Human beings are distinguished among mammals in having "trichromate vision," which is to say that we have three different types of opsins, the pigment that is sensitive to different wavelengths of light. Other mammals that have color vision have just two opsins, but most birds have four, giving them a very wide range of the electromagnetic field to which they respond. How does this correspond to color vision?
The colors we see are actually reflected wavelengths of light. Photo of Las Vegas Springs Preserve courtesy: Helen M. Stone
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Light is one portion of the electromagnetic field. As light hits an object, some of the light energy will be absorbed, and the rest will be reflected. We "see" an object by virtue of the light that the object reflects back to our eye. An object that is "green" to us is absorbing all the red and blue wavelengths and reflecting back the green wavelength (~500nm).
We can say that color is perceived when a unit of light energy (photon) is reflected by an object, acts upon an organism that is sensitive to that wavelength and the organism responds specifically to it.
Well, if you have those bright yellow rings on annual or rough bluegrass and it’s between 65 and 90 degrees F, there's a good chance you have some brown ring patch (aka Waitea patch). Recent research in Arizona and New Jersey has shown that this disease has also started recently to become a problem on creeping bentgrass as well.
A classic photo of the showing the yellow rings typically associated with the initial stages of brown ring patch on Poa greens. Photo courtesy: Pat Gradoville, Palos Verdes Golf Club.
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Brown ring patch is caused by Waitea circinata var. circinata, a species that looks and acts a lot like Rhizoctonia solani, the cause of regular ‘brown patch’ on cool and warm season turf and ‘large patch’ on warm season turf. In fact, high temperature brown patch aka ‘leaf and sheath spot’, although known as Rhizoctonia zeae is actually Waitea circinata var. zeae, and is closely related to the brown ring patch pathogen.
On annual and rough bluegrass, symptoms can look a lot like yellow patch or even the early stages of southern blight or fairy ring. A definitive diagnosis should be made - but bright yellow rings with a slightly green ring inside of that are good symptoms of brown ring patch on annual and rough bluegrass greens. As the disease progresses, the rings can turn brown to reddish brown and sunken, giving greens a soft mushy feel.
