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What's bugging you?

PUBLISHED: 10:00 29 July 2017 | UPDATED: 12:18 31 July 2017

An adult vine weevil on a leaf

An adult vine weevil on a leaf

© RHS

Trouble with greenhouse critters munching your plants? Expert Nigel Colborn explains how to tackle the main culprits

A red spider miteA red spider mite

As crops swell and flowers bloom, our greenhouses are filling up with gorgeous plants. The only trouble is, destructive pests are also intent on moving in, uninvited.

Here gardening expert Nigel Colborn, former presenter of BBC Gardeners’ World, offers tips on how to identify and control the most troublesome greenhouse bugs.

Red spider mite

These are found on the underside of leaves where a fine web develops. They attack the foliage, causing a mottled appearance and, in severe cases, death of the plant.

They attack a wide range of greenhouse plants including peaches, cucumbers and tomatoes, and many ornamentals including fuchsias and pelargoniums. To suppress red spider mite, damp the glasshouse down regularly during summer to raise humidity. Also, try to avoid growing susceptible plants.

Whitefly

These are tiny, pure-white insects which reproduce quickly, laying white eggs on the undersides of leaves. They suck sap from the leaf undersides of tomato, cucumber and many ornamental plants, which can result in stunted growth. They also excrete a sugary substance called honeydew which makes the foliage sticky. They love warm conditions and fly up from plants when disturbed. Keep whitefly numbers down by suspending yellow adhesive strips above the plants. The insects are attracted to the colour and become attached.

Vine weevil

Often, you don’t spot vine weevil until it’s too late, by which time the soil-borne larvae will have devoured the roots of your plants. Cyclamen, fuchsias and primulas are particularly susceptible. The grubs are creamy white, up to 10mm long and feast on plant roots and tubers. Vine weevil are hard to detect, but keep a lookout for the adults, which are grey beetles, about nine millimetres long, and have a distinctive snout. They feed at night, nibbling notches around the edges of leaves.

Thrips

Also known as thunder flies, these tiny sap-sucking insects eat young plant tissue, including flower petals, causing mottling. Leaves can become dull and turn silvery-white and heavy attacks may stop flower buds from opening. Adults are yellowish brown or black with long, narrow bodies, but are often hard to detect unless you shake the plant over a piece of paper. Sticky traps can help control them.

Mealybug

The white, sap-sucking pests leave sticky deposits where they feed. Cacti and succulents are among the vulnerable plants, and the insects, which are active all year round, can infest pretty inaccessible places. Females don’t fly or crawl far so are often brought in on an infested plant. Check your plants carefully before putting them in the greenhouse. The ladybird Cryptolaemus montrouzieri, available from specialists, can be released into greenhouses to control them.

More advice

Nigel Colborn’s advice forms part of a new greenhouse guide he has written in collaboration with greenhouse specialists Hartley Botanic, available to download here.

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