Optimizing vector and host control to improve management of an insect-borne plant pathogen

X-disease, a widespread plant disease critically impacting stone fruit across the United States, is caused by a phytoplasma that infects the phloem in trees and causes fruit to be small, bitter and unmarketable. Insect vectors, notably leafhoppers, acquire the X-disease phytoplasma during feeding on infected trees or weedy hosts that act as pathogen reservoirs. The phytoplasma replicates before it can be transmitted during subsequent feeding, so leafhoppers may acquire and transmit the causal phytoplasma between weeds and trees over an entire season. Methods to slow disease spread include tree removal, use of clean plant material during grafting, control of insect vectors, and control of weedy host reservoirs. In the past few years, greater attention has been brought to management of broadleaf weeds found in orchard cover, but it is unclear whether managing weeds or leafhoppers is most beneficial in slowing X-disease spread. To evaluate multiple strategies, a mathematical model was developed using a series of differential equations to predict acquisition and transmission of X-disease in leafhoppers, broadleaf weeds, and trees by manipulating three management strategies: control of weeds, control of immature leafhoppers, or control of adult leafhoppers. The model demonstrates it is more effective to only control immature or adult leafhoppers than broadleaf weeds. Controlling insects is key as combinations of weed and insect control reduce disease spread more than weed management alone. The model serves as a tool to simulate the use of pesticides at varied timepoints and reveal the impact of applications on disease spread.