A model of the population dynamics of healthy weed plants, weed seeds in the soil, pathogen-infected weed plants and pathogen spores in the soil, was devised to investigate interactions that are important for the success of biocontrol with pathogens that prevent seed set. Three particular features of the host-pathogen interaction were examined in detail: the form of the density dependent relationship which determined seed and spore production, the host life stage at which infection could occur, and the relative competitive abilities of healthy and infected host plants. It was found that, when both weed and pathogen coexist, the equilibrium abundance of the weed in the presence of the pathogen was independent of the form of the relationship between plant density and seed or spore production. However, the form of this relationship did affect estimated equilibrium densities in the absence of biocontrol, and also affected the parametrizations under which both host and pathogen could coexist. Parameters derived from experiments with isolated host plants may therefore be sufficient to assess the biocontrol potential of new pathogens along with knowledge of densities achievable when the weed is uncontrolled. The form of the relationship used to control seed and spore production also had a marked influence on the range of parameter values over which the pathogen could persist. Other control measures were represented by changes to appropriate parameter values, e.g. weeding was represented by a change in weed death rate. With one exception, the use of additional control measures was not antagonistic to biocontrol. Often, however, the combined effect was less than additive, and the existence of synergy (where the combined effects are more than additive) was critically dependent on the form of the relationship of the rate of seed production per plant with density and the efficiency of the other control measures.
Smith, M.C.; Holt, J. Analytical models of weed biocontrol with sterilizing fungi: the consequences of differences in weed and pathogen life-histories. Plant Pathology (1997) 46 (3) 306-319. [DOI: 10.1046/j.1365-3059.1997.d01-26.x]