Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu
Bacterial diseases have started to pop up in some snap bean fields. There are three main bacterial diseases that can be encountered on beans: bacterial blight, halo blight, and bacterial brown spot. These pathogens can infect foliage and pods and can be introduced by infested seed or residue. Spread of the pathogens occurs through splashing rain, overhead irrigation, wind, or surface water. All three pathogens enter plants through wounds (i.e. insect damage, wind, sandblasting) or natural openings. Although several important characteristics of these diseases differ (Table 1), management is similar.
Table 1. Characteristics of three common bacterial diseases on snap beans
Figure 1. Examples of symptoms caused by Halo blight (A-B), Bacterial brown spot (C-D), and Bacterial blight (E). Images obtained with permission from The Bugwood Network and Forestry Images Image Archive and Database System (www.bugwood.org).
To manage these diseases within the season, growers should avoid excessive overhead irrigation as this may spread the pathogen within the field and increase disease severity. Do not scout or cultivate infected fields under wet conditions. Sanitize planters, harvesters, or other equipment before moving from an infected field to an uninfected field.
These bacteria can grow on the surface of foliage, so the use of the following when incidence is low can slow disease progress: fixed copper-1.0 lb. a.i. per acre or Cueva 0.5-2.0 gallons per acre. Thorough coverage is essential. Apply on a 7 to 10-day schedule through harvest. Remember the label is the law.
Between seasons it is important to use certified, disease-free seed. Practice good sanitation for all equipment and storage areas. Clean tillage and/or a 3-year rotation away from beans, soybeans, and lima beans can reduce inoculum levels within a field. Weeds may serve as reservoirs for these diseases and should be properly managed.