Major citrus blackfly (Aleurocanthus woglumi) outbreaks occur periodically in the Lower Rio Grande Valley (LRGV) of Texas, causing a reduction in citrus (Citrus sp.) tree yields. This research reports on the integration of airborne color-infrared (ACIR) imagery and geographic information system (GIS) technology for mapping citrus blackfly outbreaks appearing in this area in separate years. For this study, the 1993 and 2002 citrus blackfly infestations were mapped and compared. Outbreaks did not appear at the same sites for 1993 and 2002. In 1993, infestations occurred in the southern part of Hidalgo and Cameron counties compared with outbreaks primarily appearing in the western portion of Hidalgo County in 2002. For both years, Hidalgo County was affected more than the other citrus producing counties in the LRGV. This study demonstrated airborne remote sensing imagery integrated with GIS technology could be used to develop maps for comparing citrus blackfly infestations appearing in separate years.
Reginald S. Fletcher, James H. Everitt, Michael R. Davis and David E. Escobar
Reginald S. Fletcher, Mani Skaria, David E. Escobar and James H. Everitt
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. Symptoms of the infection include leaf yellowing, canopy defoliation, twig dieback, and short growth flushes. This study evaluated the use of the latest remote sensing technology, that of airborne digital imagery, for the detection of citrus trees exhibiting mild symptoms of foot rot infection. Airborne color-infrared (CIR) digital imagery of two citrus orchards having problems with foot rot infection was acquired. In addition to the aerial digital imagery, ground spectroradiometric measurements were conducted to determine the visible and near-infrared (NIR) spectral reflectance differences between healthy and infected trees. These measurements were also used to help interpret the color tonal renditions between the trees. The CIR digital imagery distinguished infected from noninfected trees. The noninfected trees had a bright red-magenta color rendition, while the infected trees had a dull grayish red tonal response. The NIR spectroradiometric and digital readings were significantly lower for infected trees than for healthy ones (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 for detecting foot rot-infected trees in citrus groves based upon NIR spectral differences. The advantage of airborne digital imagery is its real-time survey for quick field assessment.