Wheat Disease Update – 19 May 2022
Meriem Aoun, Small Grains Pathologist
Department of Entomology & Plant Pathology, Oklahoma State University.
During my visit to wheat fields in Morris (Okmulgee County) on May 16, I observed multiple fungal and bacterial diseases. Wheat crop in Morris looked good and tall compared to other locations in Oklahoma (Figure 1). Morris got substantial amount of precipitation, which favored some fungal and bacterial diseases.
Figure 1. Winter wheat crop in Morris, Oklahoma was in good condition as of May 16, 2022 (Courtesy Dr. Amanda Silva).
Bacterial streak (on the leaf, Figure 2) and black chaff (on the head, Figure 3) were frequently observed on multiple winter wheat varieties including ‘Big country’ and ‘WB 4401’. Bacterial streak and black chaff are two phases of the same disease and are favored by humid and warm climate, which was the case in Morris.
Figure 2. Symptoms of bacterial streak on the winter wheat variety ‘WB 4401’ in Morris, Oklahoma (Courtesy Dr. Amanda Silva; May 16, 2022).
Figure 3. Symptoms of black chaff on glumes and neck (Morris, Oklahoma; May 16, 2022).
In Morris, I also observed Septoria leaf spot and tan spot in the lower and mid canopy, but nothing much on flag leaves. Septoria leaf spot was more common and found on varieties like ‘Skydance’ and ‘Crescent AX’ (Figure 4). Both diseases were also observed in the Stillwater Agronomy Research Station on OSU winter wheat breeding lines. In addition, spot blotch and powdery mildew were found in multiple experimental plots in Stillwater on susceptible winter wheat varieties and OSU breeding lines (Figure 5).
Figure 4. Septoria leaf spot symptoms on the winter wheat variety ‘Crescent AX’ in Morris, Oklahoma (May 16, 2022).
Figure 5. The black spots show symptoms of spot blotch, whereas the white patches correspond to powdery mildew infection on an OSU winter wheat breeding line (Stillwater, Oklahoma; May 11, 2022).
Powdery mildew and leaf rust were observed in both Stillwater and Morris (Figure 6 and 7). As I previously reported powdery mildew was observed in multiple locations in Oklahoma since April whereas leaf rust was first observed this year in Oklahoma during the second week of May.
Figure 6. Leaf rust symptoms on the hard red winter wheat variety ‘Baker’s Ann’ (Morris, Oklahoma; May 16, 2022).
Figure 7. Symptoms of leaf rust (circular orange pustules) and powdery mildew (white patches) on the hard red winter wheat variety ‘Baker’s Ann’ (Morris, Oklahoma; May 16, 2022).
In addition to these foliar diseases, I observed some head diseases including sooty mold (black head mold) (Figure 7) in wheat fields in Morris, El Reno, and Stillwater. Humid conditions promote this disease on wheat heads. Often wheat that has been subjected to a stress such as freeze, root rot, or drought shows a greater severity of sooty mold than healthy wheat. I also observed loose smut (Figure 8) in Chickasha, Stillwater, and Morris.
Figure 8. Symptoms of sooty mold on winter wheat in Morris, Oklahoma (May 16, 2022).
Figure 9. Symptoms of loose smut on the winter wheat variety ‘WB 2158’ (May 3, 2022).
Wheat Disease Update – 12 May 2022
Meriem Aoun, Small Grains Pathologist
Department of Entomology & Plant Pathology Oklahoma State University
Root/crown/foot rots were observed in multiple wheat fields in April and May in Woods, Alfalfa, Blaine, Cotton, and Payne counties. Dr. Amanda Silva reported severely damaged wheat plants in drought stressed fields mainly in Cherokee and Alva (Figure 1). Infected plants were stunted and white and had poor root systems. Although the plants were drought stressed throughout the growing season, much of the damage was not noticeable until after wheat heading. Dr. Silva observed pinkish discoloration on infected plants in Cherokee after peeling the leaf sheath in the lower stem internodes, which indicates that the infection was caused by Fusarium (Figure 2).
Figure 1. White, stunted, and drought-stressed plants showing symptoms of root/crown/foot rots (Cherokee, Oklahoma; photo credit: Dr. Amanda Silva; May 12, 2022).
Figure 2. Pink discoloration indicates that root/crown/foot rot was caused by Fusarium (Cherokee, Oklahoma; photo credit: Dr. Amanda Silva; May 12, 2022).
The rain in early May in some locations in Oklahoma provided suitable environmental conditions for the appearance of some fungal diseases including rusts. This week, stripe rust was observed in the Stillwater Agronomy Research Station on susceptible wheat varieties like ‘Pete’ and some OSU breeding lines (Figure 3). Leaf rust was found on the susceptible wheat variety ‘OK Bullet” and on some OSU breeding lines (Figure 4). Rust diseases have not been found in other locations in Oklahoma. The current pressure is low and late compared to the previous year due to drought conditions through the growing season. However, rust disease incidence can increase in coming weeks if weather conditions are favorable.
Figure 3. Stripe rust on a susceptible OSU winter wheat breeding line in the Stillwater Agronomy Research Station, Oklahoma (the photo was taken on May 10, 2022).
Figure 4. Initial leaf rust pathogen infection on a winter wheat OSU breeding line in the Stillwater Agronomy Research Station, Oklahoma (the photo was taken on May 10, 2022).