Bacterial leaf streak (BLS) is a new bacterial disease affecting corn in the United States.  The disease has been present in Nebraska corn fields at detectable levels since 2014, but was only recently positively identified.  The disease has been detected in nine states , but has not been detected East of Illinois.

BLS symptoms are limited to the foliage.  Lesions are narrow and elongated, with wavy edges (Fig 1).  When backlit, a bright yellow halo is evident around the leaf margins (Fig 2).  Lesions can expand under favorable conditions to affect large areas of the leaf, and may resemble other diseases such as Grey Leaf Spot (Fig 3), Northern Corn Leaf Blight, and Corn Leaf Spot.  Abiotic issues, such as nitrogen burn, and hybrid genetics, can also resemble BLS.    Disease symptoms can be observed from early vegetative stages through later reproductive phases, and begin on lower portions of the plant first in many, but not all, instances.  Sometimes symptoms appear after heavy rain or windy conditions.  Field, sweet, and popcorn can be affected.

Fig 1. Bacterial leaf spot on corn. Note the elongated lesions. Photo K Broders

Fig 1. Bacterial leaf streak on corn. Note the elongated lesions. Photo K Broders

 

Currently little is known about the disease cycle of BLS.  We do know that the disease is caused by a bacterium,  Xanthomonas vasicola pv. vasculorum.  We assume that the pathogen may overwinter in corn debris or volunteer corn.  Spread of the pathogen likely occurs through irrigation, flooding, and heavy rain/wind events.  Wounds are not required for infection, as the pathogen infects directly through stomata on the leaves.  Disease has been observed most frequently in fields of continuous corn, but also has been detected in fields rotated with other crops.  So far, it appears that disease severity in affected fields is most severe when overhead irrigation occurs during hot weather.  Under these conditions, severity can approach 30%.

Fig 2. When backlit BLS lesions have bright yellow, wavy margins. Photo K. Broders

Fig 2. When backlit BLS lesions have bright yellow, wavy margins. Photo K. Broders

 

Management

Currently there are few data on yield impacts.  As with other corn diseases, yield losses are expected to be negligible if they occur later in plant development (after R3) or if extensive blighting does not occur.

 

Fig 3. Other diseases and conditions can resemble BLS. For example, Grey Leaf Spot. Photo N. Kleczewski

Fig 3. Other diseases and conditions can resemble BLS. For example, Grey Leaf Spot. Photo N. Kleczewski

 

The key with BLS is understanding that fungicides will not have an effect on this disease.  It is essential that suspect samples are sent to your local Plant Disease Diagnostic Clinic for proper diagnosis in the lab.   In Delaware send samples to Nancy Gregory- information can be found by clicking here