What's Cropping Up? Blog

Articles from the bi-monthly Cornell Field Crops newsletter

Alternaria leaf spot of wheat in New York

Michael R. Fulcher, Jaime A. Cummings, and Gary C. Bergstrom
School of Integrative Plant Science, Plant Pathology and Plant-Microbe Biology Section, Cornell University

Fig 1. Foliar lesions photographed during grain filling. The bleached white centers and dark irregular margins are unique to this wheat pathogen. Photo by Gary Bergstrom.

A new foliar disease of wheat was found in New York in summer 2015. The disease was spotted in Monroe County at a regional wheat variety trial conducted as part of the Cornell Small Grains Project under the direction of Mark Sorrells. The Cornell Field Crops Pathology Program lead by Gary Bergstrom first identified the pathogen and has continued to study this disease. Symptoms are distinct from other foliar diseases of wheat, and lesions resemble those of scald on barley, i.e., with bleached white centers and dark borders. Damage occurs primarily on leaves but can also be seen on spikes and occasionally stems (Figures 1-3). We are calling this new disease ‘Alternaria leaf spot’ as it is caused by fungal isolates shown by matching DNA sequences to belong within the diverse Alternaria infectoria species group. This group includes fungi with no demonstrated pathogenic ability as well some wheat pathogens known to cause disease outbreaks that range from minor to severe in other countries. Yet no previous report of fungi in this species group has been associated with the very distinctive foliar lesions we have observed in New York.

Fig 2. Bleached glumes with the characteristic dark margins on a wheat spike. Photo by Jaime Cummings.

Alternaria leaf spot was confirmed in Monroe County, at two separated sites near Lake Ontario, during the past two growing seasons. We are now confirming a likely reoccurrence in Monroe Co. in 2017. We are also using comparative DNA sequencing to determine if the same pathogen was the cause of unusual glume symptoms observed on winter wheat in Jefferson County, also near Lake Ontario, in 2015. Though not confirmed outside of a small geographic area, the disease has occurred in both variety trial plots and commercial fields. All the varieties observed at these locations, over 60 soft white and red winter wheats, have been susceptible to the pathogen. Damage to the flag leaf in severely impacted fields may be significant enough to cause a reduction in yield. However, the disease seems to require an unusually long period of leaf wetness to develop, which may explain why we are finding the disease in maritime environments with persistent fog and dew. No information exists at this time about the efficacy of foliar fungicides against this pathogen and no fungicides are registered for this use. Further research into the pathogen’s complete distribution, inoculum sources, and appropriate management strategies is ongoing. For now, we recommend continuing to scout fields and managing more common pathogens as necessary.

Fig 3. Three leaves with different levels of disease severity. Photo by Michael Fulcher.

The recent discovery of Alternaria leaf spot in New York is the first recorded incidence of the disease in the United States. We suspect that this disease is more widespread than we currently know. We are cooperating with wheat pathologists in other states to diagnose symptoms they have observed that are similar to those that we have attributed to Alternaria leaf spot in New York. If you encounter symptoms of Alternaria leaf spot, please contact your local field crops extension educator or the Cornell Field Crops Pathology Program.

Acknowledgements:
Funding for this work is provided by USDA-NIFA Hatch grant NYC153436, and the Mycological Society of America through the Emory Simmons Research Award.

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