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The Bug Files: Know the enemy attacking your greenhouse

There’s a titanic battle going on in your greenhouse.

While your pretty plants are popping up, pesky pests are ready to take them down. From weevils to whitefly – everyone’s looking for a slice of your harvest; nibbling leaves, sucking sap and causing a general all-round nuisance.

Fear not, we’ve got the lowdown on the perpetrators, and how to fight back…

Red Spider Mites

Distinguishing features: Reddish brown colouring, 0.5-0.7 mm in length

Whereabouts: Underside of leaves

Crimes: Attacks on foliage – causing a mottled appearance and, in severe cases, plant death. Strikes on a wide range of greenhouse plants including peaches, cucumbers and tomatoes, and many ornamentals including fuchsias and pelargoniums.

How to take them down: Damp down your greenhouse regularly during summer to raise humidity. Avoid growing susceptible plants. Regularly spray with a fine mist of water. Any way you can increase greenhouse humidity levels helps.

Whitefly

Distinguishing features: Tiny, pure white insects which lay white eggs

Whereabouts: Underside of leaves

Crimes: Sucking sap from the leaf undersides of tomato, cucumber and many ornamental plants, causing stunted growth. Making foliage sticky by excreting a sugary substance called honeydew.

How to take them down: Suspend yellow adhesive strips above your plants – the insects are attracted to the colour and meet a sticky end.

Mealybugs

Distinguishing features: White or whitish pink, small, soft-bodied with sucking mouthparts

Whereabouts: Stems and leaf whorls

Crimes: Sap sucking, leaving sticky deposits where they feed. Infestation of inaccessible places. Cacti and succulents are common victims.

How to take them down: Check plants carefully before putting them in your greenhouse, release the ladybird Cryptolaemus montrouzieri to control them.

Vine Weevil

Distinguishing features: Creamy white, soil-borne larvae up to 10mm long. Adults are grey beetles, about 9mm long, with distinctive snout

Whereabouts: Leaves and roots

Crimes: Devouring the roots of your plants – Cyclamen, fuchsias and primulas are particularly susceptible. Night-nibbling the edges of leaves.

How to take them down: Check your plants weekly to stop infestations getting out of control. Remove and destroy newly-hatched adults to reduce the numbers of eggs laid in the soil. Use netting to stop adults moving between your plants and laying eggs in your pots.

General good greenhouse practice

  • Before sowing seeds in the spring, get rid of any dead plants, rotting leaves or weeds

  • Wash greenhouse glass with warm soapy water

  • Use clean pots, fresh compost, and tap water from a clean watering can rather than water stored in a butt

  • If you have a soil border in your greenhouse, try to grow a different crop in it each year to stop the soil building up pests and disease

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