Like Alison remarked last year, this is another big season for bacterial leaf streak (BLS). I’ve seen low levels in numerous fields, but one field yesterday stopped me in my tracks, an obvious susceptible hybrid. A casual observer may mistake BLS for gray leaf spot (GLS). While GLS can be effectively managed with fungicide, BLS cannot. Take care to distinguish between the two when scouting fields before fungicide applications in the coming weeks.
BLS is more likely to occur in the mid or upper canopy and will continue to move through the corn canopy following rain events, while GLS begins in the lower canopy and moves up as the season progresses (Figure 1).
BLS symptoms include narrow lesions that could be very short to several inches long (Figure 2). The key way to distinguish it is its wavy margins and bright yellow halos when backlit (Figure 3). GLS will have straight edges that are bound by the veins in the corn leaves (Figure 4). This time of year, it would be unusual to find more than a few GLS lesions clustered together on a leaf, so the discovery of many lesions on leaves is another sign of BLS rather than GLS.
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- Field Agronomist in Central Iowa