Update on the risk for wheat stripe rust
The Kansas wheat crop is progressing rapidly through the jointing stages of development in much of the state. Wheat in the southeast portion of the state is at or fast approaching flag leaf emergence. The crop is generally considered to be two or three weeks ahead of schedule.
Scouting reports indicate that stripe rust has become established in the 2016 wheat crop. This past week, stripe rust was reported in many counties in central and eastern Kansas (Figure 1).
The disease is still at low levels in most fields with a few exceptions in southeast Kansas. This early establishment of stripe rust increases the risk of severe yield loss and growers should continue to monitor the situation carefully. If weather conditions become favorable, the disease could spread rapidly from the lower leaves, where is now established, to the upper leaves critical for grain development.
Growers should check their fields for stripe rust as the crop approaches flag leaf emergence and heading. Fields with stripe rust still in the lower canopy at heading are at a moderate risk for severe yield loss. This means that fungicide applications are likely to result in a profitable yield response (>4 bu/acre) 50-60% of the time. A field is at high risk for severe yield loss if the disease is established on the upper leaves prior to heading. Fungicide applications are likely to result in a profitable yield response 60-90% of the time under these conditions. Variability in fungicide response can primarily be attributed to differences in local weather conditions and susceptibility of the wheat variety.
Growers in most areas of the state have some time to gather more information about the status of disease and costs of fungicide application before making the decision to spray. Fields with good yield potential may benefit from a fungicide application if the disease continues to spread.
More information about making fungicide decisions in wheat can be found in the K-State Research and Extension publication, Evaluating the Need for Fungicide Applications in Wheat, at: http://www.bookstore.ksre.ksu.edu/pubs/MF3057.pdf
Erick De Wolf, Extension Plant Pathology
Romulo Lollato, Wheat and Forages Specialist