The photos on this page, taken at Lewis-Brown Horticulture Farm in Corvallis, Oregon, show the symptoms of Winter Brown Blight (Drechslera siccans) on perennial ryegrass. Winter Brown Blight is a member of the genera Drechslera and includes Net Blotch (Drechslera dictyoides) and Melting Out (Drechslera poae). This disease used to be classified as Helminthosporium.
An older variety of perennial ryegrass was planted in early October (foreground in photo above right). The older variety was chosen because of its lack of drought tolerance in order to conduct research in 2011 with Geohumus, a soil additive for water retention. In the background of the above photograph, you can see a block of darker ryegrasses from the new NTEP trial that were planted about the same time. Two pounds of nitrogen (ammonium sulfate) per 1,000 square feet was applied in late November to both areas. The NTEP trial has dark green turf color and the older variety has an off color "lean" look to it. Upon closer inspection, you can see the Winter Brown Blight (photo at left). These photos illustrate a few points related to Winter Brown Blight. First, It is often much worse on new stands of grass. Second, some varieties are much more susceptible than others. Finally, lighter colored varieties tend to be more susceptible than darker colored varieties.
So what will we do about it? There might be a temptation to fertilize again but high nitrogen fertility levels can stimulate Melting Out (Drechslera poae) which can be much more damaging to the turf. The answer: wait until temperatures warm up and then fertilize, if needed.