Leaf Spot Look-alikes

August 20, 2009 in Extension

Posted by Pete Landschoot

If you’re seeing brown spots and melting-out on your ryegrass of late, keep in mind that there are other late-summer leaf spot diseases of perennial ryegrass besides gray leaf spot.  I recently observed a case in central PA in which a contractor suspected gray leaf spot was taking out his newly-seeded perennial ryegrass.  In fact, the disease turned out to be a different leaf spot disease.  The spores appeared similar to descriptions of Drechslera siccans.  For the record…..I was fooled as well.  I could have sworn it was gray leaf spot when I looked at the turf in the field.  When garden-variety leaf spot diseases get rolling on susceptible hosts during extended periods of high humidity, they can resemble early stage symptoms of grey leaf spot.  Some common leaf spot diseases of perennial ryegrass include net blotch and leaf blight (Pyrenophora dictyoides (sometimes referred to as Drechslera dictyoides); Leaf spot, leaf blight, and foot rot (Drechslera siccans), and leaf blight and crown rot (Drechslera catenaria).   Only your diagnostician….using a microscope…..knows for sure.