Glasshouse thrips

Glasshouse thrips cause a fine silvery mottling of the upper leaf surfaces on many glasshouse plants and some plants outdoors. In some areas glasshouse thrips have become a frequent problem on outdoor plants such as Viburnum.

Glasshouse thrips damage on viburnum

Quick facts

Common name Glasshouse thrips
Scientific name Heliothrips haemorrhoidalis
Plants affected Many glasshouse vegetables and ornamental plants. Outdoor plants, particularly Viburnum tinus hedges can also be affected
Main symptoms Silvery mottling and brown marks
Most active April to September but all year round in glasshouses

What are glasshouse thrips?

Thrips (also known as thunder flies) are small insects, many of which feed by sucking sap from leaves and flowers. Glasshouse thrips adults have narrow dark brown bodies up to 2mm in length with an orange tipped abdomen. They have pale yellow antennae, legs and wings which are fringed with short hairs and folded back over the abdomen whilst at rest. Several other species of thrips may be encountered in gardens. 

Symptoms

The feeding activities of glasshouse thrips cause a fine pale mottling of the upper leaf surfaces and affected foliage usually develops a silvery colouration. The foliage is also marked with small red-brown spots caused by the thrips excrement. When feeding occurs on developing shoot tips or flower buds it is likely to cause distorted growth.

Control

Check susceptible plants frequently from spring onwards so action can be taken before a damaging population has developed. When choosing control options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section. If this is not sufficient to reduce the damage to acceptable levels then you may choose to use pesticides. Within this group the shorter persistence pesticides (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action.

Non-pesticide control

  • Tolerate some thrips damage, despite extensive silvery mottling established outdoor shrubs will usually survive the presence of this insect 
  • Biological controls are available for use in glasshouses. These include predatory mites, Amblyseius species, Hypoaspis species and Macrocheles roibustulus (sold as Mighty Mite). There is also a nematode biological control sold as Fruit and Vegetable Protection’.  These can be purchased from biological control suppliers (downloads pdf document)   
  • Hanging blue sticky traps (widely available from garden suppliers) above or among the plants in glasshouses can trap thrips and help monitor and reduce numbers. This is not recommended out of doors as the traps will capture a large number of non-target invertebrates

Pesticide control

  • Organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer), fatty acids (e.g. Solabiol Bug Free, Doff Greenfly & Blackfly Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear for Fruit and Veg) can give good control of thrips. These pesticides have a very short persistence and so may require reapplication to keep thrips in check. Plant oil and fatty acid products are less likely to affect larger insects such as ladybird adults. 
  • Plant invigorators combine nutrients to stimulate plant growth with surfactants or fatty acids that have a physical mode of action (e.g. Ecofective Bug Control, RHS Bug and Mildew Control, SB Plant Invigorator and Westland Resolva Natural Power Bug & Mildew). These are not considered organic
  • More persistent contact-action insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer)
  • In glasshouses it is possible to use glasshouse fumigants. Glasshouse should be sealed and instructions on the product label must be followed. An organic fumigant based on garlic is available as Pelsis Pest-Stop Biofume Greenhouse Fumigator and can be used when crop plants are present. Products based on the synthetic pyrethroid permethrin are available as DeadFast Greenhouse Smoke Generator, DeadFast Greenhouse Smoke Fumigator
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
Follow label instructions when using pesticides. On edible plants make sure the food plant is listed on the label and follow instructions on maximum number applications, spray interval and harvest interval.
Plants in flower should not be sprayed due to the danger to bees and other pollinating insects.
Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener.

Downloads

Pesticides for gardeners (pdf document)
Biological control suppliers (pdf document)
 

Biology

Adults glasshouse thrips can lay up to 100 eggs at a rate of one or two per day. These are often deposited on the younger leaves or in flower buds of host plants.

The immature stages (nymphs), are yellow-brown and have three stages of development. The first two stages, like the adults, feed by sucking sap and are entirely wingless. ‘Wing buds’ develop on the third stage which does not feed and is known as a pre-pupal stage. The pre-pupal and pupal stages take place in the soil and in sheltered places on the host plant. Wings are not fully formed until the adult thrips emerge. 

The length of the life cycle varies and is affected by temperature. Under warm conditions the life cycle is completed in 24-35 days and glasshouse thrips can breed throughout the year.

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