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Title: FIELD SPECTRA AND AIRBORNE DIGITAL IMAGERY FOR DETECTING PHYTOPHTHORA FOOT ROT INFECTIONS IN CITRUS TREES

Author
item Fletcher, Reginald
item MANI, SKARIA - TX A&M CITRUS CTR-WESLACO
item Escobar, David
item Everitt, James

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: This study evaluated the use of the latest remote sensing technology, that of airborne digital imagery, for the detection of citrus trees depicting mild symptoms of foot infection. Ground reflectance measurements were acquired to determine the visible and near-infrared (NIR) spectral reflectance differences between the healthy and infected trees and these measurements were also used to help interpret the digital imagery. The CI digital imagery distinguished the infected from the non-infected trees. The non-infected trees had a bright red magenta color rendition, while the infected trees had a dull grayish red tonal response. These results indicated that digital imagery has potential use for detecting foot rot-infected trees in citrus groves. The advantage of airborne digital imagery is its real-time survey for quick field assessment. Thus, the findings of this research should be useful to citrus growers, extension officers, pathologists, and surveyors who are interested in using airborne digital imagery for the detection of foot rot infections in citrus orchards.

Technical Abstract: Phytophthora foot rot, caused by Phytophthora parasitica (Dast), can result in economic losses for the citrus industry in the Lower Rio Grande Valley of Texas. Therefore, locating foot rot-infected trees in citrus groves is important to citrus growers. This study evaluated the use of the latest remote sensing technology, that of airborne digital imagery, for the edetection of citrus trees depicting mild symptoms of foot rot infection. Airborne color-infrared (CIR) digital imagery was acquired of two citrus orchards having problems with foot rot infection. In addition to the aerial digital imagery, ground spectroradiometric measurements were conducted to determine the visible and near-infrared (NIR) spectral reflectance differences between the healthy and infected trees. These field reflectance measurements were also used to help interpret the color tonal renditions between the trees. The CIR digital imagery distinguished infected from non-infected trees. The non-infected trees had a bright red magenta color rendition, while the infected trees had a dull grayish red tonal response. The NIR spectroradiometric and digital data for infected trees were significantly lower than the healthy trees (P=0.05), whereas the visible reflectance and digital data revealed no significant differences between the trees. The infected trees' dull tonal response in the CIR image was attributed to their lower NIR light intensity. These results indicated that digital imagery has potential use for detecting foot rot-infected trees in citrus groves due to the NIR spectral differences that exist between infected and healthy citrus trees. The advantage of airborne digital imagery is its real-time survey for quick field assessment.