Modelling the Spatial Variation in Alopecurus myosuroides for Precision Weed Management

Alopecurus myosuroides Huds. (black-grass) grows in patches within fields. This presents an opportunity for site-specific management by patch spraying. Despite the economic and environmental benefits of this type of management, it is not being readily taken up by farmers, largely due to the risk of missing weeds that fall outside of established patches. I focus on the environmental determinants of patch location in A. myosuroides and the scale-dependence of relationships between A. myosuroides and environmental properties. Understanding these relationships allowed me to determine which abiotic factors can be used to identify A. myosuroides vulnerable zones within fields and if these relationships occur at scales appropriate for management. This presents a more conservative approach than patch spraying according to observations of previous years’ infestations, as a greater area of the field is sprayed, yet the overall use of pesticide is still reduced.

By combining field work, pot experiments, and modelling, I discovered that soil organic matter, water, and pH, amongst other environmental properties, show strong scale-dependent relationships with the within-field distribution of A. myosuroides. These relationships between A. myosuroides and soil properties were often strongest at coarse scales making them particularly useful for the implementation of management practices, which are often limited to coarse-scale implementation by the available machinery. The effects of these soil properties on A. myosuroides are both direct (affecting the plant’s life-cycle) and indirect (altering herbicide efficacy). The incremental changes I observed to different aspects of the life-cycle due to soil properties may seem too small to be of consequence when studied independently, yet when combined in a modelling approach their additive nature revealed them as important determinants of the within-field distribution of this species and the coarse-scale relationships observed in the field are an emergent property of the model.