Technical Note: Response of ratio vegetation indices to foot rot-infected citrus trees

Abstract

Ratio vegetation indices were evaluated for differentiating foot rot-infected (Phytophthora parasitica Dast) from noninfected citrus trees (Citrus spp.). At two sites, field spectral measurements of infected and noninfected trees were obtained with a hand-held spectroradiometer. The following bands were assessed for developing the ratios: blue (B, 450–520 nm), green (G, 520–600 nm), red (R, 630–690 nm), near-infrared (NIR, 760–900 nm) and mid-infrared (MIR1, 1550–1750 nm; MIR2, 2080–2350 nm). For both sites, means of infected and noninfected trees were significantly different (t-test; p<0.05) for NIR/B, NIR/R and NIR/MIR1 ratios. Percentage difference values indicated the NIR/R ratio was most responsive to the disease. A relative index value was established for separating infected from noninfected trees. Findings demonstrated that ratio vegetation indices have high potential for distinguishing foot rot-infected from noninfected citrus trees.

Acknowledgments

We thank M. Alaniz, I. Cavazos, F. Gomez and J. Forward for their assistance in collecting field reflectance measurements, and D. Thompson and J. Gamble for allowing us to collect data from their orchards.

Notes

¹Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the United States Department of Agriculture.