Bacterial leaf streak (BLS) is particularly prevalent across Iowa this growing season. This past week I received numerous emails and texts with photos. I’m not overly surprised we are seeing BLS because we have had numerous storms pass through the state.
BLS can be easily misdiagnosed as gray leaf spot (GLS). Is that a problem? Yes! Fungicide applications will have no effect of on BLS, but they will control GLS.
Differentating BLS from GLS
Probably the easiest way to differentiate BLS from GLS at this stage of growing season (V16 through R3) is where the symptoms are observed.
- BLS is observed primarily in the mid- to upper canopy of the corn crop. It is rare to observe BLS in the bottom of the canopy in mid-season.
- GLS will always start on the lowest leaves of the canopy, usually around tasseling, and move upwards through the canopy as grainfill progresses.
Regarding the symptoms:
- Lesions of BLS are tan to brown, narrow and long (1/2 to several inches) (Figure 1). They tend to have wavy margins which differentiate them from GLS lesions which are rectangular and have straight edges (Figure 2).
- Also, if you hold symptomatic leaves up to the light, the lesions of BLS often have very bright yellow halos (Figure 3).
Figure 1. Narrow, tan lesions of bacterial leaf streak on corn. Note the wavy edges.
Figure 2. Rectangular lesions of gray leaf spot. Note the straight edges.
Figure 3. Bright yellow halos surrounding bacterial leaf streak lesions.
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- Professor of Plant Pathology and Microbiology
- Extension Field Crops Pathologist