Splash dispersal of fungus spores and fungicides in the laboratory and greenhouse

A laboratory technique is described for the production of drops of simulated rain in which fungal spores were suspended. When such drops containing conidia of Botrytis fabae impacted on a target leaf the secondary droplets produced infections on receptor broad bean leaves. The capacity of fungicides applied to the target leaf to redistribute in secondary splash droplets was examined in terms of the infectivity of the spores in the droplets. The extent to which a copper fungicide reduced infection on the receptor leaves was related to the level and tenacity of the fungicide deposit on the target leaf. The effect of wetting agents on the redistribution of this fungicide could probably be explained by their influence on the tenacity of the initial deposit. In general the capacity of different fungicides to inhibit infection by the secondary droplets was related to the inherent toxicity of the fungicides to B. fabae. Implications of the dispersal of spores and fungicides by rain splash are briefly considered with reference to field conditions.