Hyperspectral radiometry for the detection and discrimination of damage caused by sucking pests of cotton

Use of remote sensing techniques for detection of crop stress due to pests and diseases is based on the assumption that stresses induced by them interfere with photosynthesis and physical structure of the plant, affect absorption of light energy and thus alter the reflectance spectrum of plants. Field experiments were conducted to detect and estimate damage caused by sucking pests in cotton (cv. Surabi) at regular intervals using GER1500 spectroradiometer, from which canopy reflectance was recorded and vegetation indices (VI) were worked out. There was a decrease in near infrared (770-860nm) while blue (450-520nm), green (520590nm) and red (620-680nm) reflectances increased compared to undamaged plants. The mean VI values in damaged plants were comparatively lower than undamaged plants in all days of observation. Among spectral bands, red band was highest to thrips and leafhopper damage while NIR band was found to be more sensitive to aphid damage. In the aphid damage sensitivity curves, the trough in green region was not very conspicuous while thrips and leafhopper damage curves had a clear low point in green region at 550 nm in all days of observation. Green red vegetation index (GRVI) was observed to be sensitive in differentiation of sucking pests damage.