Wheat Disease Update - UNL CropWatch, May 13, 2011

Wheat Disease Update - UNL CropWatch, May 13, 2011

 Powdery mildew of wheat  Powdery mildew of wheat  Septoria leaf spot of wheat  Tan spot of wheat Barley yellow dwarf of wheat
 Figure 1. Powdery mildew on stems in the lower canopy in research plots at Mead, Saunders County on May 11. Figure 2. Powdery mildew on leaves in the mid canopy in research plots at Mead, Saunders County     May 11.  Figure 3. Septoria tritici blotch on upper leaves in research plots at Mead, Saunders County on May 11.  Figure 4. Tan spot on upper leaves in a grower's field in Webster County on May 12.  Figure 5. Barley yellow dwarf in research plots at Mead, Saunders County on May 11.

May 13, 2011

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A survey of wheat fields this week in southeast and south central Nebraska showed fungal diseases were continuing to develop. Growth stage ranged from Feekes 7 (second node detectable) to Feekes 10 (boots just swollen).

Yellow wheat stands likely due to nutrient deficiency

Figure 6. Yellowing and thin stands due to nutrient deficiency and winter kill, respectively, in a grower's field in Nuckolls County on May 12.

Yellow wheat likely due to nutrient loss

Figure 7. Wheat leaves showing symptoms of nutrient deficiency in a grower's field in Nuckolls County on May 12.

Powdery mildew was evident, especially in fields with a thick stand, in the lower canopy on stems (Figure 1) and leaves. Some leaves had over 40% of the surface covered (Figure 2). Leaf spot diseases were also progressing. Notable among these were Septoria tritici blotch (Figure 3) and tan spot (Figure 4). Barley yellow dwarf (Figure 5) was observed at low levels in several fields.

Yellowing and areas of thin stands of stunted wheat (Figures 6 and 7) were observed in some fields. The yellowing is most likely due to nutrient deficiency. Root and crown rot diseases that start in the fall predispose wheat plants to winter kill, resulting in thin stands in field areas.

No rust diseases were observed.

We recommend that producers continue to scout fields for diseases. If powdery mildew and leaf spot diseases move to the upper leaves and get close to the flag leaf and rain is forecast, consider applying a fungicide to protect the flag leaf.

For the wheat that is already in boot with low disease levels, a fungicide application should be delayed and timed to occur at early flowering to both suppress Fusarium head blight (scab) and control foliar diseases. This will avoid two fungicide applications should wet weather favor development of scab. Monitor the weather and check the risk of scab at the national Fusarium Head Blight Risk Assessment Tool as flowering approaches in the wheat crop. A list of wheat fungicides and their efficacy on various wheat diseases is also available.

Little can be done about barley yellow dwarf and thin stands at this time. The low level of barley yellow dwarf observed will have very minimal or no impact on yield. Root and crown rot diseases are best managed by planting certified, fungicide-treated seed into a firm, well drained seedbed.

Stephen Wegulo
Extension Plant Pathologist, Lincoln.
Jennifer Rees
Extension Educator, Clay County
Dewey Lienemann
Extension Educator, Webster County

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