UNL CropWatch April 29, 2011: Wheat Disease Update

UNL CropWatch April 29, 2011: Wheat Disease Update

Healthy wheat field

 

Figure 1. A section of a disease-free wheat field in Jefferson County on April 27.
 

April 29, 2011

A survey of wheat fields this week in southeast Nebraska (Gage, Jefferson, Lancaster, Saline, and Saunders counties) revealed disease levels ranging from none (Figure 1) to low. Wheat in all fields surveyed was in the early stage of jointing.

 Powdery mildew in wheat

Figure 2. Powdery mildew in early stages of development in the lower canopy at Mead on April 28.

Barley yellow dwarf in wheat

 

Figure 3. Barley yellow dwarf at Mead on April 28.

Leaf spotting of wheat

 

Figure 4. Leaf spotting of unknown cause at Mead on April 28.

 Tan spot

Figure 5. Tan spot on a wheat sample from Perkins County submitted to the Plant and Pest Diagnostic Clinic on April 28.

Low levels of disease were found in research plots at Mead in Saunders County. The diseases found were powdery mildew in early stages of development in lower canopy (Figure 2) and barley yellow dwarf (Figure 3). A leaf spotting of unknown cause (Figure 4) also was observed. A sample submitted to the Plant and Pest Diagnostic Clinic from Perkins County showed spotting and yellowing of lower leaves caused by tan spot (Figure 5).

Rainfall over the last two weeks has resulted in conditions (free moisture and high relative humidity) favorable for disease development. Irrigated fields are at a higher risk of disease development, especially if they were irrigated before the rain. The diseases to look for at this time when scouting are powdery mildew and leaf spots such as tan spot and Septoria tritici blotch. These fungal diseases can be managed by applying a fungicide to protect the flag leaf.

Rust diseases start showing up about this time (stripe rust), mid-May (leaf rust) and June (stem rust). These diseases overwinter in southern states and their spores are blown north during the spring and summer. This year, however, dry conditions in the southern states considerably slowed rust development. Therefore, stripe rust is not expected to develop to damaging levels if it develops at all. Some leaf rust overwintered in Kansas. Therefore, it may develop in Nebraska, depending on the weather (favored by wet weather) and how much inoculum (spores) results from Kansas infections. Rust diseases can be controlled effectively by applying a fungicide to protect the flag leaf.

Development of Fusarium head blight (scab) will depend on the weather in May. If we have a wet May, the risk of Fusarium head blight will be high. Applying an appropriate fungicide at early flowering can help reduce losses from scab.

Updated wheat fungicide information prepared by the NCERA-184 multi-state committee of small grains researchers is presented in Table 1.

Barley yellow dwarf and other virus diseases cannot be controlled once they occur.

Stephen Wegulo
Extension Plant Pathologist, Lincoln