A model to determine the potential for biological control of Rottboellia cochinchinensis with the head smut Sporisorium ophiuri.
A difference equation model of the population dynamics of R. cochinchinensis was developed for a maize cropping system. The model was used to estimate the constant annual infection rate by S. ophiuri that would be necessary to provide long-term control of the weed. The model suggested that, with the smut as the sole control agent, an annual infection rate of about 88% would be required to reduce R. cochinchinensis density to 10% of the level achieved with no control. However, when combined with one or two weedings per year, the level of infection necessary for satisfactory control could be reduced. Since the maximum infection rate achieved in experiments was about 80%, the smut was unlikely to achieve satisfactory control when used alone, but the results suggested that S. ophiuri could be a useful adjunct in integrated control programmes. The extent to which the effectiveness of the smut was improved by combining it with weeding depended on the seed set in the R. cochinchinensis flush emerging after weeding and on seedling mortality. Where seed set or seedling survival were low, the required infection rate could be substantially reduced. The results are discussed in the context of future prospects for biological control of R. cochinchinensis, and areas for further research to improve the utility of the population dynamic model are highlighted.