Development of a commercially viable and environmentally sustainable approach to slug control

There is growing public and legislative pressure to reduce the use of pesticides in crop production. In arable fields, the grey field slug is unevenly distributed with patches of higher slug densities, interspersed within areas of lower slug numbers. Targeting molluscicide applications only at these patches (patch treatment), leaving other areas untreated, would substantially reduce molluscicide use for slug control. Building upon earlier AHDB funded work (student report 43), the aim of this study was to develop an approach by which these patches can be identified, and to develop a prototype patch treatment procedure that maintains effective slug control.

Extensive consultation with appropriate industry sectors (agronomists/farmers; soil assessment/mapping service providers; application technology/GPS manufacturers) informed all stages of the project. Liaison with industry players underpinned development of the patch treatment procedure through provision of advice on re-purposing soil assessment/mapping techniques and software for the system, state-of-the-art farm machinery, and commercial viability/constraints. Assessments were taken for field experiments by industry colleagues, and anonymised commercial datasets provided for analysis.

Of seven soil characteristics investigated, significant relationships were established between slug patch location and %clay, %silt, and soil organic matter. The cost of soil analysis can be reduced by using electroconductivity scans as a proxy for soil structure. Further testing in 2020/21 confirmed these relationships, demonstrating their potential to predict patch location. Field tests of a provisional patch treatment protocol showed that, in comparison to treating whole fields, patch treatment resulted in similar residual post treatment slug populations during the crop damage window, but with only 30% of the area receiving pellets.

Slug patch location was found to be stable providing a ‘standing target’ for control measures. Variation of soil structure factors across fields was stable for periods of up to eight years (despite regular cultivation), with organic matter also stable in unimproved fields. Thus, historical assessments can be used for patch treatment targeting avoiding the need for annual re-assessment and allowing re-use of soil maps made for other husbandry purposes.

A prototype patch treatment procedure was developed, which initial analysis shows results in considerable savings in the total crop area treated, addressing the sustainable crop production agenda. The principle operational costs are low, as the required soil assessment/mapping approaches are already used for other husbandry purposes, and the protocol uses available machinery/software. Savings, accrued from reduced molluscicide usage, have been incorporated into an initial cost-benefit analysis, which shows that the procedure has a positive effect on gross margin budgets for winter oilseed rape.