The Relationship Of Rice Reflectance And Chlorophyll SPAD Values With Damage Degree Of The Rice Leaf Folder

The harm of rice leaf folder has always been an important factor that affects yield of rice.For a long time,the predication of rice leaf folder is a major work in pest forecasting departments in China.Before 1960s,rice leaf folder caused a minor damage,and in 1960-80s,it significantly developed and became a major pest in rice and caused heavy losses of the rice.Even though the harm became minor at the end of 1980s,the population outbreaks often occurred and rice leaf folder became an important pest again in rice.At present,monitoring methods for rice leaf folder still rely on manual counting and visual examination.Therefore,it is necessary to study an efficient,accurate and labor-saving method to monitor the damage of rice.In this paper,we investigated the possibility of using hyperspectral and SPAD method to monitor the damage degree of rice caused by rice leaf folder,and obtained the following results:The results of field monitoring showed that there was a significant correlation between the canopy spectral reflectance and the leaf-roll rates that at jointing stage and flowering stage.In addition,bands with significant levels and extremely significant levels were located at 700-1000 nm in the near infrared region.The leaf-roll rates at the booting stage and the jointing stage were significantly correlated with the reflectance of the green zone(577-492nm)and the red zone(622-770nm).Moreover,the leaf-roll rates at the jointing stage and at the flowering stage had significant correlations with the first order differential of reflectance in the red zone(622-770nm)and green zone(492-577nm),respectively.Based on all models built to monitor the leaf-roll rates at flowering stage and had been infected by the rice leaf folder for 48 days,the results showed that the equation Y=1.302-2.851 NDVI(573,440)(R2 = 0.65**)had the best modeling results,and the diagnostic accuracy was the highest,which was 87.5%.The results also showed that another equation Y = 1.1115-0.3404GI(R2 = 0.77**)had the accuracy of 75%,in which the rice was tested after 31-day infection by rice leaf folder and at the booting stage.Furthermore,the relationship between leaf chlorophyll SPAD and leaf-roll rates was significant,and there was a strong correlation between them.There also was a significant correlation between SPAD value and rice canopy spectral reflectance.The correlation degree increased with the increase of leaf-roll rates,and the correlation was related to 4 days,8 days,11 days and 18 days after infection.There is a band that reached a significant level,it can be concluded that this study is expect to be used in future forecast about rice leaf folder.