Spores Are Ballistic, Not Wind-Borne

01The evidence

• Ballistospore discharge in Itersonilia perplexans has been characterised as a surface-tension-driven process, with the spore launched by the coalescence of a drop rather than by air movement.Mycological Research

02The tension

Dispersal is modelled as a passive process: spores are released and transported by air, so wind speed and turbulence set the range. That model underpins disease forecasting, and it systematically fails to predict the short-range clustering that is observed in outbreaks.

03The theory

The launch is powered by the surface energy of a drop that coalesces on the spore, and the energy release is fast enough to accelerate the spore to a significant velocity. The initial trajectory is therefore set by the geometry of the launch apparatus, not by the air.

The wind then acts on a spore that already has momentum and direction. That makes dispersal a two-stage process: a deterministic launch followed by stochastic transport. The short-range pattern is set by the first stage, which is why it is clustered.

The prediction is that humidity should control the launch, because the mechanism depends on condensation, and that launch distance should be predictable from the size of the drop. It also predicts that wind speed should matter less for short-range clustering than expected.

The applied consequence is that disease forecasting should include humidity-driven launch probability, and that spatial models should use a launch kernel rather than a diffusion kernel.

04What this is not

05Predictions

• P1Spore launch distance should be predictable from drop size and geometry rather than from wind.
• P2Humidity should control launch probability more strongly than wind speed.
• P3Short-range clustering should follow a launch kernel rather than a diffusion kernel.

06What would refute it

Dispersal patterns explained by wind alone, with launch contributing nothing, would restore the passive model.

07What it would change

It would change disease forecasting and the spatial modelling of fungal outbreaks.