The washout summer of 2012 helped slugs and snails retain their title of top plant pest.

Last year was bad for snail damage

Experts at the Royal Horticultural Society’s advisory service received almost twice as many enquiries about molluscs as cushion scale, the number two pest (see below).

Slugs and snails have been gardeners’ worst nightmare since 2011, when they knocked viburnum beetle off the top slot.

“The dominant feature of 2012 was the weather and this had a big impact on pest problems, said RHS principal plant health scientist Andrew Halstead.

“It was the second wettest year in the last 100 years. Pests that like damp conditions did well. Last summer, demand for slug controls, especially nematodes used as a biological control, sometimes exceeded supplies,” Andrew added.

Although not in the top 10, mosquitoes and midges had a good year, too. They benefited from pools of water and wet soil – ideal breeding sites for larvae.

Below average temperatures and rain, however, may have had some positive effects. This can reduce the mating success and development of pests, and also restrict their mobility.

Slug numbers have soared in wet weather

Horse chestnut leaf-mining moth, euonymus scale and viburnum beetle were less troublesome last summer.

Aphids and scale insects are susceptible to fungal infections that can spread in the wet, and this may have led to reduced populations.

Andrew added: “It will be interesting to see what effect the wet winter has on pest populations. Insects that overwinter underground or spend part of their lifecycle there can drown when soil is waterlogged.

“This affects pests and some beneficial insects like ground-nesting solitary bees.

“Slugs are often so abundant in gardens that some damage has to be tolerated. They can’t be totally eradicated.

“Vulnerable plants can be protected with slug pellets containing metaldehyde or ferric phosphate but there are non-chemical controls.

“A biological control specific to slugs is the microscopic nematode (Nemaslug).”

TOP 10 PESTS OF 2012

1. Slugs and snails

2. Cushion scale

3. Vine weevil

4. Ants

5. Glasshouse mealybug

6. Soft scale

7= Woolly aphid

7= Cypress aphid

9= Fuchsia gall mite

9= Lily beetle