Type: Pests


Whitefly (Trialeurodes vaporariorum and Aleyrodes proletella)

Two closely related species of small (a few mm long), white insect insects, Trialeurodes vaporariorum and Aleyrodes proletella affect greenhouse plants and brassicas respectively. Greenhouse whitefly are all white, brassica whitefly have a dark spot on each wing. They are often present in huge numbers with clouds flying up when leaves are brushed. They feed on the sap of the plant but this is rarely enough to seriously affect the plant. Instead, the young whitefly (scales) on the undersides of leaves, and their moulted skins, make leaves look unappetising. They also excrete honeydew which attracts sooty moulds. As well as looking bad, these can reduce the amount of light getting to leaves, decreasing photosynthesis and thus growth. However, their most damaging affect is through the transmission of diseases such as various mosaic viruses and leaf curl.

Symptoms

  • Scales on the undersides of leaves
  • Clouds of white flies which fly up when disturbed
  • Sooty moulds on the top sides of leaves

Prevention & control

  • Try to prevent them moving from crop to crop across seasons by having a host-free period...although this is obviously difficult on allotments
  • Commercially available sticky yellow traps may be enough to control them in the greenhouse but, failing that, act as an early warning that further action is needed.
  • Crops which are growing strongly and have not been over-fed on nitrogenous fertilisers (which encourage weaker, sappy growth), can withstand serious attacks
  • Options for dealing with them include:
    • removing leaves from on which the young whitefly have not yet turned into the flying adults
    • vacuuming them up when they fly up having been disturbed
    • washing with insecticidal soap
    • in the greenhouse, biological control with a parasitic wasp (Encarsia formosa)
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White fly (dan - 17:00 26/01/2015) Report inappropriate tip
If you have a liquidiser blend three garlic cloves up with some warm water. pour into spray bottle spray effected plants.
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Carrot fly prevention (Roys - 11:49 21/01/2015) Report inappropriate tip
As an alternative to onions plant marigolds around your carrots to ward off the carrot fly. They also attract bees. I have also planted marigolds in my greenhouse to help with whitefly on my chillies. Since using these in my greenhouse I have not had any yet my allotment neighbour had many on his. This year I am providing my neighbour with marigolds!
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