How to get rid of garden pests and treat plant diseases in the UK

Pests and diseases can plague gardens relentlessly by causing damage all year round – affecting seedlings, spoiling ornamental plants and rotting vegetables. 

The Royal Horticultural Society are often asked for advice from gardeners who continue to battle familiar foes. Among the most frequent concerns are worries about the impact of disease on a plant’s appearance including mildew on flowering cherry, rust on pear, blackspot on roses and glasshouse red spider mite. 

The UK’s number one plant disease, honey fungus, has topped the disease ranking for a quarter of a century. Famed as the ‘silent killer’, the fungus attacks a large number of woody and perennial plants and spreads underground, attacking roots and decaying bark.

And slugs and snails are often behind damage to crops like potatoes, beans and border plants, including clematis and hosta.

Andrew Salisbury, Principal Entomologist at the RHS, says: “The pests and diseases that gardeners commonly face on their plots has fluctuated over the last 25 years but some age-old problems persist.

“With gardens taking on a more important role in supporting wellbeing and the environment it’s important that research into management and mitigation of them continues.” 

Below, we’ve listed the top six that cause issues for gardeners and the best ways to tackle them. 

Most common garden pests and plant disease

Honey fungus 

The UK’s most common plant disease, honey fungus is spread via rhizomorphs (black “horsehairs” or “bootlaces”) that travel from the dead wood of host trees and shrubs, unseen underground in the top 18in (45cm) or so of soil.

Plants most at risk are those under stress – from old age, drought or waterlogging – and, sometimes, the first symptom you’ll notice is the death of the tree or shrub. Severe infection can cause plants to ‘bleed’ or the bark to split just above ground level. 

Although honey fungus can produce honey-coloured toadstools in late summer and autumn, they don’t always appear even if infection is present. Look out for their collar-like rings and creamy white gills.

The RHS suggests that in order to diagnose honey fungus, gardeners should peel back the bark on the roots or base of the affected plant to see the inner tissue; here, you’ll notice a white layer of paper-thin fungal tissue that smells of mushrooms. 

Experts advise that gardeners do not replant infected spaces for at least a year to starve out the fungus. When replanting, an 18in (45cm) vertical barrier using butyl rubber pond liner, for example, around new and special plants has proved to be effective. 

Be aware that there are no chemicals to control honey fungus. As soon as you spot a diseased plant, dig it up with as many roots as possible and remove from the garden.

Slugs and snails 

Young plants are particularly vulnerable to slug and snail attack and it is important to protect seedlings. Here are some of the best products for dealing with these long standing enemies – many of which are available from more than one retailer. 

GrowAid Slug Gone (3.5 litres for £8.90; amazon.co.uk)

These non-toxic pellets are made from concentrated sheep’s wool which irritates the slugs when they slide over it. Helen Yemm’s favourite slug beater, suitable for organic gardening.

Slug Barrier Tape (4m for £4.99; capitalgardens.co.uk)

Adhesive copper tape designed to protect pot plants. When slugs and snails slide onto copper, they get a mild electric shock and retreat. Simply stick in place around the rims of your pots.

Nemaslug  (£13.87 for 40 sqm; amazon.co.uk)

Nemaslug saturates your soil with the nematode Phasmarhabditis hermaphrodita – 300,000 of them per square metre. These microscopic worms infect slug brains, but leave birds and other predators unaffected.

Vine weevil