Time to start scouting wheat for stripe and leaf rust
There were a few more reports of stripe rust from Oklahoma this week and a twitter report of the disease in southeast Kansas bordering Missouri. Several colleagues made visits to research sites in south central Texas and reported severe leaf rust on varieties known to be susceptible to that disease. To date, extension agents, crop consultants and growers all indicate that rust is not widely active in Kansas.
Figure 1. Adult wheat leaves with symptoms of stripe rust. Notice the characteristic rectangular shaped lesions containing yellowish-orange reproductive structures of the fungus. Photo by Erick DeWolf, K-State Research and Extension.
With the wheat crop in south central and southeast Kansas approaching or already at the flag leaf emergence stages of growth, growers are encouraged to be on the lookout for diseases. When people think of stripe rust, they often visualize the characteristic bright yellowish-orange lesions on adult plants (Figure 1). Symptoms of stripe rust on younger leaves are often less rectangular because the fungal growth within the plant is not limited by the veins of younger leaves (Figure 2).
Figure 2. Symptoms of stripe rust on wheat plants that are still at the tillering or jointing stages of growth. Note that the yellowish-orange reproduction of the fungus is more clustered and less rectangular than symptoms on adult leaves. Photos by Erick DeWolf, K-State Research and Extension.
When scouting wheat, it is important to look down within middle layers of the crop canopy for symptoms of disease. Wheat puts out new leaves rapidly during the vegetative growth prior to heading. In some cases, plants may add a new leaf every 7-10 days. These new leaves at the top of the canopy are less likely to express disease symptoms simply because it takes time (10-14 days) for the disease to develop. Focus on leaves that where present over the last 2 weeks. These leaves have a higher probability of infection than the new leaves at the top of the canopy.
More in-field observations will be happening over the next week. Stay tuned for additional detailed reports on the wheat disease status soon.
Erick DeWolf, Plant Pathologist