A survey of wheat fields in southeast, south central, and southwest Nebraska May 27-28 showed severe levels of stripe rust. Many fields with stripe rust showed varying intensities of yellow when viewed from a distance. In some fields, 100 percent of all foliage was yellow and covered with stripe rust pustules, with only the stems and heads retaining green color. In some fields stripe rust had advanced to the stage where teleospores (black spores that form in later stages of rust development) were forming on the leaves.
Many of the fields with severe stripe rust were not sprayed with fungicide to prevent or control the disease or in isolated cases were sprayed too late. Further west and north, stripe rust was not as severe as in the southeast or south central, but its development was picking up speed. Fields that were sprayed had little or no rust.
The overall estimated yield loss due to stripe rust will not be known until later in the growing season. However, in the severely affected fields surveyed on May 27-May 28, 40 percent to 50 percent yield loss is expected. In some fields where the flag leaves were severely diseased before the beginning of grain fill, higher losses are expected.
Weather conditions continue to favor stripe rust development and spread. It is too late to treat stripe rust in fields that are severely affected and especially if flag leaves have more than 50 percent disease severity. In wheat-growing areas further north where stripe rust is not as severe as in the southern part of the state, a fungicide spray is recommended to protect the flag leaf.
If wheat is at the full heading to the flowering growth stage, it is recommended to spray Prosaro or Caramba to both control stripe rust and suppress Fusarium head blight. A list of fungicides and their efficacies on wheat diseases is provided in a table developed by the North Central Regional Committee on Management of Small Grain Diseases (NCERA-184).
Stephen Wegulo is a plant pathologist in Lincoln, Tony Adesemoye is a plant pathologist at the West Central Research and Education Center and Robert Klein is a western Nebraska crops specialist, all with Nebraska Extension.