Biological control of three Eupatorieae weeds in South Africa: 2011-2020.
Several weed species within the asteraceous tribe Eupatorieae, all with a neotropical origin, are invasive in South Africa. Three of these form the subject of this review paper: Chromolaena odorata (triffid weed), Campuloclinium macrocephalum (pompom weed), and Ageratina adenophora (crofton weed). The three species invade different habitats and regions, and all have biological control (biocontrol) agents established on them. Ageratina adenophora was the first of these weeds to be subjected to a biocontrol programme in South Africa, with two agents (an insect and a pathogen) released and established in the 1980s. Two biocontrol agents were established on C. odorata in the early 2000s, and a third one, first released in 2011, has persisted for at least eight years - all three are insects. One insect biocontrol agent was established on C. macrocephalum in 2013, although a pathogen had appeared on the weed several years earlier. Chromolaena odorata and A. adenophora are under substantial control in certain habitats, but negligible in others. The biocontrol agent on C. macrocephalum released in 2013 is causing significant damage to the plant where it has established well. Several other biocontrol agents have been released on C. odorata but have failed to establish. For all three weedy Eupatorieae, it is considered desirable to establish additional biocontrol agents, so as to increase the level of control of these priority targets in South Africa. An additional biocontrol agent has already been approved for release against C. macrocephalum, while one is close to being approved for C. odorata. There are several possibilities for additional biocontrol agents for A. adenophora.