Wheat Disease Update - CropWatch, May 20, 2011

Wheat Disease Update - CropWatch, May 20, 2011

Flowering wheat Wheat heading out at 1 ft Photo: Wheat - powdery mildew Photo: Loose smut of wheat
Figure 1. A flowering wheat head in a grower's field in Thayer County on May 18. Figure 2. Wheat headed at 1 foot tall in Jefferson County on May 18.  Figure 3. Severe powdery mildew in a breeder nursery at Lincoln, Lancaster County, on May 18.  Figure 4. Loose smut in a grower's field in Jefferson County on May 18.

 
May 20, 2011

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A survey of wheat fields in southeast Nebraska on May 18 found growth stages ranging from boot to full heading, with a few plants in some fields starting to flower (Figure 1). Due to prolonged, cooler than normal temperatures this spring, coupled with lower than normal moisture levels, wheat in some fields was stunting and heading at about 1 foot tall (Figure 2).

Photo: Fungal leaf spots in wheat

Figure 5. Fungal leaf spots on a leaf in the mid canopy in a grower's field in Thayer County on May 18.

Wheat frost injury

(Left) Figure 6. A wheat head showing frost injury in Thayer County on May 18.

Image - Wheat head trapping


Figure 7. Head trapping commonly associated with synthetic auxin herbicide injury in Thayer County on May 18.

Several diseases were observed. Notable among these was barley yellow dwarf, which was present to some level in every field surveyed.

Powdery mildew was also widespread, with severity ranging from trace to more than 65% of leaf surfaces covered in the mid canopy in other fields (Figure 3).

Other diseases observed were loose smut (Figure 4) and fungal leaf spot diseases (Figure 5).

No rust diseases were observed. Leaf rust is still at low levels in central Kansas. However, with the recent rain, sporulation of the leaf rust fungus can increase, raising the probability of spores arriving in Nebraska. Producers should continue to scout fields for rust diseases.

The National Fusarium Head Blight Risk Assessment Tool indicated a low risk in Nebraska as of May 20. This risk is likely to increase within the next week to two weeks if rainfall continues. A fungicide application at early flowering is recommended if the FHB risk level is elevated to high.

Hail damaged wheat

Figure 8. Hail damage in research plots at Mead, Saunders County, from a May 12 storm.

The fungicides that are effective in suppressing fusarium head blight are very good to excellent in controlling powdery mildew, rusts, and fungal leaf spots. If the levels of these diseases are low and the flag leaf and the flag -1 leaves are free of disease, delay a fungicide application until early flowering and then apply a fungicide that will suppress both fusarium head blight and protect the flag leaf from powdery mildew, rusts, and fungal leaf spots.

Abiotic disorders also were observed, including frost injury (Figure 6), head trapping commonly associated with synthetic auxin herbicide injury (Figure 7), and hail damage that occurred in isolated spots in some fields on May 12 (Figure 8).

Stephen Wegulo
Extension Plant Pathologist, Lincoln
Emmanuel Byamukama
Postdoctoral Research Associate, Lincoln