Use of vegetation indices to detect plant diseases
Today's agriculture is not only confronted with the production of food and animal food, but also with aspects of environmental protection. In today's crop production, there is an increasing pressure to reduce the use of pesticides, to decrease the environmental impact and to lower potential production costs. It is therefore imperative that pesticides are only applied when and where needed. Disease control might be more efficient if disease patches within fields could be identified and fungicides applied only to infected areas. Recent developments in optical sensor technologies indicate the potential to enable direct detection of foliar diseases under field conditions ([We03]). In the context of this study different vegetation indices were evaluated for their potential to detect and identify different plant diseases. The influence of Erysiphe graminis (powdery mildew) and Septoria tritici (leaf blotch disease) on canopy refectance of winter wheat was analyzed in various field trials. Canopy reflectance was measured every 7 days starting from May until mid of July depending on the development of the plants. Reflectance measurements were carried out with a fieldspectroradiometer Field Spec$\textregistered $Hand Held (ASD, Inc. Boulder, CO, USA). Reflectance data was evaluated according to known vegetation indices in allegorized specified reflectance bands. Vegetation indices were evaluated for their suitability to detect differences in vitality between healthy and diseased plants and were used to compare the effectiveness of different sensor systems for the purpose of disease identification. From a multiplicity of existing vegetation indices the indices able to detect the relevant plant diseases were selected.
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