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Pests

Whitefly

  • Seen frequently in glasshouse grown crops, tiny white mothlike insects lay their eggs on the underside of leaves which hatch and develop into larvae which suck sap and can also transmit viral diseases.
  • Feeding larvae also secrete honeydew which attracts nuisance insects like wasps and can lead to the development of sooty moulds.
  • Strict hygiene can keep your greenhouse free of this pest. Completely clean down and remove any plant debris from previous crops during the winter season, including any weeds.
  • Thoroughly inspect any plant material brought into the glasshouse paying particular attention to the undersides of leaves.
  • Spraying with soap solution may make life difficult for this pest. If the pest becomes a major problem your local garden centre or garden shop may have some specific control products available. (Follow manufacturer’s directions and safety instructions.)

Biological option

  • You can now purchase a predatory wasp, Encarsia formosa, from a garden centre or online. This wasp lays its eggs in whitefly eggs, thus reducing the numbers of emerging whitefly.
  • Sprays based on organic fatty acids and vegetable oils work by smothering the insect.
  • ‘Sticky Traps’ will also help to keep populations low.

Companion Planting

There is some evidence that planting marigold plants at the base of tomatoes can help reduce whitefly infestation of tomato plants.


Aphids (Green Fly)

  • Green, black, red, woolly or waxy, these sap sucking insects feed on the young growth and under leaves causing distortion and weakening the plants.
  • Aphids can also carry virus diseases.
  • Soft soap solutions upset the insect’s ability to cling to plant. If the pest becomes a major problem your local garden centre or garden shop may have some specific control products available. (Follow manufacturer’s directions and safety instructions.)

Biological option

  • You can now purchase a parasitic wasp, Aphidius, which uses its ovipositor to lay eggs within immature aphids.
  • Ladybirds, particularly their larvae, are significant predators of aphids. Lacewings are also effective in controlling aphids.

Companion Planting

Hoverflies also feed on aphids. To attract them towards your crop plant flowers such as dill, fennel, daises, cornflowers and buckwheat.


Red Spider Mites

  • These tiny mites, present on the undersides of the leaves, are difficult to spot and may first be seen when the sucking damage they cause shows up on the upper surface of the leaves as yellow speckling.
  • They will weaken the plant by sucking the sap and when present in large population mature mites will create webbing.
  • Completely clean down and remove any plant debris from previous crops during the winter season. Thoroughly inspect any plant material brought into the glasshouse paying particular attention to the undersides of leaves.
  • If the pest becomes a major problem your local garden centre or garden shop may have some specific control products available. (Follow manufacturer’s directions and safety instructions.)

Biological option

A number of predatory mites, Phytoseiulus spp. or Amblyseius spp. are now available and are excellent at controlling red spider mite populations as long as they are added before the pest population becomes too high. If the pest population is high before adding the predatory mites, treat with fatty acid oil before introducing the predatory mites.


Sciarid Flies

  • These small black flies occur frequently when using peat and green-waste composts.
  • Their larval stage, small clear bodied larvae with shiny black heads, feed on fungi in the growing media and will tunnel into the base of the stem of weaker seedlings.
  • The adults can be an annoyance in the greenhouse, but also they can spread disease on their legs around the house.
  • Their presence can be an indication of over-watering.
  • Sticky traps can help keep the adult numbers down (Yellow Traps).

Biological option

A predatory mite, Hypoaspis miles is now available and eats the larvae. It is best to apply this mite on the surface of the growing media rather than in the plant canopy. You can also use a nematode, Steinernema feltiae, which again attacks the larval stage.