Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
As you scout your fields at this time of year it is often easy to find scattered brown spots in barley. Sometimes in wheat and rarely in barley, a minor disease called Ascocyta leafspot can be found on winter damaged tissue that can resemble Septoria leafspot but the plants grow out of it once warm weather arrives. The other brown spot that can be seen now is the early symptoms of net blotch. This is a very common leafspot of barley in our region. Severity is determined by the weather (it likes cool and wet) and the susceptibility of the variety. High nitrogen fertilization early will also favor development. Spot blotch rarely gets severe enough here to warrant fungicide applications. The symptoms that develop on barley can vary depending on the variety of the fungus present (there are several forms or isolates of this fungus) and the barley genetics. Later in the season we see the spot blotch form of net blotch (two leaves on the left) more frequently than the classic net blotch symptom seen on the two leaves on the right in the picture below.
Two leaves on left- spot blotch form of net blotch, on the right classic net blotch symptoms
Sometimes the only symptom development is a small brown spot or fleck that never enlarges or blights a leaf. This is thought to be the barley resistant reaction to the fungus infection.
The picture above, taken two days ago, shows the early symptoms on leaves before jointing has occurred. Typically, as the season warms the older infected leaves at the base of the plants will die and the new leaves may or may not develop more symptoms depending on the weather.