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Pests & Problems Part 5 - Whitefly

If you grow chillies, you can be pretty sure you will run into the problem of Whitefly sometime in the future.  These sap sucking pests affect indoor and greenhouse plants. Controls vary, depending on the number and location of your plants.

Whitefly adults and larvae

Whitefly are moth like insects with white wings which grow up to 2mm in length.  They breed extremely quickly and affected plants will seem to have a white-cloud caused by the sheer numbers of pests swarming around. Female adults lay around 200 eggs on the underside of leaves, often in a circular groups.  They are a problem you need to address as these critters not only attack your chilli plants but also peppers, tomatoes, cucumbers and many ornamentals.

They thrive in sunny conditions and we tend to find they are a problem at the end of the growing season whereas greenfly/aphids tend to be a problem at the start of the season.Whitefly

The species we are specifically referring to is Glasshouse Whitefly or "Trialeurodes vaporariorum". Cabbage Whitefly "Aleyrodes proletella" are different.  These are similar to glasshouse whitefly, but they have grey spots in the centre of each wing and attack only cabbages and other brassicas.

They are sap-sucking insects and excrete the sticky excess, called Honeydew, onto lower leaves where it encourages black sooty mould to grow. This mould stops the leaves from receiving sunlight, so they are unable to manufacture food via photosynthesis. 


Symptoms 
  • Yellowing and disfigured leaves caused by whitefly feeding on the plant cells.
  • Swarms of small white insects appearing around your plants when the leaves are disturbed.
  • Black sooty mould deposits forming on leaves
  • On the underside of leaves, it is easy to spot the Whitefly eggs and scales.

Control

Whitefly do have a reputation for being difficult to control.    

We do not use YELLOW TRAPS.  These are sticky cards which are hung up around plants and attract insects to their sticky surface. Once stuck, they cannot move.  Yellow traps are only good for one purpose in our opinion and that is to alert the gardener to a potential problem with their plants such as whitefly or aphid attack.  The major drawback with these traps and the main reason we do NOT use  them is that you are very likely to catch and kill the good predators aswell, the ones you want in your greenhouse.


Biological ControlEncarsia formosa

If you are growing your chillies in a greenhouse or polytunnel you can use a biological control called "Encarsia formosa". This is a parasitic wasp which which lays its eggs in the scales where the larvae develop and so kill the nymph. The larvae hatch into adults, which find more scales to parasitise.     It is important to introduce the parasite before plants are heavily infested as it cannot give instant control. Parasitised nymphs turn black so they are easy to spot. Encarsia need a temperature of around 18°C to survive, and will die out when all the whitefly have gone, so you may need several introductions throughout the season.


Companion Planting 

We grow Basil, Mint, Nasturtiums and Pot Marigold in our tunnels.  Although there is no scientific proof, we have not experienced significant problems with whitefly in all years we have been growing chillies.  Companion planting is a brilliant way of attracting the good predators into your growing environment.


Other controls 
  • Handpick older leaves to remove young whitefly stages. If you have used Encarsia formosa, make sure not to remove leaves with black dots (as these are likely to be the larvae of the predator wasp)
  • There are lots of sprays available. We have heard good things about SB Invigorator which is an environmentally friendly insecticide which can be used to control Whitefly, Aphid, Spider Mite and Mealybug attack.
  • Using a nettle feed on your plants will attract good predators into your greenhouse such as Ladybirds and Lacewings. These beneficial predators love eating Whitefly adults and their eggs.
  • Organic sprays which contain fatty acids and plant oils are a good deterrent.  We've heard good things about Savona Fatty Acid Concentrate.
  • Dilute 1 capful of washing up liquid into a water spray gun and spray this onto your affected chilli plants.  This is a good method for indoor plants where biological controls are harder to apply. If you do not wish to use washing up liquid then a spray made with infused rhubarb leaves or crushed garlic is a good alternative.  We have heard from one chilli grower who swears by infusing hot chillies in water and using this on whitefly larvae (a test for the future we think!)
  • If you have plants indoors, we recommend placing them outside in a sunny position on a summers day. You will be surprised with the difference this makes.  Passing beneficial predators such as hoverflies will consume numerous amounts of whitefly without any real effort from you!
  • Hang birdfeeders around your garden. So simple but this will attract insect eating birds into your growing environment.
  • Avoid using a lot of nitrogen fertilizer, including manures, as succulent growth will increase whitefly populations.
  • You can cover your plants with horticultural fleece to stop whitefly attacking them. Unfortunately this doesn't look to great! 
  • We know of at least one gardener who uses a hand-held car vacuum to suck up the clouds of whitefly adults and eggs from their chilli plants!      This is a good idea if you have indoor plants.  Once trapped, bag the little suckers and freeze for 24 hours.

Prevention
  • Check plants every day for signs of infestation and deal with them as soon as they appear. Remove leaves with large infestations of whitefly larvae.
  • Remove all weeds/plant debris around your cultivated plants.
  • Do not use standard insecticides as this will kill off beneficial predators and all biological controls
  • Whitefly can over-winter on crops or weeds so at the end of the season, it is important to clear and disinfect your greenhouse/tunnels.