Figure 1. Bacterial blight symptoms on leaves.
Bacterial Blight in S.D. Field Peas
Disease issues have not been a major concern for field pea producers in South Dakota. The dry climate, low acreage and diverse crop rotations practiced by growers have all contributed to reduced disease problems. However, as pea acres increase in South Dakota, this could change. Diseases can be a problem on pea and one disease of emerging importance is bacterial blight.
Transmission & Symptoms
Bacterial blight tends to show up when pea plants are damaged by rain, wind, hail or a late spring frost. Tissue damage to the plant will create a wound and the bacteria will colonize the wound. Symptoms of bacterial blight can appear on the stem, leaves and pods (Figure 2) of the pea plants. All foliar tissue is susceptible. Initial symptoms are small shiny water soaked spots. As the disease progresses these areas can coalesce, and turn brown and necrotic.
In South Dakota, this disease is often seen in young pea plants after a late spring frost. However, as is often the case, if weather becomes warm and dry, the disease does not spread and new growth is often healthy. Damage and yield loss is minimal in these situations. However, there have been isolated situations when the occurrence of strong winds and hail late in the season has resulted in severe damage and yield loss in peas from bacterial blight.
Figure 2. Bacterial blight symptoms on pods.
Identification & Management
It is important to properly identify bacterial blight. Symptoms of bacterial blight can be mistaken for Mycosphaerella or Ascochyta blight, another disease that can affect pea. Mycosphaerella blight is caused by a fungus and therefore can be treated with fungicides. Bacterial blight is caused by bacteria (Pseudomonas syringae pv. pisi or Pseudomonas syringae pv. syringae) and therefore fungicides will not be effective at controlling this disease. This is the reason accurate identification is very important. Unlike Mycosphaerella blight, lesions caused by bacteria are limited by leaf veins. This feature can be seen in Figure 1. In addition, bacterial blight lesions are brown to translucent and this can be helpful at differentiating between these diseases. Copper based chemicals have been used to manage bacterial blight of pea at times. However, there is no data to indicate this practice is beneficial.
For more information on field pea diseases and fungicide efficacy, visit the following sites: