Wheat Disease Update – 25 March 2024
Meriem Aoun
Department of Entomology & Plant Pathology
Oklahoma State University
On March 19, Tyler Lynch (Agriculturalist Sr, OSU, Department of Plant and Soil Sciences, OSU) brought wheat samples (Figure 1) showing tan spot symptoms from the wheat variety trials at Balko (Beaver County) and Hooker (Texas County), OK. Tyler reported that tan spot incidence was low and mainly observed on lower leaves. Tan spot was reported at Chickasha (Grady County) in my previous update on March 21. On March 14, spot blotch (caused by Bipolaris sorokiniana, Figure 2) was found at low incidence at Chickasha.
Figure 1. Tan spot on lower wheat leaves at Chickasha, OK (March 15, 2024).
Figure 2. Spot blotch on wheat leaves at Chickasha, OK (March 14, 2024).
On March 19, powdery mildew was reported in a grower’s field at Hominy (Osage county), northeastern Oklahoma (Figure 3, 4). The infected field area showed pale green to yellow patches as shown in Figure 3. White cottony patches (fungal mycelium and spores) were observed on the upper surface of lower leaves (Figure 4).
Figure 3. Light green to yellow patches in a wheat field affected by powdery mildew at Hominy, OK (March 19, 2024).
Figure 4. White cottony patches (fungal mycelium and spores) indicative of powdery mildew infection (Hominy, OK; March 19, 2024).
Stripe rust (Figure 5) was observed at Altus, Southwestern OK (Jackson County) on March 20, 2024. On March 22, Tyler Lynch reported moderate to high stripe rust pressure in the wheat variety trial at Altus with susceptible varieties showing up to 70% disease severity. The wheat crop at Altus is at flag leaf stage and all wheat plots at the variety trials showed symptoms of stripe rust. The wheat varieties in Altus were rated for their reactions to stripe rust. On March 22, Tyler also found stripe rust at Tipton (Tillman County), OK, however the disease pressure was low.
Figure 5. Stripe rust on a susceptible winter wheat variety at Altus, OK (Photo: Mike Schulz, March 20, 2024).
Wheat Disease Update – 21 March 2024
Meriem Aoun
Department of Entomology & Plant Pathology
Oklahoma State University
Late February-early March 2024, symptoms of wheat soilborne mosaic virus (SBWMV)/wheat spindle streak mosaic virus (WSSMV) were observed at Oklahoma State University (OSU) Entomology and Plant Pathology farm in Stillwater. The susceptible wheat check ‘Vona’ and other susceptible hard winter wheat breeding lines showed stunting and yellowing (Figure 1, 2). Most wheat varieties grown in Oklahoma and the U.S. Central Plains are resistant to these virus diseases.
Figure 1. Resistant vs. susceptible hard winter wheat lines to wheat soilborne mosaic virus /wheat spindle streak mosaic (Stillwater, OK; February 29, 2024).
Figure 2. Wheat showing reactions to the wheat soil-borne mosaic (WSBM)/wheat spindle streak mosaic (WSSM) complex. Left photo: Symptoms typical of WSBM. Right photo: Symptoms typical of WSSM.
On March 15, 2024, Septoria tritici blotch (Figure 3, 4) was observed in Dr. Amanda Silva’s variety trial at the OSU North Central Research Station in Lahoma, OK (Garfield County). Septoria tritici blotch was observed on all wheat varieties, however symptoms were limited to the lower canopy. On March 15, 2024, we also observed symptoms of tan spot (Figure 5) at the OSU South Central Research Station in Chickasha, OK (Grady County). Tan spot incidence was low to moderate at Chickasha and symptoms were observed on lower leaves.
Figure 3. Wheat showing reaction to Septoria tritici blotch (Lahoma, OK; March 15, 2024).
Figure 4. Septoria tritici blotch on wheat leaf. Black specks on the lesions indicate pycnidia (Lahoma, OK; March 15, 2024).
Figure 5. Symptoms of tan spot on lower wheat leaves (Chickasha, OK; March 15, 2024).
Stripe rust (Figure 6) and leaf rust (Figure 7) have not yet been observed in Oklahoma. However, there were reports of stripe rust in wheat fields in both Louisiana and Texas as early as January 31. On March 7-8, 2024, Dr. Shuyu Liu (Wheat Breeder, Texas A&M University) reported high incidence and severity of stripe rust at McGregor, Chillicothe, and Castroville TX. The early appearance of stripe rust in Texas indicates a potential stripe rust epidemic in Oklahoma if the weather conditions continue to be favorable. Leaf rust was also observed at lower incidence/severity at Castroville, TX on March 8, 2024 and it can develop further with rising temperature.
Figure 6. Stripe rust on a susceptible winter wheat variety in Castroville, TX (Photo: Dr. Shuyu Liu, March 8, 2024).
Figure 7. Leaf rust on a susceptible winter wheat variety in Castroville, TX (Photo: Dr. Shuyu Liu, March 8, 2024).