Measurements of Citrus Tree Health with a Scanning Densitometer from Aerial Color Infrared Photographs. C. H. Blazquez, University of Florida, Institute of Food and Agricultural Sciences, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred 33850. Plant Dis. 75:370-372. Accepted for publication 2 October 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0370.

Aerial color infrared (CIR) photographs of citrus trees were analyzed with a scanning densitometer (SCND) to obtain spectral curves for comparison with arbitrarily assigned visual grades (VG). Spectral curves derived from healthy and declining tree rows had one peak at 500–520 nm and another between 600 and 620 nm. Comparisons between VGs and integrals (peaks I 1 and I 2) showed little difference between them, nor between VGs and percentage of transmittance values (T 1 and T 2). Spectral ratios of the integrals (SRG) and spectral transmittance (SRT) separated the VGs into three different groups, suggesting that a reduction from five to three VGs would make densitometric measurements more realistic.