Influence of synthetic phthalocyanine pigments on light reflectance of creeping bentgrass

Abstract

The use of synthetic pigment-containing products on golf playing surfaces by golf course superintendents has increased dramatically to provide green color and improve stress tolerance. Most turf colorants are synthesized from various phthalocyanine pigments, which share visible spectral properties with green plant tissue. Vegetation indices, such as normalized difference (NDVI), are commonly used by researchers to quantify plant health or turf quality. Research reports indicate that turf canopy reflectance is sometimes positively and sometimes negatively affected by synthetic pigments. The specific spectral wavelength used for vegetation indices varies by sensor type, which may explain these inconsistencies. A greater understanding of light absorption characteristics of synthetic pigments is needed. Therefore, the research objectives were to determine the spectral properties of synthetic phthalocyanine pigment-containing products alone and to quantify their influence on light reflected from treated creeping bentgrass canopies. Narrow bandwidth (1.5 nm) reflectance was collected from across visible and near-infrared spectra using a handheld field spectroradiometer (PSR-1100F, Spectral Evolution) to develop spectral signatures of pigmented products alone, healthy turf, and healthy turf treated with pigmented products. Synthetic pigment-containing products strongly absorbed near-infrared light but did not affect photosynthetically active spectra. Some products tested influenced reflectance of ultraviolet A radiation. Endogenous chlorophyll concentrations 7 d after treatment were not altered by products tested. Spectral characteristics of NDVI and similar reflectance measurements of creeping bentgrass quality using near-infrared light may be negatively affected when the turf is treated with phthalocyanine pigment-containing products.