Spectral response of cotton aphid- (Homoptera: Aphididae) and spider mite- (Acari: Tetranychidae) infested cotton: controlled studies.

Remote sensing is a precision tool that can detect plant health. Ground-based methods in small-scale experiments were used to explore the applicability of this technology for detection of arthropod-damaged cotton and to find useful indices or wavelengths for detecting arthropod-damaged cotton. Individual leaves of greenhouse-grown cotton plants and cotton plants in the field were infested with populations of cotton aphids, spider mites, and aphids + mites. Several sets of reflectance measurements were collected from the adaxial surface of the leaves at various intervals after infestation using a portable hyperspectral spectrometer with an integrating sphere or a contact probe. Vegetation indices were calculated from the reflectance values; these indices and the raw reflectance values, represented by narrow wavelength bands, were tested to see if arthropod damaged cotton could be distinguished from healthy cotton. Results indicated that it was possible to detect cotton aphid- and spider mite-damaged leaves by tracking the spectral changes in the leaf, although the damage type of each arthropod could not be distinguished spectrally. In addition, spider mite- and aphid-infested cotton leaves increased reflectance in the near infrared wavelength at approximately 850 nm in comparison to uninfested leaves.