Plant canopy temperature and multi-spectral reflectance are measured with a wireless multi-band sensor, and the temperature data are qualified and the spectral reflectance measurements are classified. The multi-band sensor includes sensors for measuring plant canopy temperature radiation and spectral reflectance over five bands, a microprocessor to receive and store measured data, and a wireless transmitter for transmitting data from the microprocessor to a remote receiver, all enclosed within a single housing. The data are used to detect variations in spectral signature due to plant stress (e.g., disease, water stress) and due to soil background and to qualify temperature data accordingly. The data provide information for decision support algorithms related to the initiation of automatic irrigation scheduling as a function of crop canopy cover, qualification of temperature data used in automatic irrigation scheduling algorithms, and detection of diseased crops for the purpose of withholding irrigations when yield potential is compromised.