Thrips

  • Symptoms

  • Trigger

  • Biological Control

  • Chemical Control

  • Preventive Measures

Thrips

Order Thysanoptera

Insect


In a Nutshell

  • Small silver patches appear on the upper side of leaf blades, an effect known as "silvering".
  • Yellow, black or fasciated, insects of 1-2 mm in length and black dung spots on underside of the leaves.
  • Deformation of leaves, flowers and fruits.

Hosts

Additional

Apple

Apricot

Bean

Cabbage

Capsicum & Chili

Carrots

Cherry

Cotton

Cucumber

Currant

Eggplant

Garlic

Lettuce

Maize

Mung bean

Olive

Onion

Ornamental

Pea

Peach

Peanut

Pear

Potato

Pumpkin

Raspberry

Red gram, Pigeonpea

Strawberry

Sweet potato

Tomato

Zucchini

Symptoms

Larvae and adults feed on plant tissues and produce small silver patches on the upper side of leaf blades, an effect known as 'silvering'. The same patches can appear on petals where the pigment has been removed. On the underside of the leaves, the thrips and their larvae sit together in groups alongside their black dung spots. Leaves of affected plants yellow, wither, deform or shrivel. Feeding during bud or flower development later results in scarred, stunted or deformed flowers or fruits respectively and loss of yield.

Trigger

Thrips are 1-2 mm long, yellow, black or fasciated insects. Some varieties have two pairs of wings, others do not have wings at all.They hibernate in plant residues or in the soil or on alternative hosts plants. They are also vectors for a broad range of viral diseases. Dry and warm weather conditions favor population growth. Humidity reduces it.

Biological Control

Some biological control measures have been developed for specific thrips. Predatory mites that feed on larvae or pupae are commercially available. Against varieties that attack the leaves and not the flower, try neem oil or natural pyrethrins, especially on the undersides of the leaves. Spinosad application is generally more effective against thrips than any of the chemical or other biological formulations. It lasts 1 week or more and moves short distances into sprayed tissue. It can however be toxic to certain natural enemies (e.g., predatory mites, syrphid fly larvae) and bees. Do not apply spinosad to plants that are flowering. In case of flower thrips infestation, some predatory mites or green lacewing larvae could be used. A combination of garlic extracts with some insecticides also seem to work well. Use of highly reflective UV mulch (metalized mulch) has been recommended.

Chemical Control

Always consider an integrated approach with preventive measures together with biological treatments if available. Due to the high reproductive rates and their life cycles, thrips have developed resistance to different classes of pesticides. Effective contact insecticides include azadirachtin, fipronil and pyrethroids, which in many products are combined with piperonyl butoxide to enhance their effect.

Preventive Measures

Plant resistant varieties of the crop of choice.,Resistant varieties generally do not require insecticide applications for thrips.,Use virus- and thrips-free transplants from greenhouses that manage thrips and inspect transplants.,Use sticky traps over a large area for mass-catching.,Avoid planting near alternative hosts or plants infected with viruses.,Greenhouses could be sterilized with steam between plantings.,Monitor for thrips and control weeds in and around the field.,Remove infected plant and any plant debris and destroy it.,Keep plants well irrigated, and avoid excessive applications of nitrogen fertilizer.