Potassium (K) is an important nutrient for grape because it sustains charge neutrality during organic acid transport, is a major ion involved in osmoregulation and stomatal function and contributes to pH status in grapes and wines. We assessed the utility of a number of vegetation indexes for detection of K deficiency symptoms in a commercial vineyard of Vitis vinifera cv Pinot Noir. A hyperspectral field spectroradiometer for the 350-2500 nm spectral region was used to measure light reflectance at the leaf level. This data allowed us to screen a broad range of spectral indexes to detect absorption features affected by potassium deficiency symptoms. We found there were few indexes directly influenced by K deficiency symptoms. Absorption features in the visible region, centered at approximately 495 nm and within the chlorophyll b absorption feature at 625 nm were sensitive, and particularly after transformation to derivative spectra. Concentrations of K in leaves with visible symptoms ranging from 0% to more than 60% color change on leaf surfaces were not statistically significantly different (P  0.05). These results suggest that observed symptoms might have been the result of heat stress and resulting. Our results indicate that non-invasive monitoring using hyperspectral reflectance may be used for spatially constraining K deficiency for use in site- specific K applications with future investigations.