By Stephen Wegulo
Extension Plant Pathologist
Severity of wheat diseases has increased significantly over the last week. At UNL's Agricultural Research and Development Center (ARDC) near Mead, leaf rust (Figure 1) was found on May 19 for the first time in Nebraska this growing season. Incidence (percentage of plants diseased) was trace and severity (percentage of leaf area covered with pustules) was about 2%. It was mainly on lower leaves in research plots planted with a susceptible cultivar. Stripe rust was widespread in research plots. Barley yellow dwarf (Figure 2), a virus disease, was also found at low levels in a wheat field at the ARDC on May 19.
Figure 1. Leaf rust on a lower leaf in a research plot at the UNL ARDC near Mead on May 19.
Figure 2. Barley yellow dwarf in a wheat field at the UNL ARDC near Mead on May 19.
Figure 3. Severe stripe rust on a susceptible breeder line at the UNL Havelock Farm on May 21.
In a breeder nursery at UNL's Havelock Farm in Lincoln on May 21, incidence of stripe rust was 100% and severity was over 70% on many leaves in plots of susceptible lines (Figure 3). Highly resistant lines had no stripe rust (Figure 4). Other diseases observed at low levels at Havelock Farm were barley yellow dwarf, powdery mildew, and bacterial streak (Figure 5).
Figure 4. A breeder line highly resistant to stripe rust side by side with a susceptible line at the UNL Havelock Farm on May 21.
Figure 5. Bacterial streak on a breeder line at the UNL Havelock Farm on May 21.
Severity of leaf spot diseases (Septoria tritici blotch and tan spot) at the ARDC and Havelock Farm had also increased compared to the previous week.
Management
Weather conditions continue to favor development of stripe rust and other foliar diseases of wheat. A fungicide spray to protect the flag leaf is recommended. If wheat is at full heading or early flowering, consider applying Prosaro or Caramba to both control foliar diseases and suppress Fusarium head blight. The factors to consider when making a decision to apply a fungicide are outlined in this CropWatch article.
Observe label instructions and restrictions when applying any fungicide. 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).
Bacterial streak and barley yellow dwarf cannot be controlled once they occur.
Source: unl.edu