Disease epidemics and plant competition: control of Senecio vulgaris with Puccinia lagenophorae

Abstract

One approach to biological control of weeds is to relieve competition between crop and weed by inducing and stimulating epidemics of a pathogen on the weed. Results of a field experiment in Switzerland suggested that an epidemic of the rust fungus Puccinia lagenophorae could reduce losses in the crop celeriac (Apium graveolens) caused by competition with the annual weed Senecio vulgaris. Size hierarchy of celeriac increased in the presence of S. vulgaris and increased further by induction of a P. lagenophorae epidemic. The latter increase in size hierarchy could be explained by the spatial dynamics of the P. lagenophorae epidemic on S. vulgaris. Plants in the vicinity of the inoculum sources were infected earlier and more heavily than plants farther away causing variation in the impact of the pathogen on competition between celeriac and S. vulgaris. A positive relationship between infection of S. vulgaris by P. lagenophorae and celeriac yield could be observed. The study yielded insight into the impact of a disease epidemic on the competitive balance between two plant species and the results can be used to validate calculations about the number and spatial distribution of inoculum sources of P. lagenophorae required to control a S. vulgaris population.