AN EMERGING SYSTEM MANAGEMENT APPROACH FOR BIOLOGICAL WEED-CONTROL INCROPS - SENECIO-VULGARIS AS A RESEARCH MODEL

A 'system management' approach of biological weed control in crops is proposed and compared with other methods of biological weed control. I t is based on the management of a weed pathosystem in order to maximiz e the natural spread and disease severity of a native or naturalized p athogen. This approach may be well-suited to situations where it is ne cessary to control single weed species in crops, and where no immediat e and complete control is required, the production of large amounts of the agent is rather limiting (e.g. when using biotrophic fungi), and/ or the importation of an exotic agent is not possible. This strategy p rovides fundamental knowledge of underlying mechanisms of crop product ion systems and is aligned with the view of modern agro-ecology, in wh ich complete eradication of weeds is not desirable. The fundamental re search required for a successful application of the 'system management ' approach will be illustrated with the biological control project of Senecio vulgaris L. using the naturalized rust fungus Puccinia lagenop horae Cooke. A five-step procedure, together with selected results, wi ll be presented. Main emphasis is given to the infection window, the s tudy of the genetic structure of the plant and pathogen population, an d the management of the infection conditions (a) to maximize the sprea d of the disease and the impact on the plants, and (b) to minimize the development of resistant plant populations. Joint application of herb icides at low doses, additional necrotrophic pathogens, and of biochem icals interfering with the weed's defence also will be envisaged, as w ell as their integration into general pest control practices. In this regard, biological weed control agents have to be seen as stress facto rs, not as weedkillers, and biological weed control as an integral par t of a well-designed pest management strategy, not as a sole cure.