Wheat Disease Update – 10 May 2023
Meriem Aoun, Small Grains Pathologist
Department of Entomology & Plant Pathology, Oklahoma State University
Root rots were the primary diseases observed this week (May 8-9) in wheat fields and research trials in Cherokee (Alfalfa County), Alva (Woods County), and Lahoma (Garfield County). Infected plants were stunted, white, with discolored roots and stems. Peeling leaf sheaths in the lower stem internodes showed brown and pinkish discolorations on infected plants. Pink discoloration indicates infections by Fusarium species (Figure 1). Infected plants with root rot died prematurely and produced white heads that were either sterile or filled with shriveled seed.
Fusarium root rot was also severe in a research trial in Lahoma. In this experiment most varieties planted on October 30, 2022 showed higher root rot incidence and severity compared to plots planted on December 5, 2022. This shows that delayed planting can help reduce the severity of root rots (Figure 2).
Loose smut was observed in several fields in Alva, Cherokee, Lahoma, Chickasha (Grady County) and Stillwater (Payne County) (Figure 3). Freeze damaged wheat heads were also seen in Alva and Cherokee as shown in Figure 4.
Leaf spotting diseases were observed in low to moderate incidence/severity mainly on the lower leaves in Alva, Cherokee, Lahoma, and Stillwater (Figure 5). Moisture during the last week of April and early May favored the appearance of these fungal foliar diseases.
This week (May 3 – 9), spot blotch (caused by Bipolaris sorokiniana, which also causes common root rot, Figure 6) was observed in low incidence and severity in Stillwater, Lahoma, and Alva. In my previous update, I also reported low incidence/severity of spot blotch in Chickasha, OK on April 28.
On May 4, a few stripe rust lesions were observed in the OSU Entomology and Plant Pathology farm in Stillwater (Figure 7). From my previous update, stripe rust was also reported in Chickasha, OK on April 21. On May 10, Brian Olson (OSU Wheat Pathology Lab Technician) reported a trace level of leaf rust (on a single leaf) in a wheat research plot at the OSU Agronomy farm in Stillwater, OK.
Wheat Disease Update – 2 May 2023
Meriem Aoun, Small Grains Pathologist
Department of Entomology & Plant Pathology
Oklahoma State University
Wheat tours during the last week of April in southwestern Oklahoma (Tipton, Altus), south-central Oklahoma (Walters), and central Oklahoma (Apache and Chickasha) showed wheat in these areas to be at heading/flowering stages. On April 21, stripe rust was first observed at the OSU South Central Research Station in Chickasha (Grady County), Oklahoma (Figure 1). Natural infection was found on the susceptible wheat variety ‘Pete’ with a disease incidence of ~ 5%. On April 28, the disease incidence on Pete increased to ~ 15% due to cool temperatures and precipitations during the last week of April. Dr. Brett Carver (OSU wheat breeder) also reported a very low incidence of stripe rust in Lahoma (Garfield County).
The rain and cool temperatures during the last week of April favored the appearance of other fungal foliar diseases including Septoria tritici blotch, spot blotch, powdery mildew, and loose smut. On April 28, I observed low incidence of Septoria tritici blotch (Figure 2) in Chickasha mainly on the lower-mid canopy. On April 28, spot blotch (caused by Bipolaris sorokiniana, Figure 3), was present in low incidence and severity in Chickasha (Grady County). Low incidence of spot blotch was also observed in Apache (Caddo County) on April 27 by Mike Schulte (Oklahoma Wheat Commission executive director) and Dr. Amanda Silva (OSU Small Grains Extension Specialist). Bipolaris sorokiniana can also cause common root rot which has been prevalent in 2022-2023 in Western Oklahoma.
On April 28, I also observed a few hotspots of powdery mildew in a research trial in Chickasha on lower leaves. A few heads showed symptoms of loose smut in Chickasha on April 28 (Figure 4). After, the recent precipitations, we recommend continuous scouting for diseases. Although, environmental conditions are conducive for diseases, disease pressure is considered very low currently to consider fungicide applications.