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 on outdoor plants such as Viburnum.
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?
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.
Since 2010 glasshouse thrips has become common out of doors on evergreen shrubs in parts of southern England, viburnums and some other evergreen shrubs are often affected.
Check susceptible plants frequently from spring onwards so action can be taken before a damaging population has developed. WWhen choosing management options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section and avoiding pesticides. Within pesticides the shorter persistence products (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. Pesticide treatments are likely to kill natural enemies and are only likely to be successful if the entire plant can be reached.
- 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 a predatory bug (Orius laevigatus) and 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’. The nematodes can potentially affect other insects and the predators can feed on invertebrates other than sciarid fly larvae. These can be purchased from biological control suppliers (downloads pdf document)
- Encourage natural enemies in gardens, for example the predatory bug Orius laevigatus can occur naturally
- 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
- The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.
- Organic sprays, such as natural pyrethrum (e.g. Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear Fruit & Veg, Vitax Rose Guard) can give good control of thrips. These pesticides have a very short persistence and so may require reapplication to keep thrips numbers in check. THrips hidden in distorted leaves may be unaffected by these products. Plant oil and fatty acid products are less likely to affect larger insects
- Plant invigorators combine nutrients to stimulate plant growth with surfactants or fatty acids that have a physical mode of action against thrips (e.g. Ecofective Bug Control, Growing Success Bug Stop, Rose Clear 3 in 1 Action SB Plant Invigorator and Westland Resolva Natural Power Bug & Mildew). These products contain some synthetic ingredients and so 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)
- A systemic containing the active ingredient Flupyradifurone (Provanto Smart Bug Killer) is available for use on ornamentals and selected edibles
- The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
- 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
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.
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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