Soybean Aphid Mapping and Monitoring
Soybean aphids damage can be assessed by applying Landsat imagery. Typically throughout the soybean reproductive stage, soybean fields are associated with a distinctly greater NIR reflectance than cornfields (about 15 - 20 percent more), in large part due to tassels (top image). When aphids harm soybean plants, NIR reflectance can become similar to or less than cornfields (middle image). The top image is in northwestern Ohio on 8/19/03; the middle image represents the same spatial extent on 8/27/03. In the middle image, eight days later, soybean and corn fields have similar reflectance due to the effect of soybean aphids. Individual field maps of soybean aphid damage can be produced by subtracting NIR images (earlier image - later image) as shown in the bottom image. Subtracting NIR based on digital numbers will produce a map with the same appearance as applying reflectance, but reflectance can quantify/estimate the damage.
Map of soybean aphid damage for field based on decreased NIR (arrows above points to field). Darker shades correspond to a greater decrease in NIR reflectance and more damage by soybean aphids; squares show 30 x 30 meter Landsat pixel extent.
