Yellow Tuft

Yellow tuft can occur on all turfgrass species. It is sometimes referred to as downy mildew primarily on warm season turfgrasses. Where it is most noticeable and considered a problem or nuisance is on creeping bentgrass during spring and fall under cool (43 to 66 F) moist conditions.

Symptoms initially appear as a stunted growth and a thickening of the leaf blades. As the disease progresses small yellow patches the size of a fingertip appear; resulting in a yellow speckled looking turf. Symptoms are most often mistaken for nitrogen chlorosis, or a sudden infestation of annual bluegrass (Poa annua). Upon closer examination the infected plants have a proliferation of thickened shoots or tillers.

Photograph 1. Yellow tuft symptoms on a creeping bentgrass turf.

The pathogen, Sclerophthora macrospora is in the class oomycetes (water molds) and usually needs free water to spread when the fungus sporulates producing fruiting structures called sporangia. Usually when the plants turn yellow this is a sign that sporulation is active.

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Photograph 2. The creeping bentgrass plant on the right is showing symptoms of Yellow tuft. The plant on the left is uninfected with the fungus.

The fungus is also classified as an obligate parasite. In other words the fungus cannot live or complete its life cycle without a host (turfgrass plant). For this reason, this fungus will rarely kill the plants, which is good - but it also makes control difficult. Fungicide applications are almost always made curatively with complete control rarely achieved.

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