Wheat disease update: Increased levels of leaf rust
A May 17 visit to a breeder nursery at the UNL Agronomy Farm in Lincoln, Lancaster County, found that leaf rust has increased from low levels (less than 5 percent severity) a week ago to more than 30 percent of flag leaves covered with pustules in susceptible lines (Figure 1). Stripe rust (Figure 2) was still the predominant foliar disease. Wheat was mostly past the flowering stage and into the dough stage of crop development. The incidence of two or more leaf diseases on the same plant was high. Most notable were complexes of stripe rust and leaf rust (Figure 3) and Septoria leaf blotch and rust (Figure 4). Head diseases/disorders were also observed at trace to low levels including Fusarium head blight (Figure 5), loose smut (Figure 6), and frost damage (Figure 7).
Dry conditions and warmer temperatures have slowed down stripe rust development. However, temperatures are currently suitable for leaf rust, but lack of moisture has slowed down its development and spread in rain-fed fields. Most wheat fields in south central and southeast Nebraska are past the crop development stage at which foliar fungicides can be applied. Damage due to leaf rust will be less than it would have been in a more average year because the wheat crop in this region is at least two weeks ahead of normal crop development.
Although trace levels of Fusarium head blight can be found in fields in south central and southeast Nebraska, the risk for development of damaging levels of the disease remains low due to limited moisture. Loose smut (Figure 6) occurs to some extent every year and its incidence is usually higher in fields that were planted with bin-run seed or seed that was not treated with a fungicide. To limit yield loss due to loose smut, use certified, fungicide-treated seed when planting in the fall.
Currently, the most prevalent virus diseases in wheat are barley yellow dwarf and wheat streak mosaic.