| Brown planthopper is a major pest on rice,and its damage can lead to serious loss of rice yield.The early monitoring of brown planthopper is beneficial to the control of pests and can better ensure the normal growth of rice.Therefore,this paper studied the relationship between the change of rice canopy temperature and the number of BPH and rice yield,and combined with the canopy spectral technology,in order to establish a simple new monitoring method for brown planthopper.The main results were list as followings.The canopy temperature of rice damaged by BPH was measured by thermal imaging technology.It was found that there was a good correlation between the highest canopy temperature and the number of BPH in rice plots.The canopy temperature measured at 50-90 cm away from rice canopy indicated that the stability of brown planthopper population on rice was better.The change of measurement angle of thermal imager will not affect therelationship between canopy temperature and the number of BPH.Two consecutive years of measurement found that the canopy temperature measured during the rice growing season from 8:00-10:00 am was significantly negatively correlated with the amount of insects,while the temperature at noon and afternoon was not significantly correlated with the amount of insects.The layer temperature to monitor the number of BPH needs to be carried out in the morning.There is a close relationship between the canopy spectral reflectance and the brown locust population at the 400-725 nm,765-1000 nm and 625-675 nm bands in the booting,heading and flowering stages of rice,respectively.Within 16-18 days after insecticide inoculation,the relationship between the spectral index of rice canopy and the number of BPH was not significant,but after that most spectral indexes were significantly correlated with the amount of brown planthopper,and the spectral indexes of CARchap,DSSI1,NDVI,PSSRa,PSSRc,RVI730-670 were always highly correlated with the number of BPH,which could better reflect the damage of rice caused by brown planthopper.The diagnostic accuracy of the model was 67.6%by using 29 spectral indices and the number of BPH as stepwise regression models.The diagnostic accuracy of the model was 57.1%by using the canopy temperature and the number of BPH alone.However,when the canopy temperature index was added to the spectral index regression model,the highest diagnostic accuracy of the model could be increased to 71.4%.Therefore,rice canopy temperature index has the potential to monitor the population of rice brown planthopper.The access to rice planthopper on rice seriously affected the yield of rice.The larger the number of insects,the lower the rice yield in the plot.There was a significant positive correlation between the number of BPH and the yield loss rate at 18-80d and 25-85d after 2017 and 2018 respectively.The correlation coefficient reached the maximum at 55d and 59d respectively.The highest temperature of rice canopy had the best correlation with rice grain quality,and the highest correlation was found at booting and heading stage.Among the 29 spectral indices selected,the spectral index and rice yield loss rate did not reach significant levels before and after 18 days and 25 years,respectively,before reaching significant levels,among which CARchap,Ch1 index,PSRRa,PSSRc,Red The six spectral indices of edge and RVI730-670 have always maintained a very significant correlation with the amount of brown locust,which can better reflect the loss rate of rice yield.The stepwise regression model of 29 spectral indices and rice panicle and grain quality was established.The diagnostic accuracy of the model was 71.4%for two consecutive years.The diagnostic accuracy of the model was 57.1%only by using canopy temperature and rice panicle and grain quality.The diagnostic accuracy of the model could be increased to 75%by adding canopy temperature index to the spectral index model.Therefore,rice canopy temperature index has the ability to reflect the extent of rice damage by brown planthopper.In conclusion,rice canopy temperature has the ability to monitor the amount of brown planthoppers and rice yield.Combining the highest temperature of rice canopy with various spectral indicators can improve the accuracy of model monitoring brown locust and rice yield. |
