Evaluation Of Bio-control Efficacy Of Alligatorweed And Ragweed By The Canopy Spectrum Reflectance

The canopy spectrum reflectance of two invaded weeds,Alternanthera philoxeroides and Ambrosia artemisiifolia,were measured after being fed by their biological control agents (Agasicles hygrophila and Ophraella communa). The Multispectral Radiometers (MSR) was used to collect the canopy spectrum reflectance of weeds at different damage level, and the leaf feeding rate were surveyed meanwhile. The relation between leaf feeding rate and canopy spectrum reflectance was definituded, and the main conclusions were summarized as follows:1. The effect factors on the scanning of MSRSome effect factors, as weather condition, solar elevation angle, instrument height and leaf moisture, could affect the scanning data collected by MSR. The spectrual scanning experiment should be carried at 10:00 am to 14:00 pm in sunny day and 1.3m height of instrument probe from weed canopy was selected, the experimental error can be reduced under the appropriate solar elevation angle and leaf moisture.2. The effect of the density of A. hygrophila and its control efficiency on the reflectance of A. philoxeroidesThe canopy reflectance was decreased with the density of A. hygrophila increasing at the green wave band (center wavelength 560nm) and near-infrared band (center wavelength 810nm) , whereas increased at wave band (center wavelength 660nm). The change range of reflectance at green wave band and red wave band were not significant comparing to that in near-infrared wave band. The high negative correlation ( r = -0.92, p<0.01) was found between the canopy spectral reflectance and the control effect of A. hygrophila. At near-infrared band (center wavelength 810nm) , the near-infrared band (the wavelength range from 760nm to 810nm) was considered the sensitive wave band, and could be applied to monitor control efficiency of A. hygrophila against the alligator weed A. philoxeroides.3. The relation between the vegetation index of A. philoxeroides and the density of A. hygrophilaThe leaf area and chlorophyll content of alligator weed, A. philoxeroides were decreased, the canopy spectral reflectance was changed after being feed by the flea beetle A. hygrophila, and resulted in the vegetation index of alligator weed changed. The significant differences of vegetation index were showed with different densities treatments of the flea beetle A. hygrophila.4. The ralation between the reflectance of A. artemisiifolia and the control efficiency of O. communaThe canopy reflectance was decreased with the feeding degree increasing at the green wave band (center wavelength 560nm) and near-infrared band (center wavelength 810nm), whereas increased at the red wave band (center wavelength 660nm), the significant differences between all treatments and the control group were observed. The high negative correlation(r=-0.82、-0.87 and -0.76, P<0.01) between the canopy spectral reflectance and feeding degree of O. communa were found in visible spectrum region (wavelength 560nm) and near-infrared region (wavelength 710nm and 760nm). The visible spectrum region (wavelength 560nm) and near-infrared band (wavelength 710nm and 760nm) were considered the sensitive wave bands, and could be applied to monitor control efficiency of O. communa against A. artemisiifolia.5. The ralation between the chlorophyll concent of A. artemisiifolia after fed by O. communaThe chlorophyll concent of A. artemisiifolia was significantly decreaded after fed by O. communa. The fitting equation on the chlorophyll concent with the reflectance of ragweed at 560nm wavelength was y=0.0624x1.6395 (R~2=0.7554).