Update on stripe rust and leaf rust in wheat - Late May 2019
Wheat in many areas of central Kansas is rapidly moving from the flowering to early stages of grain fill. In south central Kansas, the crop is at the watery ripe – early milk stages of kernel development. As we move west in the state, the crop is at various stages of heading and flowering, with the far northwest portions of the state still in the boot stage.
The distribution of stripe rust and leaf rust continues to expand with low levels of disease reported this week in north central and northwest Kansas (Figure 1). In the south central region, where the disease has been active for nearly a month, the severity of stripe rust and leaf rust is highly variable. Severe stripe rust was observed on susceptible varieties (Everest, LCS Mint) in Barber, Kingman, and Sedgwick counties. Although still present and active on varieties that were historically resistant (Larry, Zenda, SY Monument, LCS Chrome), stripe rust has not progressed as rapidly and severity remains low.
Figure 1. Distribution of wheat stripe rust (upper map) and leaf rust (lower map) in Kansas as of May 24, 2019. Maps created by Erick DeWolf, K-State Research and Extension.
Leaf rust remained at low to moderate levels in most fields and research plots that were visited this week. The most severe leaf rust occurred in Cowley county, where susceptible varieties had flag leaf severities approaching 70% at the watery ripe - early milk stages of development.
Low levels of Fusarium head blight (head scab) were observed in research plots in some areas of the south central region this week. There was also evidence of additional infections that where just beginning to express symptoms. The symptoms of fusarium head blight are most evident 21-28 days after flowering. This means that infections of this disease should become visible in southeast and south central Kansas over the next 7-10 days. Fusarium causes large tan lesions on the wheat heads with entire spikelets or potions of the head affected (Figure 2).
Figure 2. Wheat with symptoms of Fusarium head blight. Photo by Erick DeWolf, Research and Extension.
Erick De Wolf, Extension Plant Pathology