The wheat crop in Kansas is now at the flag leaf emergence stage of growth in much of southern and central Kansas. The crop is at mid- to late-joining in the west central and northwest regions of the state. The crop is generally considered to be two or three weeks ahead of schedule.
Stripe rust continues to be our primary focus with new reports from additional counties and further disease development in central Kansas. The disease is still limited to the lower leaves for the most part with occasional mid canopy leaves with trace levels. The incidence of stripe rust on the lower leaves of susceptible varieties ranges from 1-30%
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.
Leaf rust was observed at multiple locations in central Kanas this week also. As with stripe rust, leaf rust is also on the lower leaves. Only trace levels have been found so far in most plots. We did observe a few fields and plots in Reno and McPherson counties with incidence of leaf rust approaching 90% on the lower leaves. The severity of the infection was still low (<10%) in most cases.
The dry conditions may be slowing the spread of leaf diseases temporarily, but growers should be watching this situation carefully. Be prepared to apply a fungicide if disease continues to progress.
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:
Alicia Boor is the Agriculture and Natural Resources agent for Barton County K-state Research and Extension. One can contact her by email at email@example.com or calling 620-793-1910