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Field Pea Diseases Review: Bacterial Blight and Brown Spot: (06/02/16)

Bacterial blight is generally not considered an economically important disease of field peas in North Dakota, but severe losses to the disease have been reported in neighboring states.

Field Pea Diseases Review: Bacterial Blight and Brown Spot:

Importance.  Bacterial blight is generally not considered an economically important disease of field peas in North Dakota, but severe losses to the disease have been reported in neighboring states.  The disease is caused by a bacterial pathogen; fungicides have not efficacy against bacterial pathogens, and fungicides are NOT recommended for management. However, bacterial blight is often confused with Ascochyta blight, which is an economically important disease that can be managed with fungicides. Consequently, accurate identification of this disease is critical. Bacterial blight can be common when frequent rains occur with conditions that damage plant tissue (hail, high winds).

Symptoms.  Lesions can occur on all above-ground plant parts. Lesions begin as small greasy or water-soaked spots that will quickly turn necrotic. Unlike Mycosphaerella/Ascochyta blight lesions, bacterial blight lesions do not readily cross leaf veins and will take on an angular shape and appearance. Under high humidity, bacterial ooze may be visible from the lesions. Eventually, the centers of the lesions may dry up and fall out.

Disease Cycle and Development. The pathogen is primarily residue-borne but can also be seed-borne. Infection begins when spores produced in bacterial ooze are splashed onto pea growth. Typically, a combination of plant injury (such as from hail or wind-driven soil) and moisture is needed for infection to occur. The disease will progress if frequent rains persist but will slow or stop if dry conditions occur.

Management: The most important consideration when examining peas for bacterial blight is to accurately distinguish it from Mycosphaerella/Ascochyta Blight. Fungicides may be recommended for Mycosphaerella/Ascochyta blight, but are NOT recommended for bacterial blight. Misdiagnosis of these two disease can result in an unnecessary fungicide application, or, an erroneous no-spray recommendation – both situations can be costly.  If Bacterial blight occurs, stay out of the fields when wet to avoid mechanical transmission of the disease.  Because the disease is seed-borne and seed-transmitted, it is advisable to avoid seed lots originating from fields where bacterial blight developed above low levels.

ppth.markell.bacterial blight

Sam Markell

Extension Plant Pathologist, Broad-leaf Crops

&

Julie Pasche

Research Plant Pathologist

NDSU Dept. of Plant Pathology

&

Michael Wunsch

Research and Extension Pathologist

NDSU Carrington REC


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