The effect of 60% shading and nitrogen (N) source on growth, tissue NH<sub>4</sub><sup>+</sup> and NO<sub>3</sub><sup>-</sup> concentrations, and inflorescence necrosis (IN) was investigated in one- and two-year-old potted Pinot noir grapevines. New growth of the vines was significantly reduced by shading and NH<sub>4</sub><sup>+</sup> feeding resulted in less new growth compared to NO<sub>3</sub><sup>-</sup> feeding. The shaded two-year-old vines developed 26.6% IN compared to only 0.6% on unshaded vines. No IN was induced by either NH<sub>4</sub><sup>+</sup> or NO<sub>3</sub><sup>-</sup> feeding treatments. Shading increased tissue NH<sub>4</sub><sup>+</sup> concentration in most tissues of one-year-old vines with few exceptions and in laminas, petioles, and rachis of two-year-old vines. Two-year-old vines fed NH<sub>4</sub><sup>+</sup> and/or NO<sub>3</sub><sup>-</sup> had a higher rachis, petiole, stem, and young root NH<sub>4</sub><sup>+</sup> concentration at post-anthesis, compared to the no N control. The NH<sub>4</sub><sup>+</sup>-fed vines had a higher NH<sub>4</sub><sup>+</sup> concentration than that of NO<sub>3</sub><sup>##</sup>-fed vines only in stems at post-anthesis and young roots pre-anthesis, anthesis, and post-anthesis. Tissue NO<sub>3</sub><sup>-</sup> concentration of laminas, petioles, stems, and young roots was proportional to the amount of NO<sub>3</sub><sup>-</sup>-fed to the vines in the root medium. Elevated tissue NH<sub>4</sub><sup>+</sup> concentration in the rachis of shaded vines and increased incidence of IN suggest that IN is associated with elevated tissue NH<sub>4</sub><sup>+</sup> levels. NH<sub>4</sub><sup>+</sup> and/or NO<sub>3</sub><sup>-</sup> in culture media is not a source of elevated NH<sub>4</sub><sup>+</sup> level for IN development.