Gladiolus thrips

Gladiolus thrips can cause a mottling on foliage and flowers of gladiolus.

Gladiolus thrips (Thrips simplex) on gladiolus

Quick facts

Common name: Gladiolus thrips
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. Other species of thrips are unlikely to affect these plants.

Symptoms

White flecks on foliage and flowers of host plants. In heaver attacks, flower petals turn brown and buds fail to open. Rough, grey-brown patches form on the surface of infested corms.

Control

Non-pesticide control

When storing corms from affected plants cut down and dispose of the top growth (either by burning or council green waste) before the corm is fully dried to reduce the number of overwintering thrips, reducing the likelihood of a problem in the following season.

Pesticide control

  • Organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Ecofective Bug Killer), fatty acids (e.g. Solabiol Bug Free, Doff Greenfly & Blackfly Killer) or plant oils (e.g. Vitax Organic 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 aphid numbers in check. Plant oil and fatty acid products are less likely to affect larger predatory invertebrates. 
  • More persistent insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Pest Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer) and cypermethrin (e.g. Py Bug Killer)
  • 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

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

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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