A New Disease on Corn Observed Across Southern and Mid-South States
Published: 06/26/2024
DOI: doi.org/10.31274/cpn-20210721-0
CPN-2017
Since 2020, there have been increased reports of new leaf spotting on corn in some southern and mid-southern states. Symptoms include tiny (less than 1 mm) tan to brown spots with a darker brown margin (Figure 1). The associated leaf spots can appear as individual spots, that later occur in small, tight clusters, which can coalesce and cover large sections of the leaf surface (Figures 2 and 3). In general, the spots are more commonly concentrated along the mid-rib and veins (Figure 4). Symptoms are generally more noticeable on field edges.
Figure 1. Newly observed leaf spots appear as tiny tan to brown spots with a darker brown margin.
Kiersten Wise
Figure 2. Clustered leaf spots on corn.
Kiersten Wise
Figure 3. Lesions can coalesce and cover large sections of the leaf surface.
David Langston
Figure 4. In general, the spots are more commonly concentrated along the mid-rib and veins.
David Langston
Initially the symptoms were thought to be due to an abiotic disorder. However, in 2022, Virginia Tech pathologists began investigating a potential fungal pathogen believed to be the cause of these symptoms after observing that symptoms were reduced in situations where foliar fungicide applications occurred. Similarly, foliar fungicide applications appear to reduce disease in fungicide trials conducted in several states. The suspected pathogen has been observed on symptomatic leaves, and undergone laboratory experiments to confirm its identity, including microscopy and DNA sequencing, but pathogenicity tests are still pending. Preliminary results indicate that the disease is caused by a fungus. It is possible that symptom expression is associated with a physiological crop shift from vegetative to reproductive stages as symptoms have appeared after tasseling (VT) and during grain fill (R1-R5), and most notably developing during July and August each year. Symptoms have not been observed during vegetative growth stages of corn. Symptoms and severity vary depending on hybrid.
To date there have been no observed or reported yield losses associated with these symptoms, but the impact on yield continues to be investigated. To distinguish between this new disease and other foliar diseases, like Curvularia leaf spot (Figure 5), we recommend submitting samples to a diagnostic laboratory. Research on this new disease and its causal organism are underway.
Figure 5. The abiotic disorder can also resemble symptoms of Curvularia leaf spot shown here.
Kiersten Wise
Acknowledgments
Authors
David Langston, Virginia Tech; Dr. Mychele Batista Da Silva, Virginia Tech; Kiersten Wise, University of Kentucky; Bob Kemerait, University of Georgia; Trey Price, LSU AgCenter; and Tom Allen, Mississippi State University.
Reviewers
Martin Chilvers, Michigan State University and Andrew Friskop, North Dakota State University.
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