Submitted to: International Journal of Remote Sensing
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/27/2003
Publication Date: 10/10/2004
Citation: Fletcher, R.S., Escobar, D.E., Skaria, M. 2004. Response of ratio vegetation indices to foot-rot infected citrus trees. International Journal of Remote Sensing. 25(19):3967-3972. Interpretive Summary: Foot rot infection causes citrus tree decline that results in yield reduction in south Texas citrus orchards. Visible, near-infrared, and mid-infrared light reflectance from tree canopies of healthy and mild foot rot-infected citrus trees were obtained to evaluate the usefulness of this information for differentiating between the trees. The ratio of the visible red to near-infrared light reflectance was the most effective for distinguishing healthy from infected trees. These findings should benefit agricultural consultants, extension agents, citrus growers, and commercial industries dealing with remote sensing technology. Also, the detection of these mildly infected trees will permit citrus growers to apply treatments that not only prolong the lives of the infected trees, but their yields as well.
Technical Abstract: This study explored the potential of thematic mapper (TM) spectral bands and band ratios for detecting citrus (Citrus spp.) trees having mild symptoms (10 to 30% foliage loss) of foot rot infection (Phytophthora parasitica Dast). Field reflectance measurements of healthy and infected trees were obtained from two south Texas citrus groves with a field spectroradiometer that simulated the blue (TM1), green (TM2), red (TM3), near-infrared (TM4), and mid-infrared (TM5 and TM7) TM bands. A ratio of the red to the near-infrared band (TM3/TM4) was the most effective for distinguishing between healthy and mildly infected trees. Thus, it would appear that airborne multispectral imaging systems equipped with filters identical to TM3 and TM4 should have the potential for detecting and/or discriminating healthy citrus trees from citrus trees exhibiting mild symptoms of foot rot infection. These results should be beneficial to agricultural consultants, extension agents, citrus growers, and commercial industries.