A tool predicting how to protect European citrus from HLB shows how mathematical modeling can help prepare for future plant disease invasions.
Europe is currently unaffected by HLB. However, there are increased concerns of an infestation since psyllids that spread HLB have been found in key citrus-producing countries, including Portugal and Spain.
In response to the HLB threat, a new study involving researchers at the University of Cambridge uses mathematical modeling to test a range of strategies for detecting and controlling the disease in Europe. The study has found that early detection and effective pest control will be key to reducing the impact of the disease. The research was published in Plants, People, Planet on Feb. 24.
Nik Cunniffe, head of the Theoretical and Computational Epidemiology group at the University of Cambridge and an author of the paper, said modeling provides a way to make predictions about the spread, detection and control of a plant disease.
“For emerging pathogens — those which cause disease in new places or on new host species — modeling has very often been done retrospectively,” Cunniffe said. “Too often the story is very late detection of a pathogen and bungled or sometimes non-existent attempts to control. Here, we focus on modeling in advance of an invasion and show that models can make a useful contribution in terms of translating information on spread elsewhere to recommendations for disease management even for a pathogen that has not yet entered.”
The research shows that early detection of HLB in Europe is key. Cunniffe’s team predicts that once the disease reaches Europe, large areas will become infected within 10 to 20 years without disease management. Even with significant visual surveillance, the epidemic would already be widespread on first detection, making eradication very unlikely.
Removing infected fruit trees and intensive insecticide use could sustain some citriculture for a decade or more, albeit with reduced production. However, effective control may require chemical application rates or active substances no longer authorized in Europe.
The study shows that strategies targeting non-symptomatic infection will be most successful.
One promising solution is to test psyllids to see if they are carrying bacteria which cause the disease. This could be an effective early-warning mechanism before plants show symptoms of infection and could reduce lags before disease management starts.
If detection of insects carrying HLB were followed by intensive insecticide sprays as well as tree removal, this could greatly improve outcomes.
Modeling work for HLB is now being extended at the University of Cambridge by Laura Erbetta, a Ph.D. student in the Theoretical and Computational Epidemiology group. The idea is to generalize the model of HLB to other countries and to other species which transmit the disease — in particular, the Asian citrus psyllid which has recently invaded Cyprus. The project will also test more elaborate strategies for detection and control.
Source: University of Cambridge Department of Plant Sciences
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