MODELS OF A HEAD SMUT EPIDEMIC IN ITCHGRASS: THE POTENTIAL FOR BIOCONTROL
Natural Resources Institute, Chatham Maritime, UK
Background and Objectives
Materials and Methods
To simulate the impact of head smut on an itchgrass population in a naturally developing epidemic, the pathogen population dynamics (highly simplified) were also incorporated into a model of itchgrass population dynamics. The proportion of itchgrass plants infected each year was calculated, assuming that infection results from random contact between germinating weed seeds and the pathogen. The number of new smut propagules was dependant on the number of itchgrass plants infected.Results and Conclusions
The model suggested that the smut may be a useful control in combination with a cover crop. The smut will interact best with control measures which also decrease itchgrass germination, seedling mortality, seed production and proportion of the seed rain incorporated into the soil. According to the model, the smut caused a greater percentage reduction in the weed density when used in addition to the cover crop than if used on its own. However, cover crops themselves may have a yield penalty which further economic cost-benefit models of itchgrass control could be used to investigate.
Sensitivity analyses of the second model implied smut effectiveness is directly proportional to spore production and infectivity, and inversely proportional to spore mortality rate in the soil suggesting potential trade-offs when selecting the best smut biotypes. However, equivalent trade-offs in these parameters did not result in similar behaviour patterns leading up to equilibrium. Decreases in pathogen mortality rate in the soil resulted in a much more stable pattern of behaviour than equivalent increases in spore production rate or infectivity.
References 1. Ellison CA, Evans HC, 1995. Present status of the biological control programme for the graminaceous weed Rottboellia cochinchinensis. Proceedings of the VIII International Symposium on Biological Control of Weeds, 2-7 February 1992, Lincoln University, Canterbury, New Zealand (eds. Delfosse, ES & RR Scott). DSIR/CSIRO: Melbourne, pp 493-500.