Wheat Disease Update

Wheat Disease Update

Photo of Tan Spot
Figure 1. Tan spot
Photo of leaf blotch
Figure 2. Septoria leaf blotch

May 15, 2009

Photo of barley yellow leaf 

Figure 3. (Left) Barley yellow dwarf

Figure 4. (Below) From the road this field looks healthy, but on closer inspection researchers found a 25% incidence of tan spot that was still at a low (2%) severity.

All photos by Stephen Wegulo

Photo of tan spot infested field
Photo of a wheat field with wheat residue
Figures 5 and 6. Wheat field (above) with a significant amount of wheat residue, which was found to have pseudothecia (below). These fungal fruiting structures release the spores of the tan spot fungus in early spring.
Tan spot pseudothecia on wheat residue
A tour of wheat fields on May 13 and 14 revealed low levels of disease. In a grower's field in Saline County on May 13, only tan spot (Figure 1) at trace levels (less than 0.5% incidence = percentage of symptomatic plants) was observed on lower leaves. In Jefferson County on May 13, Septoria leaf blotch (Figure 2) and tan spot were observed at trace levels in a grower's field. This field also had barley yellow dwarf (Figure 3) at approximately 1% incidence.

On May 14 in Lancaster County, an apparently healthy looking field (Figure 4) had approximately 25% incidence of tan spot, but disease severity (percentage of leaf area covered with lesions) was low (about 2%). This field had a significant amount of wheat straw on the soil surface (Figure 5). Close examination of the wheat straw revealed pseudothecia (Figure 6). These are the sexual fruiting structures of the tan spot fungus that release the spores which cause initial infections in early spring.

In research plots at UNL's South Central Agricultural Lab in Clay County on May 14, tan spot and Septoria leaf blotch were observed at trace levels. Incidence of barley yellow dwarf was about 3% in one variety.

Farther west, in Keith County, no leaf spot diseases were observed in an irrigated grower's field near Paxton. There were isolated yellow plants at trace levels of incidence. The yellowing was attributed to soilborne wheat mosaic virus.

Rust in Kansas

Rust diseases have not been observed in Nebraska to-date. However, leaf rust was found in north central Kansas on May 11. Nebraska producers should monitor wheat fields for leaf rust in the next two to three weeks.

Wheat Disease Treatments

Scouting for diseases should continue and fungicide application should be timed to protect the flag leaf. Fungicide application is likely to be profitable if environmental conditions (wet weather and prolonged periods of no sunshine) favor development of damaging levels of disease.

A partial list of foliar fungicides registered for control of wheat diseases can be found in a story in the May 1 issue of CropWatch.

Stephen Wegulo
Extension Plant Pathologist