Wheat Disease Update – April 28, 2025
Categories: Disease updates
Meriem Aoun, Small Grains Pathologist
Department of Entomology & Plant Pathology, Oklahoma State University
In April, wheat streak mosaic (WSM) was observed in Blaine, Kay, Caddo, and Garfield counties. This follows earlier reports of WSM in Garfield and Payne counties from my March update. Samples from these locations were confirmed to be infected with wheat streak mosaic virus (WSMV) by the OSU Plant Disease and Insect Diagnostic Lab.
On April 28, Dr. Brett Carver reported high levels of WSM (Figure 1) at the OSU North Central Research Station in Lahoma. The varieties showing the most severe symptoms in Lahoma were Gallagher, Paradox, and Turret 25. WSMV is transmitted by the wheat curl mite, which oversummers on volunteer wheat and grassy weeds. Destroying volunteer wheat and grassy weeds at least two weeks prior to planting is effective in managing this disease.
Figure 1. Wheat streak mosaic symptoms (OSU North Central Research Station in Lahoma, photo credit: Dr. Brett Carver, 28 April 2025).
The rainfall during the second half of April favored the development of tan spot and septoria tritici blotch on lower leaves. Tan spot (Figures 2 and 3) was observed in a wheat field in Blaine County and Septoria tritici blotch (Figure 4) was observed at the OSU research stations in Stillwater (Payne County) and Chickasha (Grady County). Septoria tritici blotch and tan spot are fungal diseases of wheat that become more prevalent with the adoption of no-till or reduced-till practices that leave wheat residue on the soil surface. To help manage these diseases, growers are encouraged to avoid planting varieties that are highly susceptible.
Figure 2. Tan spot lesions on wheat leaves collected in a grower’s field at Blaine County (23 April 2025).
Figure 3. Dark reproductive structures on wheat stems produced by the tan spot fungus (Blaine County, 23 April 2025).
Figure 4. Lesions of septoria tritici blotch on lower leaves (Stillwater, OK; 23 April 2025).
Lastly, on 21 April, trace levels of stripe rust were observed in Walters (Cotton Country) in Southwest Oklahoma. To date, there have been no observations of leaf rust in Oklahoma this season.