Detection of powdery mildew in two winter wheat cultivars using canopy hyperspectral reflectance.
To determine the most sensitive spectral parameters for powdery mildew detection, hyperspectral canopy reflectance spectra of two winter wheat cultivars with different susceptibilities to powdery mildew were measured at Feekes growth stage (GS) 10, 10.5, 10.5.3, 10.5.4 and 11.1 in 2007-2008 and 2008-2009 seasons. As disease indexes increased, reflectance decreased significantly in near infrared (NIR) regions and it was significantly correlated with disease index at GS 10.5.3, 10.5.4 and 11.1 for both cultivars in both seasons. For the two cultivars, red edge slope (drred), the area of the red edge peak (Σdr680-760 nm), difference vegetation index (DVI) and soil adjusted vegetation index (SAVI) were significantly negatively correlated with disease index at GS 10.5.3, 10.5.4 and 11.1 in both seasons. Compared with other parameters, Σdr680-760 nm was the most sensitive parameter for powdery mildew detection. The regression models based on Σdr680-760 nm were constructed at GS 10.5.3, 10.5.4 and 11.1 in both seasons. These results indicated that canopy hyperspectral reflectance can be used in wheat powdery mildew detection in the absence of other stresses resulting in unhealthy symptoms. Therefore, disease management strategies can be applied when it is necessary based on canopy hyperspectral reflectance data.