Thrips

  • Symptoms

  • Trigger

  • Biological Control

  • Chemical Control

  • Preventive Measures

Thrips

Thysanoptera

Insect


In a Nutshell

  • Small silver patches on upper leafside.
  • Yellowing of leaves.
  • Deformation of leaves, flowers and fruits.

Hosts:

Apple

Pear

Grape

Raspberry

Bean

Eggplant

Cherry

Apricot

Plum

Peach

Carrots

Pea

Cucumber

Pumpkin

Zucchini

Tomato

Cabbage

Lettuce

Potato

Black & Green Gram

Pigeonpea & Red Gram

Chickpea & Gram

Cotton

Wheat

Soybean

Other

Onion

Garlic

Rice

Sorghum

Maize

Strawberry

Currant

Olive

Banana

Sweet Potato

Peanut

Mango

Papaya

Manioc

Rose

Pomegranate

Ornamental

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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. Thrips do infest a broad variety of plants. Dry and warm weather conditions favor population growth. Humidity reduces it. Adults can be easily carried by winds, clothes, equipment and containers not properly cleaned after field work.

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 fipronil @2 ml, imidacloprid @ 0.25 ml or acetamiprid @ 0.2 g, which in many products are combined with piperonyl butoxide to enhance their effect.

Preventive Measures

  • Plant resistant varieties that do not require insecticide applications for thrips.
  • Add plastic or organic mulch along the rows to reduce the incidence and progression of thrips.
  • Avoid planting susceptible plants next to the weedy areas.
  • Use virus- and thrips-free transplants from greenhouses that manage thrips and inspect transplants.
  • Monitor fields regularly to assess the incidence of a disease or pest and determine their severity in order to plan the appropriate measures.
  • Use sticky traps over a large area for mass-catching.
  • Avoid planting near alternative hosts or plants infected with viruses.
  • Prune by cutting plants just above branching pointsand nodes instead of shearing off terminals.
  • Greenhouses could be sterilized with steam between plantings.
  • Remove infected plant and any plant debris and destroy it.
  • Keep plants well irrigated, and avoid excessive applications of nitrogen fertilizer.