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Bacterial blight


© Iowa State University

Pathogen(s) causing disease:

Pseudomonas savastanoi

Symptoms:

Angular lesions with reddish-brown centers and water-soaked margins surrounded by yellow halos appear on leaves in the mid to upper canopy. Lesions grow together to produce large, irregularly shaped dead areas, which fall out, causing leaves to appear tattered. Young leaves are most susceptible to blight infection.

Conditions:

Typically an early-season disease. Occurs when wind or splashing water droplets from plant residue on the soil surface to the leaves carry bacterial cells. The bacteria enter the plants through stomata and wounds on leaves. In order for infection to occur, the leaf surface must be wet. Seedlings may be infected through infected seed.

Management:

Scout V2 through R6 in fields that have received heavy rains. The best management tool is to prevent disease establishment through genetic resistance. Cultivars that are not highly susceptible to the disease should be considered for planting. Crop rotation can be an effective method to avoid inoculum from a previously infected crop. Incorporating crop residue by tillage will reduce the amount of inoculum available in the spring to infect plants but there are moisture and erosion issues to be considered. To prevent the spread of disease, limit cultivation to times when the foliage is dry. Copper fungicides are labeled for control of bacterial blight on soybeans but need to be applied early in the disease cycle to be effective.

Sources:

U of NE
ISU

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