Gladiolus thrips
Gladiolus thrips can cause a mottling on foliage and flowers of gladiolus.
Quick facts
Scientific name: Thrips simplex
Plants affected: Primarily gladiolus
Main symptom: White flecks on foliage and flowers
Most active: July-September
What are gladiolus thrips?
Gladiolus thrips are small, narrow 2 mm long, brownish-black insects that suck sap from gladiolus and some other plants including crocus, freesia, iris and lilies. There are several other species of thrips that gardeners may find casuing damge to plants, none of these affect gladioli.
Symptoms
Management
Check gladioli frequently from spring onwards so action can be taken before a damaging population has developed. When 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 the presence of some thrips damage
- Encourage natural enemies in gardens, for example the predatory bug Orius laevigatus can occur naturally
- When storing corms from affected plants cut down and dispose of the top growth (preferably in council green waste) before the corm is fully dried to decrease the number of overwintering thrips, reducing the likelihood of a problem in the following season
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
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.
Download
Pesticides for gardeners (pdf document)
Biological control suppliers (pdf document)
Biology
Adult gladiolus thrips are 2mm in length, brownish-black and have narrow, elongate bodies. Adults 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 pale yellow. There are three nymphal stages (instars).
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.
Gladiolus thrips usually has two or three generations a year but may have more during hot summers. The thrips overwinter concealed on stored corms and can even continue to reproduce as long as the temperature remains above 10°C (50°F).
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