Disentangling the Effects of Intercropping on Vector-Borne Plant Virus Dynamics

Emerging plant diseases threaten crop yields, food security and the health of ecosystems. In fields with multiple plant species, disease management can become challenging, as different host plants can either reduce or increase virus transmission. Motivated by empirical evidence that intercropping tends to limit virus spread, we develop a mathematical model that integrates the epidemiological dynamics of multiple plants and a vector population. We derive the basic reproduction number and quantify how relative differences in intercrop characteristics determines outbreak persistence. We find conditions when intercropping reduces the average number of secondary infections from a plant compared to a monoculture. We also demonstrate cases where intercropping can increase the risk of a disease outbreaks. Crucially, even when disease persistence is unlikely, transient outbreaks may still occur. We investigate such short-term dynamics by deriving a threshold index that predicts when transient outbreaks are possible. We give conditions that ensure there are plant mixture compositions where persistent and transient outbreaks are unlikely in a monoculture and/or inter-cropped system. We discuss the practical implications of all our results, which provide a theoretical foundation for sustainable plant disease control.