Utilising the patchy distribution of slugs to optimise targeting of control: improved sustainability through precision application (PhD)

Abstract

The grey field slug (Deroceras reticulatum) is an agricultural pest, causing economic damage to a range of crops in the UK. Legislation has led to a reduction of registered active ingredients and increased pressure to reduce pesticide usage. Discontinuous distributions of slugs in arable fields offers the potential to target control applications, reducing pesticide use, while maintaining efficiency. This report investigates the stability of patches and methods for locating them.

Significant aggregations of slugs were found at all field sites, with stable areas of higher slug densities occurring in the same area of the field at all five fields sites during the 2015–16 season. In the subsequent two seasons, slug numbers were lower. However, similar patterns of stability were observed in the fields with the largest populations. Stability of patches between seasons requires further work.

Alternative methods of locating areas of higher slug densities were investigated. Using crop damage from grazing was not found to be suitable. The highest correlation between slug numbers and damage was r = 0.52. No positive correlation was found in the field with the largest population. Using soil characteristics was also investigated, with organic matter, pH, bulk density and soil texture found to be significantly different at some field sites within and outside of slug patches, providing potential candidates for further investigation.

A method of identifying individual slugs was developed to improve understanding of patch formation. Radio frequency identification tags were used to track slugs in the field over two five-week periods. Slugs were found to remain close to their release point. The maximum distance moved from the point of release was 78.7 cm in April 2017 and 101.9 cm in November 2017.

The combination of results from this work suggests there is strong potential for targeting molluscicides to areas of higher slug densities.