Figure 1. Leaf rust on a wheat leaf from Nuckolls County, April 26.  (Source: Ken Herz)		Figure 2. A patch of yellow wheat in a field in Webster County north of Cowles on April 27.

April 30, 2010

As of April 28, wheat diseases in Nebraska were at very low levels. Current weather conditions (wet weather and overcast skies) are favorable to development of several diseases including leaf spots, powdery mildew, and leaf and stripe rusts. Leaf rust and stripe rust have been reported in the southern states and most recently in Kansas. Stripe rust has been found in central and northeastern Kansas, with the most recent finds in Ellis and Riley counties.

On April 29, stripe rust was confirmed on a sample from Johnson County in southeast Nebraska. On April 26, leaf rust (Figure 1) was found in Nuckolls County, Nebraska. This is one of the earliest dates leaf rust has been found in Nebraska in recent years. Leaf rust is usually first seen in the growing season after the first week of May, most often around mid-May. Stripe rust is more damaging than leaf rust. This year it has been reported on varieties that previously were resistant, indicating that there may be a new race of the stripe rust fungus.

Major stripe rust epidemics have not occurred in Nebraska since 2005. However, given the unusually high levels of stripe rust reported in the southern states and the cool, wet weather we are experiencing, the risk of stripe rust development in the state is high. Growers are encouraged to routinely scout their fields for leaf rust and stripe rust and to be prepared to apply an appropriate fungicide to prevent damaging levels of these and other foliar diseases. Fungicide applications should be timed to protect the flag leaf.

A sample from Nuckolls County submitted to the UNL Plant and Pest Diagnostic Clinic the week of April 19 showed symptoms of tan spot. Leaf spots such as tan spot and Septoria leaf blotch are starting to appear on the lower leaves, especially in no-till fields with wheat stubble on the ground. A sample submitted to the Diagnostic Clinic on April 26 from Lancaster County was suspected to have soilborne mosaic virus. Several fields in south central Nebraska have large patches of yellow wheat (Figure 2). The cause of the yellowing is not known at this time. Moderate levels of powdery mildew (Figure 3) and leaf spots (tan spot, Septoria leaf blotch, Figure 4) also were observed in wheat fields in south central Nebraska.

Stephen Wegulo
Extension Plant Pathologist, Lincoln
Dewey Lienemann
Extension Educator, Webster County