Detection of pasture pests using proximal PA sensors: a preliminary study investigating the relationship between EM38, NDVI, elevation and redheaded cockchafer in the Gippsland region

Abstract

The redheaded cockchafer ('Adoryphorus couloni') (Burmeister) (RHC) is an important, native soil-borne pest of improved pastures in South Eastern Australia. The aim of this preliminary investigation was to determine whether commonly used Precision Agriculture (PA) sensors could identify landscape attributes that correlate with RHC population density. Soil apparent electrical conductivity (soil ECa) measurements were derived from EM38, relative photosynthentically-active biomass via the normalised difference vegetation index (NDVI) derived from an Active Optical Sensor (AOS) and elevation measurements derived from dGPS (differential global positioning system) mapping. Eight paddocks across seven properties in the Gippsland region of Victoria were surveyed using a Geonics EM38, CropCircle™ AOS and a dGPS. Eighteen to twenty sample sites in each paddock were selected based on different zones of soil ECa, and the RHC (and other cockchafer species) populations were assessed at each of these sites. No RHC were found in East Gippsland confirming that the damage to pasture observed by farmers at this time was caused by a different cockchafer species. Few RHC were found across all sites, probably due to high rainfall, however correlations tended to suggest that RHC were more likely to establish or survive in areas of high elevation and low soil ECa. On one property RHC were associated with low NDVI values and at one other high NDVI suggesting more complex relationships may exist between AOS data and RHC densities. Threshold-level relationships were apparent between RHC density and elevation and ECa to suggest that a useful indicator of pest risk could be developed, at least for some areas of Gippsland, however the relationships are complex and need to be investigated further.