MAPPING PHYMATOTRICHUM ROOT ROT OF COTTON USING AIRBORNE THREE-BAND DIGITAL IMAGERY

Abstract

Phymatotrichum root rot, caused by the fungus Phymatotrichum omnivorum, is a serious and destructive diseasethat significantly reduces cotton yield and lowers lint quality. Cultural practices are commonly recommended for the controlof cotton root rot, and fungicides and fumigants that may suppress the disease have also been used. Because of the high costsof these chemicals, their use may be economically feasible only when the infested portions of the field are treated. Theobjective of this study was to evaluate airborne multispectral imagery for detecting and mapping root rot areas in cotton fieldsfor site-specific management of the disease. One center-pivot irrigated field and one rainfed field near Corpus Christi, Texas,were selected for this study. Airborne three-band digital imagery was taken from the two fields shortly before harvest in 2001when the infested areas with wilted and dead plants were almost fully pronounced for the season. The imagery wasgeoreferenced and then classified into healthy and root rot areas using unsupervised classification. Accuracy assessment onthe classification maps for the two fields indicated that airborne imagery effectively and accurately identified root rot areaswithin the fields. Ground samples taken from the fields showed that cotton yield and some lint quality indices were significantlylower in root rot areas than in healthy areas. Buffer zones around the root rot areas were generated to account for the spreadof cotton root rot on the classification maps. The mapping procedures and maps presented in this study will be useful forsite-specific management of the disease.