8 October 2026

Watch out for pest problems in the winter – top 10 winter pests

As temperatures drop, pest activity may slow, but plants / crops can still suffer from pests especially in greenhouses / conservatories and in our houses. Regular monitoring, good crop hygiene and the right biological controls can help prevent problems becoming established. Our top winter pests are :-

Sciarid Fly – Also known as compost fly / fungus gnat, Sciarid fly is a common pest of greenhouse plants and houseplants and is responsible for those tiny annoying flies in our houses. Female fungus gnats lay 50 – 300 eggs each in moist soil and it takes 28 days from egg to larva and pupa to adult, so numbers tend to build up slowly, but can then quickly get out of control. The Sciarid flies crawl over the compost surface and if disturbed fly on to the lower leaves – they can be very annoying especially on houseplants. The larval stage in the compost attacks the roots and can kill young seedlings. Control sciarid fly naturally by applying Sciarid Nematodes or use Hypoaspis on plants that you prefer not to water. It is also a good idea to position Pot Glue Traps in affected plants to catch the adults as well. 

Thrip – Thrip attacks plants damaging growing points and causing mottling, distortion and blistering of leaves. On cucumbers the fruit becomes small and twisted. Thrips will lay up to 100 eggs on the young leaves or in flower buds of plants. Once the eggs hatch, the nymphs as well as the adults feed by sucking sap. The life cycle varies and is affected by temperature, but thrip in glasshouses can breed throughout the year. Thrip can also survive out of doors all year round, but become more of a problem during hot summers attacking garden plants in sheltered situations, especially Viburnum tinus. Control Thrip underglass by applying the Amblyseius Cucumeris predator, which feeds on the larval and pupal stages of thrip or use Thrip Nematodes BOTH indoors and underglass.

Spider Mites – Spider mites can remain active in heated greenhouses and conservatories all year round, so watch out for mottled, yellowing of leaves and webbing. The females will overwinter in unheated protected structures, so it’s a good idea to use a predator late / early in the season to target these overwintering pests. Control spider mite in the autumn, spring or during cooler months, using Amblyseius andersoni as it is more tolerant of cooler temperatures.

Aphids – Aphids can remain active on protected crops in heated greenhouses / conservatories and on houseplants throughout the cooler months, causing distorted growth, curled leaves and sticky honeydew. This sticky honeydew is often the first sign of an aphid attack – the aphids excrete excess sap that drips down onto lower leaves / floor under the plant turning them sticky. Control aphids in conservatories / greenhouses by introducing Aphidius or an Aphid Predator Mix. Aphids in sheltered gardens / outdoors or heavy infestations in polytunnels / large greenhouses can be controlled using Lacewing larvae.

Mealy Bug – Mealy Bug is a major pest in conservatories and greenhouses and with more and more ornamental plants being grown in permanent plantings, this allows the pest to flourish and overwinter. Mealy Bugs are white, soft bodied pests about 5mm long. They are covered with white waxy threads and a waxy covering. Mealy Bugs feed by sucking the sap from the plant, so they will normally be found on the stems or leaf joints although they will attack leaves causing them to yellow. The insect extracts large amounts of sap with the excess sap being excreted as honeydew causing a sticky deposit on the lower leaves. Another sure sign of a mealy bug infestation is “white wool” developing on the plant leaves and stems. Control mealy bug in your greenhouse or conservatory by introducing Cryptolaemus AS SOON as you see mealy bug and the temp is 16°C/61°F.

Vine Weevil – Adult vine weevils feed on plant foliage taking distinctive “U” shaped notches from the edge of the leaf. It’s the vine weevil grubs that are the real problem, attacking the roots of plants. The grubs over-winter in the roots and emerge as adults in late spring / summer. These adults lay eggs in the root balls of plants. The eggs hatch and feed before over-wintering and then the whole process starts again. Vine weevil grubs grow to about 1cm and are creamy coloured and crescent shaped with an orange head. Affected plants will wilt even though the soil/compost is moist and as more of the roots are destroyed the plant will eventually topple over. Control vine weevils naturally by applying Nemasys® Vine Weevil Killer ALL YEAR ROUND under glass or in sheltered gardens OR use OUTDOORS between March and October. Treat as soon as you discover grubs and the soil temp is 5°c or when the grubs are at their most destructive i.e. in the spring and autumn.

Scale – Scale insect is difficult to spot, so look out for the symptoms of an attack i.e. sticky lower leaves, sooty mould and yellowing of top leaves. Outside, keep a close watch on camellias, rhododendrons, azaleas and box. Underglass, scale is very particular to all types of citrus. There are a number of different species of scale, although they are all similar in appearance and they are unlike any other pest as they don’t look alive at all! Scale insects are motionless and are stuck firmly to the stem and the underside of leaves (often around the veins) from which they suck the sap. They are dome shaped, about 0.6cm fully grown, light brown when young but gradually darken as they mature. They feed on the sap of the plant, leading to a yellowing of the leaves and in extreme cases total defoliation. Scale insects produce large quantities of honey dew which drips onto the lower leaves. Initially clear and sticky, it is then colonized by sooty mould, which is unsightly and reduces the ability of the plant to produce food, leading to further weakness and loss of vigour. This mould and honeydew are the first signs of an attack. Control Scale by spraying with Sb Invigorator Spray and / or applying Scale Nematodes.

Fuchsia Gall Mite – Fuchsia gall mite is a microscopic sap-sucking pest that causes extensive damage to the growing tips of the plants affecting the appearance of fuchsias. These tiny pest mites cannot be seen with the naked eye, but their effects on the plants are easily spotted – look out for distorted foliage, galling and will be unable to flower. The gall mites suck the sap from the shoot tips, which prevents the normal development of leaves and flowers and as the number of mites rise, the foliage becomes increasingly distorted until plants no longer produce normal leaves or flowers. Control Fuchsia Gall Mite by introducing a predatory mite called Amblyseius Andersoni that will feed on the Fuchsia Gall Mite – it can be introduced anytime between March and October or used under-glass all year round. If you are over-wintering your fuchsias in a greenhouse, then introduce the Amblyseius Andersoni once you have moved them under glass to target any gall mites still active and to protect the plants during the winter.

Whitefly – More common during the growing season, but it is easy to bring whitefly indoors on plants that you over-winter under glass i.e. pelargoniums. Adult whitefly are small, white, waxy-winged insects which congregate at the top of the plant, but fly off if disturbed. Both the adults and larval stages of the whitefly suck sap from the leaves resulting in stunted growth and damaged leaves. The sap contains excess sugar which is excreted by the whitefly and coats the lower leaves. Mould then develops, which is unsightly and produces poor growth. To control whitefly introduce Encarsia as long as the daytime temperature averages 10°C / 50°F and the whitefly are present.

Good crop hygiene – Keeping greenhouses and conservatories clean and practising good hygiene is one of the best ways to prevent pest infestations in the winter and our range of Natural Sprays and Fumigators are ideal. Use a Garlic Candle to fumigate greenhouses after the summer season and before you move all your valuable plants in for the winter to kill any pests that have survived from the summer. Cleaning greenhouses i.e. racks, staging, pots, glass etc with a Horticultural Disinfectant will remove over-wintering pests, fungal spores and the cleaner your glass is, the more light you will let in. Finally a natural spray like SB Invigorator is essential for “nipping” any pest problems in the bud or for treating pests if temperatures are too low for a predator to be used. Being chemical free, using SB Invigorator to keep pests under control during cold weather means that as soon as temperatures rise you don’t have to wait to introduce predators.

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