Growth of the wheat crop in Nebraska is advancing and will continue to do so as temperatures warm up. During field surveys conducted during the week of April 21 in the southeast, southwest, and southern Panhandle, the majority of fields looked healthy with a luxuriant green canopy (Figure 1), but the soil looked dry, indicating the need for moisture to sustain development of the wheat crop.
Growth stage ranged from Feekes 4 (stem elongation) to Feekes 6 (first node palpable) in most of the fields surveyed. Growth stage in some fields in Hitchcock County was Feekes 7 (second node palpable and next to last leaf visible).
Isolated cases of the wheat streak mosaic virus (WSMV) disease complex (Figures 2 and 3) were observed in Gage County in the southeast and Hitchcock County in the southwest. Some fields had trace to low levels of fungal leaf spot diseases (Septoria tritici blotch and tan spot; Figure 4). No rust diseases were found.
Management
Detection of symptoms of the WSMV disease complex and fungal leaf spots indicates that it is time to scout Nebraska wheat fields for disease detection.
Foliar fungal diseases are favored by moisture from rainfall or irrigation and high humidity. They are managed by planting resistant varieties and applying a fungicide to protect the flag leaf.
Table I, prepared by the North Central Regional Committee on Management of Small Grain Diseases (NCERA-184) and presented by the Crop Protection Network, lists fungicides registered for use on wheat and their efficacies in controlling the various fungal diseases that occur on wheat.
Additional management strategies for fungal leaf spots are crop rotation and residue management. The fungi that cause these diseases survive and overwinter on crop residue.
The WSMV disease complex is caused by three viruses that may occur singly, doubly, or in triplicate. All three viruses are transmitted by wheat curl mites. Symptoms and yield loss are more severe in double and triple infections, and complete loss of the wheat crop is not uncommon.
To manage the WSMV disease complex, control volunteer wheat, especially volunteer that emerges following a hailstorm when wheat is mature enough for the shattered grain to germinate. All other volunteer, including that in summer crops such as sunflower, corn and millet, should be controlled. Volunteer should be completely dead at least 14 days before planting wheat in the fall.
Other management strategies for the WSMV disease complex include planting resistant or tolerant varieties, avoiding early planting, and avoiding planting wheat next to late maturing crops that are hosts to the mites or viruses, such as corn, millet and sorghum.
