The wheat crop in central Kansas is now moving through the flag leaf emergence and flowering stages of growth. The crop is most advanced in the southeast and south central region where many fields are either flowering or already into the early stages of grain development. Wheat in the north central and northwestern regions generally ranges from late-jointing to flag leaf emergence. These growth stages are critical for many wheat diseases and management decisions.
Despite rain delays in field scouting, this week brought more reports of leaf rust and stripe rust activity with both diseases reported in additional counties (Figure 1). The diseases are still primarily at low to moderate levels in the mid-canopy. However, there a few reports of stripe rust moving to the upper leaves. These reports came from Reno and Pratt counties, where were among the first counties to report stripe rust activity this spring.
Figure 1. Summary of scouting reports for rust activity as of May 10, 2019. Maps created by Erick DeWolf, K-State Research and Extension.
There are also indications that genetic resistance of some important wheat varieties is not as effective this season. Preliminary reports indicate the SY Monument, Larry, LCS Chrome and AG Icon varieties are all showing signs of greater susceptibility this year. WB Grainfield, which had an intermediate reaction to stripe rust last year, also appears to developing more disease than expected this year.
The weather was very conducive for the development of stripe rust and leaf rust over the past two weeks. Many regions of the state have experienced frequent rainfall and extended periods of high relative humidity that favor disease development. In fact, many areas of Kansas have experienced more than 100 hours of rust-favorable weather during the first ten days of May (Figure 2).
Figure 2. Duration of weather conditions favorable for the development of rust diseases in wheat. This map shows the number of hours that RH was greater than 85%.
Given these developments, it is important that growers continue to scout fields for signs of disease. Fields with stripe rust or leaf rust established on the upper leaves during the heading or flowering stages of growth are at a high risk for yield loss. Fields with low levels of disease in the mid- or lower canopy are at a moderate risk.
K-State Research and Extension has multiple publications to help growers identify disease, evaluate the need for fungicides, and select the appropriate fungicide products.
“Identifying Rust Diseases of Wheat”:
“Evaluating the Need for Foliar Fungicides in Wheat”:
“Foliar Fungicide Efficacy for Wheat Disease Management”:
Erick De Wolf, Extension Plant Pathology