Diseases Observed in an April 5 Survey of Wheat Fields
|Figure 1. On closer examination, this healthy looking field in Jefferson County had areas with virus and Septoria leaf blotch symptoms.|
|Figure 2. Powdery mildew. This disease was observed at high severity levels in research plots in Lancaster County. It was also observed in growers' fields with thick stands.||
Figure 3. Septoria leaf blotch was observed at low levels in most fields surveyed.
|Figure 4. Some field areas had significant levels of virus symptoms.|
April 6, 2012
Figure 5. This field in Webster County had large yellow areas.
|Figure 6. Close-up of leaves in a yellow area in the field shown in Figure 5.|
An April 5 survey of fields in the southern tier of counties from the southeast to the southwest found the wheat crop at various stages of development ranging from jointing to flag leaf emergence. Most fields surveyed looked healthy (Figure 1). However, closer examination revealed low levels of disease in some of the fields. The three categories of diseases most observed were powdery mildew (Figure 2), fungal leaf spot diseases, mainly Septoria leaf blotch (Figure 3), and virus diseases (Figure 4). Rust diseases were not observed.
Some fields with large yellow areas were also observed (Figure 5), confirming recent reports. Close examination of wheat leaves in the yellow area in Figure 5 showed general yellowing indicative of nutrient deficiency (Figure 6). Note that these leaves do not have the mosaic, mottling, or streaking of yellow and green (Figure 4) that is usually associated with virus infection. In one field, there were areas that looked brown from the edge of the field (Figure 7). Close examination of the leaves (Figure 8) revealed that this browning was due to fertilizer burn which is characterized by death of tissue at the leaf tips.
Note: Also see the April 6 Market Journal for an interview by host Jeff Wilkerson with Stephen Wegulo.
|Figure 7. This Webster County field in south central Nebraska had brown areas visible from the edge.||Figure 8. Close-up of a leaf in a brown area in the field shown in Figure 7.|
Dry weather in most parts of the state has kept fungal disease levels low. However, in areas where there has been precipitation and in fields with thick stands, diseases such as powdery mildew, Septoria leaf blotch, and tan spot can develop rapidly. Fields should be scouted routinely for early detection of these diseases and in anticipation of the arrival of leaf and stripe rusts which have been confirmed in Kansas. When scouting, look for disease symptoms above as well as inside the leaf canopy. Foliar fungal diseases can be controlled effectively by timely application of a fungicide aimed at protecting the flag leaf.
Virus diseases, on the other hand, cannot be controlled once they occur. Four virus diseases have been confirmed this year: wheat streak mosaic, Triticum mosaic, soilborne mosaic, and isolated cases of barley yellow dwarf. See the March 30 CropWatch article for virus disease management strategies.
Yellowing due to inadequate nutrients can be alleviated by fertilizing the wheat crop. It is helpful to do a soil test and determine which nutrients are needed most before fertilizing. Fertilizer burn should cause little concern as the wheat crop will grow out of it.
Extension Plant Pathologist