The wheat in south central Kansas is currently into the early stages of grain development but the kernels are not yet watery ripe. Stripe rust was severe at many locations this past week, with incidence near 100% and severity ranging from 20-80% depending on the variety. Severe disease pressure during the early stages of grain development will likely have a significant impact on grain yield. Fields with severe damage to the flag leaves may experience more than 20% yield loss.
Varieties with the most stripe rust included Armour, Everest, Garrison, LCS Wizard, Ruby Lee, TAM 111, and WB-Redhawk. Interestingly, varieties with a Jagger pedigree, such as 1863, Danby, Fuller, and WB4458, appeared to be moderately resistant. The varieties Oakley CL, Gallagher, WB-Cedar, and WB-Grainfield also appear resistant or moderately resistant at this time. This pattern of susceptibility among varieties indicates that the stripe rust population is similar to what was present in 2012.
Leaf rust was also present on many of the same locations I visited this week in south central Kansas. In most cases, incidence of leaf rust was around 10-20% with severity less than 1% on the flag leaves. There was more leaf rust at the South Central Experiment Field near Hutchinson than at other locations. At this location, leaf rust severity was approaching 10-15% on the flag leaves of the susceptible variety Overley.
Reports from the central and western regions of the state also indicate that stripe rust has moved to the upper leaves in many fields. There are a few reports of severe disease incidence on the flag leaves in some fields.
Fungicides may be an option for some fields with good yield potential and seed production fields where the value of the grain is greater. Be mindful of the harvest restrictions on the fungicide products, however. Many fungicide products can no longer be applied once the wheat is flowering, while others have a 30-day pre-harvest interval. Take these label restrictions seriously. Failure to follow the label directions can result in quarantines on harvested grain.
Erick De Wolf, Extension Plant Pathology