A survey of wheat fields in south central and southeast Nebraska on April 27 revealed widespread occurrence of stripe rust in the southernmost tier of counties. Prevalence (percentage of fields with stripe rust) was greater than 70%. Incidence (percentage of plants with stripe rust in a field) ranged from about 15% to greater than 80% in some fields. Severity (percentage of leaf area affected on a plant) was mostly trace to low (less than 10%), although a few isolated leaves had greater than 50% severity.
Growth stage was mostly Feekes 6 (first node detectable); in a few fields it was Feekes 6 to 8 (flag leaf just visible), and in two irrigated fields wheat was in the boot stage. These two irrigated fields apparently had been sprayed and there was no stripe rust in them, but there were some leaves on which stripe rust development had been stopped by the fungicide spray. There was severe winter kill in some fields in south central Nebraska to the extent that the wheat was sprayed with herbicide and another crop will be planted.
A survey of wheat fields in the southern and northern Panhandle and in southwest and west central Nebraska April 23-24 found no foliar diseases, but in the northern Panhandle there was root rot in one field that also had some winter kill. In the west central part of the state, there was severe winter kill in some fields. Growth stage ranged from Feekes 5 (pseudostem erection) in the Panhandle to Feekes 5 to 6 in the southwest and west central parts of the state.
Stripe Rust Management
Fungicides are very effective in controlling stripe rust and other foliar fungal diseases of wheat. It is recommended that fields be scouted regularly for early detection of stripe rust and other diseases such as Septoria tritici blotch, tan spot, and powdery mildew.
Be prepared to spray a fungicide if you see stripe rust in your field. The decision to spray will depend on the:
- level of disease,
- weather conditions (moisture, cool temperatures, and wind favor stripe rust development and spread), and
- susceptibility of the wheat variety to stripe rust.
Because the stripe rust fungus can develop new races, varieties that are known to have good resistance can become susceptible if a new race emerges.
The best timing of a fungicide application to control foliar fungal diseases of wheat is when the flag leaf has emerged. Flag leaf timing is aimed at protecting the flag leaf because, compared to the other leaves, it contributes the most to grain fill. However, depending on how severe stripe rust is, an earlier application may be warranted.
Take into account the yield potential and the price of wheat. If the yield potential is low, consider applying a cheaper fungicide product such as a generic. A list of fungicides and their efficacy ratings on various wheat diseases is provided in a table developed by the multistate north central region committee NCERA-184: Management of Small Grain Diseases.