Glasshouse whitefly

Glasshouse whitefly is a common sap-feeding pest, mainly of houseplants and greenhouse plants. Whiteflies excrete a sticky substance (honeydew) on foliage, which allows the growth of sooty moulds.

Glasshouse whitefly. Image: ©www.gardenworldimages.com

Quick facts

Common name Glasshouse whitefly
Scientific name Trialeurodes vaporariorum
Plants affected Many houseplants and greenhouse plants
Main symptoms Sticky honeydew on foliage, black sooty moulds, small white-winged insects
Most active All year round

What is glasshouse whitefly?

Glasshouse whitefly is a sap-sucking insect pest that reduces the vigour of plants and excretes a sticky, sugary substance, called honeydew, on the leaves, stems and fruits of its host plants.

It attacks many vegetables and ornamental plants grown in greenhouses as well as houseplants. These include: cucumber, melon, tomato, peppers, Chrysanthemum, Gerbera, Pelargonium, Fuchsia, Lantana, poinsettia and Verbena. Outdoor plants can also be attacked but not to such a damaging degree. Note that whiteflies seen on brassicas, Viburnum tinus, honeysuckle, evergreen azalea and rhododendron are other species of whitefly specific to those plants.

It thrives in warm conditions, which is why it is not usually a problem on outdoor plants. Glasshouse whitefly is active all year round on houseplants and in greenhouses.

Symptoms

You may see the following symptoms:

  • It is relatively easy to see whiteflies on infested plants, especially if a plant is disturbed, when clouds of small white-winged insects, 1.5mm (about 1/16in) long, will fly up
  • Adult whitefly and the nymphs excrete sticky honeydew on the foliage, stems and fruits, which allows the growth of black sooty moulds
  • You may also see flat, oval, creamy white scale-like nymphs on the underside of leaves

Control

Due to this pest's rapid reproductive rate and the widespread occurrence of pesticide-resistant strains, biological control often gives better results than insecticides on greenhouse plants.

Non-chemical control

Biological control

This involves introducing tiny parasitic wasps, Encarsia formosa, which attack the whitefly nymphs. The parasite is available by mail order from the suppliers of biological controls. It is important to introduce the parasite before plants are heavily infested as it cannot give instant control. Parasitised nymphs turn black so it is easy to monitor the progress of the control. As Encarsia is killed by most insecticides, avoid spraying with products other than fatty acids, urea/mineral lattice, plant extracts or plant oils (see below) prior to its introduction.

Other non-chemical controls

Hang sticky yellow sheets (widely available from garden suppliers) above or among the plants to trap adult whitefly. Glasshouse whitefly can feed and breed on weeds so good weed control inside and around the glasshouse will remove alternate host plants. Watch for signs of whitefly on new purchases as the pest is often first brought into a glasshouse on new plants. If possible quarantine new plants in order to give eggs and nymphs a chance to develop and be recognised. Good ventilation will help to check the growth of sooty moulds.

Chemical control

Frequent sprays with contact insecticides deltamethrin (e.g. Bayer Sprayday Greenfly Killer), lambda cyhalothrin (Westland Resolva Bug Killer), pyrethrins (e.g. Py Spray Garden Insect Killer, Py Bug Spray, Doff All in One Bug Spray, Bug Clear Gun for Fruit & Veg, STV Time’s Up Bug Killer, Defenders Bug Killer, Growing Success Fruit & Veg Bug Killer, Growing Success Shrub & Flower Bug Killer, Vitax House Plant Pest Killer, Pyrol Bug & Larvae Killer Concentrate), plant extracts (e.g. Vitax Organic 2 in 1 Pest & Disease Control Concentrate, Bug Clear for Fruit & Veg, Agralan Whitefly Killer), fatty acids (e.g. Bayer Organic Bug Free, Bayer Natria Bug Control, Doff Pest Spray, Doff Universal Bug Killer, Just Green Savona Concentrate, Nature's Answer Natural Fungus and Bug Killer or Greenfingers Organic Pest Spray) or urea/mineral lattice (SB Plant Invigorator) can control established infestations. Resistance to pyrethrins, deltamethrin and lambda-cyhalothrin can occur. Products containing deltamethrin and lambda-cyhalothrin can be used on edible plants listed on the label provided the label instructions on maximum dose and harvest interval are followed.

Systemic insecticides can be applied as foliar sprays or compost drenches. Systemic insecticides are absorbed into the plant tissues and are taken up by sap-sucking insects when they feed. They also usually have some contact action. There are several formulations available. 

  • A compost drench containing thiocloprid (e.g. Bayer Provado Vine Weevil Killer 2) is for application to the roots of ornamental plants growing in pots or containers only
  • Foliar sprays containing thiacloprid (e.g. Bayer Provado Ultimate Bug Killer) can be sprayed on the foliage of ornamentals and some edible plants (e.g. greenhouse-grown tomatoes, peppers, aubergine and cucumber) provided the label instructions can be applied as a compost drench (e.g. Bug Clear Ultra Vine Weevil Killer) on container-grown ornamental plants, or as a foliar spray (e.g. Bug Clear Ultra or Bug Clear Ultra Gun) on ornamental plants only  

Downloads

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biological control suppliers (Adobe Acrobat pdf document)

Biology

This sap-sucking insect pest breeds rapidly and produces many generations in warm greenhouse conditions. The adults and their whitish scale-like nymphs live on the underside of the leaves where they feed on sap, weakening the plants. They lay greyish white cylindrical eggs either singly or in circles on the underside of the leaves.

Each female can lay more than 200 eggs. Males are rare and reproduction takes place without the need for fertilization. The eggs hatch into small scale-like nymphs which crawl around for a while before they begin feeding and become immobile. The nymphs are a flat, oval shape, whitish-green in colour, and just over 1mm in length when fully developed. The final nymphal stage is called a pupa and the adult whitefly eventually emerges through a slit in the dorsal surface. The length of the life cycle varies according to the temperature. At 10ºC (50ºF) the life cycle takes several months, but can be completed in about three weeks at 21ºC (70ºF). The pest can remain active during the winter in an unheated greenhouse, provided suitable host plants are present. Glasshouse whitefly does not usually survive winter out of doors.

Image: © GWI/John Swithinbank. Available in high resolution at www.gardenworldimages.com

Advertise here

We love free entry to our local RHS garden

Lucy, mum, part-time lectureer & RHS member

Become a member

Discuss this

for the site or to share your experiences on this topic and seek advice from our community of gardeners.