Pseudomonas syringae pv. syringae
Lesions appear initially as lime-green to olive-colored translucent discoloration running along the leaf veins of lower leaves. They also gradually start to show in the upper foliage. In optimum weather conditions, these lesions expand longitudinally and tend to coalesce. Bacterial ooze is sometimes perceptible in infected tissues at early stages of the disease. With age, the lesions develop brown necrotic stripes in their centers, that later dry and fall out, giving the leaf a ragged appearance. In some susceptible corn varieties, chlorotic striping of the whorl leaves and distortion of the upper nodes of the plant can be observed.
Symptoms depend greatly on the strength of the pathogen, the corn variety and the environmental conditions. The bacteria survives in crops debris in soils, on numerous alternative hosts and weeds and on volunteer crop plants. It is disseminated between plants by irrigation water, wind, or contaminated workers and equipment. The bacteria enters the plant through natural openings or wounds. It can withstand temperatures between 0 and 35 °C, but it thrives in the range 25-30°C. The disease is worst during periods of wet humid weather. When the disease occurs early in the season, some farmers choose to destroy the entire crop by disking.
To this day, no effective organic treatment is available. Alternative options for control of bacterial spot in corn are limited to the use of preventive measures and good field practices.
Always plan an integrated pest or disease management, with preventive measures and biological treatments if available. Currently, chemical treatment is limited to copper or copper combined products. Many sprays are only marginally effective, making the disease very difficult to control once an epidemic is underway.