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 on outdoor plants such as Viburnum.
Quick facts
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.
Symptoms
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.
Management
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.
Non-pesticide
- 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 thrips. 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
Pesticides
The RHS recommends that you don't use pesticides. Most pesticides (including organic types) reduce biodiversity, including natural enemies, impact soil health and have wider adverse environmental effects.
Where you cannot tolerate thrips, manage them using the information above as your first course of action.
Pesticide treatments are likely to kill natural enemies and so reduce the likelihood of natural control and can lead to resurgence of the target animal.
If you do decide to use 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.
The pesticides listed are legally available in the UK. This information is provided to avoid misuse of legal products and the use of unauthorised and untested products, which potentially has more serious consequences for the environment and wildlife than when products are used legally.
Always follow the instructions on the products. For edible plants, make sure the food plant is listed on the label and follow instructions on maximum number of applications, spray interval and harvest interval.
Homemade products are not recommended as they are unregulated and usually untested.
Be aware that products such as Neem oil are not registered for use in the UK and we cannot advise on their use.
Plants in flower must not be sprayed due to the danger to bees and other pollinating insects.
- If non-pesticide options do not manage the thrips populations, control may be achieved by spraying with pesticides. Spraying at dusk is likely to be more effective
- 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, BugClear Fruit & Veg, Rose Clear 3 in 1 Action, 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 and SB Plant Invigorator). 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. Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer). These products have long lasting action against insects including those that are beneficial
- Pesticides, with both systemic (absorbed and transported through plant tissues) and contact action, are available. These include Flupyradifurone (Provanto Smart Bug Killer) for use on ornamentals and selected edibles and the neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra). These pesticides are widely considered to be the most environmentally damaging, remain active for a long time and will kill beneficial invertebrates
- 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 2, Vitax Greenhouse Smoke Fumigator
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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