Abstract:

【Objective】 The effects of the damage degree, spatial pattern, and rate of damaged leaves by rice leaf roller (RLR) on spectral characteristics of leaves were studied in this paper in order to construct models for diagnosing the damage of rice, and to attain the parameters and methodology for automatic monitoring of the rice leaf roller. 【Method】 The spectral reflectances of different damage degrees, spatial patterns and damage rates of rice leaves were measured by ASD Hand-held Spectroradiometers, and the diagnosing models based on the spectral parameters were established using the linear regression method. 【Result】 The results indicated that the spectral reflectance of rice leaf decreased in the green (530-570 nm) and near-infrared (700-1 050 nm) wave-length regions with the increase of the damage degree whereas it increased in the red wave-length region (610-700 nm). The regions of 530-564 nm, 614-695 nm and 706-1 050 nm were the sensitive wave-length bands which could reflect the impaired level of rice leaf by the RLR. Five models were established for diagnosing the damage degree of rice leaf, and their diagnosing accuracies were 80%-90%. The maximum diagnostic accuracy belonged to the model based on the reflectivity at 741 nm. The spectral reflectance of rice leaves was less impacted by the spatial pattern of the damaged leaves when the rate of the damaged leaves was constant. However, the spectral reflectivity increased significantly at 450-500 nm and 610-700 nm, but decreased at 530-570 nm and 700- 1 050 nm as the rate of damaged leaves increased. The spectral indexes including vegetation index (Rnir-Rred), the areas of the yellow-edge (SDy), and the difference of the areas of the red-edge and blue-edge (SDr-SDb) could significantly distinguish the six grades of leaf roll rates (0%, 10%, 30%, 50%, 70%, and 90%). The area of yellow edge (SDy) index could diagnose the leaf roll rate and the accuracy of diagnoses was up to 86%. 【Conclusion】 The damage of rice leaves by RLR could be monitored by the spectral reflectance. Spectral indexes could reflect the harm degree of rice leaves and the rate of infested leaves.

Key words: rice')">rice, rice leaf roller, damaged degree, infestation leaf rate, spatial pattern of damage leaves, spectral reflectance, diagnostic model