Effects of rainfall intensity and duration on dispersal of Rhynchosporium secalis conidia from infected barley leaves

Simulated rain of two intensities was allowed to fall for 30 min on to barley leaves infected by Rhynchosporium secalis. The resulting splash droplets were collected on horizontal pieces of fixed photographic film. Most spore-carrying droplets were in the 400–800 μm diam range. They were dispersed as far as 1 m from the barley leaves and the number of conidia collected on horizontal microscope slides declined exponentially with distance from the leaves. It was estimated that, of the conidia dispersed in 30 min of simulated rainfall with an intensity of 12 mm h⁻¹, 40% were dispersed in the first 10 min and 27% in the last 10 min, and with an intensity of 65 mm h⁻¹ 39% were dispersed in the first 10 min and 25% in the last 10 min.
Horizontal pieces of film and microscope slides were placed, under rain-shields, at 15 cm above ground level in an infected crop of winter barley during June and July 1985. Of the spore-carrying droplets collected during periods of rain, most were less than 400 μm diam, but most spores were in 400–800 μm diam droplets. No conidia were collected during dry weather or during rainfall with intensity less than 0.2 mm h⁻¹. During showers most conidia were collected when rainfall intensity was greatest; a regression of number of conidia collected cm⁻² min⁻¹ on rainfall intensity (both square-root transformed) accounted for 76% of the variance.