. If the infection progresses it can kill the entire leaf and growing point. Pod infection produce a round reddish-brown to black spots which develop into a light colored canker. The canker is usually surrounded by a dark brown to black border. If conditions are moist, a mass of pink to beige fungus spores can be produced. As the cankers dry down they will turn dark with age. e) Bacterial Blights Common Blight, Halo Blight and Bacterial Brown Spot are the common blights seen in the MN/DAK area. Leaf and pod lesions, defoliation and shrunken discolored seed are the visible effects of the bacterial blights. Bacterial blights are spread by rain splash and driving winds. Blights can overwinter on the bean trash and can be seed borne. Plant quality "Western Grown" or "Certified Seed" that has been laboratory tested to keep field blight levels low. Dry bean seed should be treated with Streptomycin Sulfate to kill any surface bacteria on the seed. Crop rotation is a good management tool. Never plant dry beans back to back on the same field, use at least a 3 to 4 year rotation. Bury the bean trash so the bacterial blight does not overwinter well. Avoid cultivation when the bean foliage is wet. Copper sprays can hold the blight in check until the weather conditions favor the disease. Spraying copper, every 7 to 10 days may not prove to be cost effective in the MN/DAK area. |
