Last week I was touring a golf course with the Superintendent and we had a discussion about yellow spots on one of their putting greens. Yellow spots can be the result of a number of diseases and conditions. Poa annua contamination and yellow tuft were the first two possibilities that came to mind. Being able to correctly identify the problem is very valuable as the fungicides labeled for yellow tuft can be costly.
This particular green is grassed with the new, high-density bentgrass cultivars. Many of the new bentgrasses are genetically darker green compared to the older cultivars. As a result, any poa that is present is even more distinguishable within the canopy. This color difference can easily be misdiagnosed as a disease and could be the cause of the yellow spots.
Like most diseases, yellow tuft seems to be most prevalent in areas that are poorly drained, over-irrigated, or have excessive thatch. This green is rather flat and has relatively poor surface drainage. The weather so far during the month of June has provided plenty of moisture with many parts of the state receiving over 5 inches of rain.
I collected some samples of the affected turf for further inspection. I was able to detect a fair amount of poa within the samples. The poa could be contributing to the yellow appearance but might not be the sole cause as yellow tuft can occur on most turfgrass species although it is most common in creeping bentgrass or annual bluegrass. Digging a little deeper, I was able to find clusters of tillers originating from a single crown. This symptom is characteristic of yellow tuft and is the result of a plant hormone released by the disease pathogen.
In this case, even though poa was present in the canopy, the yellow spots were probably mainly the result of yellow tuft. With all the rain most parts of the state have received the conditions that would favor yellow tuft development are favorable. Cultural controls for yellow tuft include ensuring adequate surface and subsurface drainage. As far as chemical controls, the mefanoxam (Subdue Maxx) and fosetyl-Al (Signature) are the only fungicides currently labeled for yellow tuft.
For a great article about other causes of yellow spots on putting greens check out this link to our friends at the Turf Disease Blog. Let’s hope the rain stops and the soil dries out a bit before the temperatures heat up again.
Graduate Research Assistant