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.

Reduced creeping bentgrass fairway reflectance following synthetic colorant application

“…This PDSO+CPC residue perturbance of 810‐nm reflectance was also reported by McCall et al. (2020) in the 24 h following colorant application. Such absent NDVI response, often dependably correlated with turfgrass shoot growth in season (Dai & Schlossberg, 2008; Trenholm et al., 1999), further implicates artificial deflation of 810‐nm reflectance from PDSO+CPC treated plots over the 10‐d period following application to the fairway.…”

“…Similarly, McCall et al. (2020) report a chlorophyll index calculated using 531‐ to 570‐nm reflectance showed a significant increase in phthalocyanine colorant‐treated plots.…”

“…Similarly, cautionary reports pertaining to multispectral radiometric inference into turfgrass canopy characteristics have materialized. Notable preclusions consist of different turfgrass cultivars as well as identical cultivars either maintained at dissimilar heights of cut or evaluated in the 24‐h period immediately following spray application of a synthetic pigment (i.e., colorant or a colorant combination product) (Bremer et al., 2011; Lee et al., 2011; Leinauer et al., 2014; McCall et al., 2020; Obear et al., 2017).…”

“…Labels on three products evaluated by McCall et al. (2020)—Appear (Syngenta Prof. Products), Interface (Bayer Environmental Science), and Civitas Pre‐M1xed Turf Defense™ (Intelligro)—recommend 14‐d reapplication intervals through periods of concerning plant stress.…”

“…Synthetic colorants are commonly applied to golf course putting greens and fairways either as a spray pattern indicator or a combination product synergist (McCarty et al, 2013(McCarty et al, , 2014. McCall et al (2020) conferred an extensive review of synthetic colorant research on turfgrass systems before reporting similar phytoactivity across five phthalocyanine colorant containing products. Labels on three products evaluated by McCall et al (2020)-Appear (Syngenta Prof. Products), Interface (Bayer Environmental Science), and Civitas Pre-M1xed Turf Defense™ (Intelligro)-recommend 14d reapplication intervals through periods of concerning plant stress.…”