Here in the Botanic Garden we constantly monitor our collections for the first signs of damage. On a very basic level we strive to ensure accessions aren’t under threat from weeds, but we also monitor the threat of damage from a host of pests and disease, including wildlife. This is always a careful balancing act – nurturing and developing our collections, encouraging biodiversity, and being as sustainable as possible.
In the Glasshouses we have used an Integrated Pest Management System (IPM) for many years. This enables us to significantly reduce our use of chemicals and to manage the Glasshouse collections in an environmentally friendly way. The IPM system involves constant monitoring of our plants for the first signs of harmful pests and diseases. Common problems here include aphids, red spider mite and mealy bug, and less common problems include glasshouse thrip and soft scale. To manage these we introduce a range of predators, each specific to a particular pest. The predators act to control, rather than eradicate, populations of the pests. Visitors to the Garden may spot small sachets containing the introduced predator attached to plants in the Glasshouses.
We also experience threats to the living collection and landscape out in the Garden, where we may not have the same level of control as we do under glass. Outside in the Garden we prefer to rely on good horticultural practice and natural methods to control pests and diseases. Our horticulturists may pick damaging rosemary beetle from rosemary plants, but we usually rely on predators such as birds and ladybirds to eat pests such as aphids. Chafer grubs that have recently infested our lawns are a favourite with predating badgers and crows, which rip up the lawns to find the grubs. To treat this problem we apply nematodes to the lawns which kill off the chafer grubs, and remove temptation from the damaging badgers and crows. As in any garden we experience problems with birds eating newly sown seed, and install whistling tape to deter scavenging birds from devastating sowings.
As a green space in the City, the Garden provides a natural habitat for a number of mammals, and we have populations of badgers, muntjac, squirrels, foxes and occasional rabbits. Our squirrel and rabbit populations are monitored regularly, and in the last two decades numbers of these have levelled off naturally, and subsequent plant damage is limited. Badgers set up home here a decade or so ago and require constant monitoring as they not only cause damage to lawns, but also to infrastructure when digging out setts. They also have a habit of digging up freshly planted material in their search for food. We have found that spraying citronella can deter badgers from certain areas and plantings, though with limited success. Badgers are protected species, so we are constantly working with relevant ecological consultants to monitor populations and activity. In recent years damage by grazing muntjac has increased, with particular favourites including dogwoods in the Winter Garden, roses in the Rose Garden and our National Collections of Tulipa and Bergenia. We have installed mesh barriers around collections favoured by muntjac and badger, although this detracts from the plantings themselves. In addition we operate a programme of active boundary management and clearance to limit access and cover for muntjac.
We are also conscious of the threats posed by devastating pests and diseases, including ash dieback (which is responsible for the death of native ash in the UK), oak processionary moth (which results in oak trees being stripped of their foliage, making them more vulnerable to other threats e.g. drought), Xylella (a bacterial disease which has decimated swathes of olive groves in southern Italy), and box blight (an unsightly fungal disease which damages foliage and weakens plants). To minimise the impacts of such threats, the Garden is constantly monitoring existing plantings and incoming plant material to ensure that we can act on any such threats at the earliest opportunity.