Assessment of upward movement of rain splash using a fluorescent tracer method and its application to the epidemiology of cereal pathogens

To help understand inoculum transport in splash-dispersed cereal pathogens, the pattern and extent of upward movement of splash droplets produced by rain was measured using a 'splashmeter'. This comprised a cylinder of chromatography paper arranged vertically at the centre of an annular reservoir containing UV-fluorescent cellulose-binding dye. Natural rainfall from April to August 1985 was examined over grass and, latterly, in a wheat crop; artificial rain generated in a rain tower was used for controlled experiments. The decay in proportion of droplets reaching a given height corrected to equivalent receptor areas was exponential above 5–10 cm. The height at which equivalent areas of receptor were covered with dye was strongly dependent on the drop size spectrum of the incident rainfall, rising when larger drops were present. Presumably because of this, the results show that splash height could not be predicted from data on rainfall volume rate alone. Field observations suggested that a sudden outbreak of Septoria tritici lesions in a wheat crop could be related to unusually great upward transport of rain splash detected 3 weeks earlier by the splashmeter.