Role of botanic gardens for ornamental plant conservation through sustainable management: case studies at Hanbury Botanic Gardens

Botanic gardens have been collecting ornamental plants from all over the world for years; the collections represent scientific, historical, biological and genetic diversity assets. In recent years there has been an increase in parasitic infestations on many plant collections as a result of both the introduction of several alien species and climate change. To preserve plants acclimatized in these places over time and to safeguard the environment and the health of gardeners and visitors from the widespread use of synthetic substances, the management of these parasites using sustainable methods becomes a priority. The Hanbury Botanic Gardens accommodate important ornamental plant collections. The most significant, distinguished by high diversity and historical-cultural value, are those of the genus Agave, Aloe, Citrus, and the palm collection. Several parasites currently threaten their conservation: Scyphophorus acupunctatus, the agave black weevil, is controlled using an integrated pest management strategy; Aceria aloinis, an eriophyid mite that causes physiological and morphological alterations of the Aloe species, is controlled through the release of predatory mites such as Neoseiulus californicus and Amblyseius swirskii; citrus scales are controlled through the release of predators and parasitoids. The two palm parasites, the weevil Rhynchophorus ferrugineus and the moth Paysandisia archon, are controlled by using entomopathogenic products based on the fungus Beauveria bassiana and the nematode Steinernema carpocapsae. The control of these pests includes the use of monitoring techniques, good agronomic practices, and the employment of antagonistic organisms. This kind of management results in an effective and sustainable control of natural parasites that is suitable for the conservation and defence of ornamental plants. This strategy avoids the use of dangerous chemical products and is potentially applicable both in urban greenery and in private gardens