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Jon West, Rothamsted Research, Harpenden, UK   

Surveillance and monitoring are important parts of integrated pest (and disease) management to enable interventions when long-term strategies like crop rotation and use of resistant varieties have not been effective enough.  A bewildering range of air sampling devices are available to detect airborne plant pathogens and more broadly to study the aerobiome.  These sample different volumes of air with different sampling efficiencies, which can bias results for example by omitting collection of smaller spores.  Dilution of spores as they disperse in air means we can infer whether the source is close-by or distant by comparing the concentration of spores sampled at two heights.  If the concentrations are similar, the spores come from a distant source but if there is a much greater concentration of spores close to the ground, it means the source is relatively close.  We have shown that the species diversity at 10m height is about double that of 1m due to air at 10m being more mixed by turbulence, representing a larger ‘footprint’.  The number of samplers needed per farm or region depends on the pathogen species and density of cropping.  Increasingly networks of samplers are being used to monitor disease risk.  There is a trend for these to be automated using optical methods or rapid immunological or DNA-based diagnostics. Air sampling is also a good way to monitor an entire population of a pathogen for changes in genetic traits such as fungicide sensitivity or pathotype.