Thrips - Okra

Okra

Thrips

Thysanoptera


In a Nutshell

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

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 1-2mm long, yellow, black or both in color. Some varieties have two pairs of wings, while others do not have wings at all. They hibernate in plant residues or in the soil or on alternative host plants. They are also vectors for a broad range of viral diseases. Thrips infest a broad variety of plants. Dry and warm weather conditions favor population growth, while humidity reduces it. Adults can be easily carried by wind, clothes, equipment, and containers not properly cleaned after fieldwork.

Biological Control

Some biological control measures have been developed for specific thrips. The insecticide spinosad 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. Therefore, do not apply spinosad to plants that are flowering. In the case of flower thrips infestation, a combination of garlic extracts with some insecticides also seems to work well. For species that attack the leaves and not the flower, try neem oil or natural pyrethrins, especially on the undersides of the leaves. The use of highly reflective UV mulch (metalized reflective 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, imidacloprid, or acetamiprid, which in many products are combined with piperonyl butoxide to enhance their effect.

Preventive Measures

  • Plant resistant varieties.
  • 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 certified greenhouses and plant nurseries.
  • Monitor fields regularly to assess.
  • Use sticky traps over a large area for mass-catching.
  • Avoid planting near alternative hosts.
  • Prune by cutting plants just above branching points and nodes instead of shearing off terminals.
  • Remove infected plants and any plant debris and destroy them.
  • Keep plants well irrigated, and avoid excessive applications of nitrogen fertilizer.

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