Despite impressive efforts at clearing stands of invasive Australian Acacia species in South Africa, insufficient attention has been given to understanding the role of seed banks in the invasiveness and long-term persistence of populations. We review information on seeds of these species, considering seed production, seed rain, and the dynamics of seeds in three layers: leaf litter, and upper and lower seed banks in the soil. Many factors affect the accumulation and susceptibility to destruction of seed banks and thus the opportunities for intervention to reduce seed numbers for each of these components. Reduction of seed banks is crucial for the overall success of the multi-million dollar management initiatives against these species. Classical biological control of buds, flower and young pods has reduced the seed production of many Australian acacias in South Africa. Fire can be applied to reduce seed numbers in the leaf litter and upper seed bank in some cases, although there are serious problems associated with high fire intensities in dense acacia stands. Other options, e.g. soil inversion and solarisation, exist to exercise limited reduction of seed numbers in some situations. There is little prospect of meaningful reduction of seed numbers in the lower seed bank. Preventing the accumulation of seed banks by limiting seed production through biological control is by far the most effective means, and in almost all cases the only practical means, of reducing seed numbers. This must be an integral part of management strategies. Several invasive Australian acacias are already under effective biological control, and further work to identify additional potential agents for all the currently invasive species and potentially invasive alien species is the top priority for improving the efficiency of management programmes.

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Pareuchaetes aurata aurata (Butler) from Chromolaena jujuensis in northern Argentina was tested as a biological control candidate for the composite weed C. odorata. The larvae feed voraciously and complete their development on C. odorata. The host-plant feeding range of P. a. aurata is limited to the genus Chromolaena. It is suggested that the egg-laying behaviour of P. a. aurata, which scatters its eggs around the base of the host-plant, will help to overcome the problem of ant predation which prevented the establishment of Pareuchaetes pseudoinsulata Rego Barros, which lays its eggs in batches, in South Africa. Any possible benefits of the new association between P. a. aurata and C. odorata may also contribute to the success of this biological control programme.

Four integrated control strategies were developed for wattle that could not be removed for utilization. In the first two strategies, a combination of mechanical and/or chemical control methods either reduced the wood biomass in situ (fell, stack and burn) or retained the wood biomass above the soil surface (control of standing trees). Fol-lOw-up control involved a combination of chemical control and burning high fuel loads of sown pastures species. For the third strategy, dense infestations were contained and prevented from encroaching into neighbouring veld (grasslands). These infestations were controlled once sufficient funds became available, or converted to wood lots and shelter belts. The fourth strategy descri~es control of dense seedling regeneration promoted by uncontrolled fire, and the calculation of a reserve 'fire fund'. A customized management plan was developed for a particular property that assigned these six integrated control strategies to infestations in different situations. Prioritizing the infestations allowed the optimum allocation of the available resources within a realistic time span, thereby ensuring sustained progress was made in the reduction of infestations to acceptable levels.