Detection of sugarcane African stalk borer Eldana Saccharina Walker (Lepidoptera:Pyralidae) using hyperspectral remote sensing (spectroradiometry)

The South African sugar industry is one of the world's leading sugarcane producers. The stalk borer Eldana saccharina has for many years been the most destructive pest in the South African sugar industry and is the most important factor limiting sugarcane productivity. The pest has been monitored using a traditional visual approach whereby a representative sample of stalks is taken from a field and split longitudinally to assess damage and count the number of E. saccharina. This approach is time-consuming, labour intensive and sometimes biased as, in some instances, only easily accessible areas are surveyed. To investigate a more economical but equally sensitive survey methodology, this paper aims at determining the potential use of hyperspectral remote sensing (spectroradiometry) for identifying sugarcane infested by E. saccharina. A hand-held ASD (Field Spec® 3) spectroradiometer was used to take leaf spectral measurements of sugarcane plants from a potted-plant trial taking place under shade house conditions. In this trial, nitrogen and silicon fertiliser applications as well as varieties used were known. In addition, watering regimes and artificial infestation of E. saccharina were carefully controlled. Results illustrated that severe E. saccharina infestation increased reflectance throughout the whole spectrum range (400-2500 nm). E. saccharina stalk damage was also linearly related to modified normalized difference vegetation index (mNDVI) using R2025 and R2200 (R2=0.69). It was concluded that hyperspectral data has a potential for use in monitoring E. saccharina in sugarcane rapidly and non-destructively under controlled conditions. A follow-up study is recommended in field conditions and using airborne and/or spaceborne hyperspectral sensors.