Patterns of persistence demonstrate the vulnerability of the root hemiparasite Thesium utile AWHill (Santalaceae) to weed control measures

A herbicide trial in a Highveld grassland revealed, serendipitously, a positive association between the root hemiparasite Thesium utile and the noxious weed Campuloclinium macrocephalum (pompom weed). The parasite was unable to survive in plots where the weed was selectively removed by hoeing, but persisted and increased in the untreated control. Herbicides were more effective at killing Thesium than suppressing C. macrocephalum. A host-specific rust attacking the foliage of C. macrocephalum had no impact on T. utile survival. Weed control measures against C. macrocephalum are not likely to threaten native Thesium species as they have a large range of host species. These types of interactions should be investigated further in other species to improve our understanding of the ecology of root-parasites. (c) 2022 SAAB. Published by Elsevier B.V. All rights reserved.