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 2mm 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.
Check gladioli 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.
- 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
Pesticide controlThe 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 Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer), fatty acids (e.g. 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 numbers 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 against aphids (e.g. Ecofective Bug Control, RHS Bug and Mildew Control, 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
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.
Pesticides for gardeners (pdf document)
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).
The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.