Behind the battle lines

Ash dieback. Sudden oak death. Fireblight. Plum pox...

The Plant Reception area at RHS Garden WisleySounds scary? These are just a few of the economically important diseases facing UK trees at the moment. You may also have heard of oak processionary moth and Colorado beetle.

The horticultural trade means plants in Britain are under constant attack from pests and diseases both from the UK and abroad, and here at RHS Garden Wisley we have a role to play in reducing their impact on the gardens and the wider area. For example, in the past week we have found fungal disease on peony leaves and scale insect on a Neopanax.

Wisley’s propagation unit produces some 100,000 plants a year for the gardens but, like any keen gardener, our staff enjoy shopping for new ones too. The propagation unit has a plant reception area, where new plants are checked over for signs of infection or infestation. This area is closed to visitors and even garden staff can only enter with permission; this minimises the chance of disease entering the area. We have recently added signage to help our horticultural staff to recognise the most common pests and diseases, and we also encourage them to check plants carefully before buying.

A sample of a diseased plant packaged ready to be sent for testingThe vast majority of plants are from reputable growers and therefore healthy and ready to be planted out after a short period, but occasionally we see something that makes us get our magnifying glasses out and say “ooh, what’s that?” Then it’s time to involve our diagnostic teams: either pathology for diseases or entomology for insect pests. They advise us on what to do next - keep it (and keep an eye on it), compost it or burn it. We can’t be sentimental unfortunately!

How long we keep a plant in reception is usually down to the life cycle of a pest or a disease – some are slow, some are fast. We have guidelines for certain types of plants – trees and shrubs are often more prone to the nastier diseases, and so we keep these for longer. A nursery might have sprayed its plants recently, and so several months may pass before a problem becomes apparent. Certain times of year are known to be hotspots for a particular pest, so we know what to expect when, and make preparations or take precautions accordingly.

Some pests and diseases keep themselves well hidden – how many times have you seen a potted plant suddenly wilt and die back, and a quick inspection of the rootball shows little white grubs? The dreaded vine weevil is one of those where often it’s too late to do anything by the time the plant shows it is suffering. We are no more immune to these pests than the average gardener, so if you sometimes feel like everything’s out to get your plants, take heart that we too are doing battle with nefarious beasties.

Once the plants have been treated and are ‘healthy’, we release them for planting in the garden and for our visitors to enjoy.

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The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.