Playing off of John's previous post about knowing his Lucky Charms, I thought it would be great to highlight some differences between leaf spots and Microdochium patch. We have seen a lot Microdochium patch throughout Wisconsin. Most likely because the weather has been cool and wet. Before we talk about John's Lucky Charms comment, I think we better discuss the symptoms we have seen.
This time of year Microdochium patch symptoms on creeping bentgrass/annual bluegrass swards are typically water-soaked in the center of the patch with the perimeter of the patch exhibiting chlorosis. Patches this time of year typically range from 3 to 12 inches in diameter. The former name of this disease was pink snow mold. This was a bad name because snow is not required for disease development and the patches are not always pink. This is evident in the picture in the upper left corner of this post. The picture demonstrates the water-soaking in the center of the patch surrounded by chlorotic plants. You'll also notice the abundance of mycelium on the leaves, this is typical of Microdochium patch after incubation. Mycelium production can also occur in the field
Microscopic examination of the leaves coated in mycelium will reveal the crescent moon shaped spores. The spores have a prominent middle septation and lack a foot cell typical of Fusarium species. The second picture in this post represents typical Microdochium nivale spores. John, I loved your analogy of Lucky Charms for describing Microdochium spores. After Damon Smith mentioned the analogy to me, I used it to explain Microdochium to my graduate student. The one problem, he's from China and doesn't know what Lucky Charms are!
We also had a few leaf spot samples come through the clinic. We did not have red leaf spot, but the symptoms are fairly different from Microdochium patch. These symptoms are somewhat similar to what John described, irregular patches that have a reddish, brown tint. The samples that came through our clinic were induced by Bipolairs sorokinana most likely. The transition from last week to this week was fairly dramatic. The previous week was warm and this week the temperatures plummeted. Tonight there is a Freeze/Frost warning for Northern Wisconsin and the Upper Peninsula of Michigan. So we quickly transitioned from summer to fall!
The spores of leaf spot fungi are quite different. The spores are humongous compared to Microdochium spores, have a brown tint and have 6 to 10 septations.
Many golf course superintendents are making a fall application of vincozolin and chlorothalonil or iprodione and chlorothalonil to clean up any late season dollar spot and outbreaks of Microdochium patch. These are good combos for Microdochium and should provide good control until snow mold applications are made. Thiophanate-methyl is fairly effective against Microdochium as well.