Robert M. Harveson, Extension Plant Pathologist University of Nebraska, Panhandle REC, Scottsbluff
Introduction
Dry beans in Nebraska may be affected by a complex of different bacterial diseases. There are four commonly encountered diseases: common blight, halo blight, brown spot, and wilt. These diseases have had major impacts on dry bean production wherever dry beans are grown, and significant efforts have been made to manage them.
Each disease is favored by similar environmental conditions, including high moisture, and factors such as storms, planting non-certified seed, proximity to infected volunteers, and equipment or irrigation water that cause wounding and move pathogens and infected residue between and within fields. However, they do differ in the respective temperatures favoring development for each disease: halo blight - less than 80° F; brown spot – less than 85° F; common blight – greater than 80° F; and wilt – greater than 90° F.
Common blight
Common blight is caused by Xanthomonas axonopodis pv. phaseoli. The disease was recognized for the first time in the U.S.in 1892 and shown to be damaging to beans from both New Jersey and New York. Curiously, the pathogen was demonstrated to be internally seedborne at this time before it was formally identified and named in 1897
The disease has plagued Nebraska producers since dry beans were first introduced in the 1920s. It is considered to be a major problem throughout the world wherever beans are grown. It has often been highly destructive in this region during extended periods of warm, humid weather, causing reductions in both yield and seed quality. Losses have been reduced within the last 30 years because many of today’s cultivars now have some level of resistance to the pathogen, due to the work of Coyne and Schuster in Nebraska beginning in the 1960s. Further improvements for managing this problem were realized when seed began to be produced in arid areas of the western U.S., instead of being locally produced near commercial production fields in western Nebraska.
Halo Blight
Halo blight is a bacterial disease caused by Pseudomonas syringae pv. phaseolicola. This disease first appeared in New York State (U.S.) in the early 1920s, and became a serious problem very rapidly. The transmission of the pathogen through seed can partially explain its wide and rapid distribution.
At the same time that halo blight was identified in the U. S., a disease of kudzu was being studied by Florence Hedges in 1927. She described and named this pathogen Bacterium puerariae, but later determined that the kudzu disease was incited by the same pathogen that caused halo blight. Therefore, it has been presumed that the bacterium was imported on the kudzu vine from Japan and assumed to have been introduced in 1876 at the Philadelphia Centennial Exposition, before later becoming an important pathogen of beans.
Halo blight, like common bacterial blight, has been found in Nebraska for more than 70 years and is also considered to be a major problem throughout the world where moderate temperatures occur during bean production. Losses in the Central High Plains have been reduced due to the availability of genetic resistance to the pathogen. Several popular cultivars have good levels of resistance to common and halo blights, but are more prone to infection by rust or white mold.
Brown Spot
Bacterial brown spot, caused by Pseudomonas syringae pv. syringae, was first described by Walter Burkholder in 1930 as a new disease of beans based on laboratory investigations of diseased specimens from New Jersey. It was initially considered a disease of rare occurrence in the U.S. until severe outbreaks occurred in Wisconsin snap and lima bean fields in the mid 1960s.
Bacterial brown spot is a more recent disease of dry beans in Nebraska than halo and common bacterial blight. It was first observed from western Nebraska dry bean fields on a limited basis throughout the late 1960s. Epidemics have occurred sporadically, but the pathogen’s presence has been increasing in incidence and damage for the last 5 years in western Nebraska. When the disease occurs today, it can be very damaging due to the lack of resistance in modern commercial cultivars.
Wilt
Wilt is caused by Curtobacterium flaccumfaciens pv. flaccumfaciens, and was first reported from a South Dakota navy bean field in 1922. It then became one of the most problematic bacterial diseases in the USA, particularly throughout the irrigated high plains and Midwest. Bacterial wilt was commonly found in dry bean production in western Nebraska during the 1960’s and early 1970’s but promptly disappeared and was not observed in Nebraska until its reemergence in the early 2000s. Recent surveys of Nebraska production fields have shown that wilt was the most commonly identified bacterial disease over entire growing region, suggesting that it currently is the most serious and important of the bacterial diseases for focusing management efforts.