23 Jan Thrips

Description: Thrips are the secret agents of the plant pest world. They are small at generally only 1-2mm long and lurk in sheltered positions either deep in flower buds or the undersides of leaves where they go undetected. Thrips come in various colours from yellow, white and brown and black. Generally it is their damage that is noticed first rather than the pest.

Damage Caused: Thrips have what is called a rasping and sucking mouth which they use to damage the leaf surface and suck up the sap that subsequently flows (unlike piercing insects that inject a mosquito-like mouthpart into the leaf to draw on the sap). This gives leaves a silver-brown mottled appearance on the upper side of leaves. Some thrips inhabit the inside of flower buds where they prematurely age the bloom with this same rasping and sucking action causing them to brown-off. If in sufficient numbers they will weaken the plant considerably. Thrips can also be credited with the spread of plant viruses.


Green: Horticultural soaps (eg. Natrasoap) and oils (eg. Eco-Oil) sprays are useful for both vegetable and ornamental gardeners. Soap sprays work by dissolving the exoskeleton of the pest killing it. Oils sprays work by smothering the pests, blocking their breathing (which they do through their body) and killing them. Application to the entire plant (including undersides of leaves is crucial when using these types of products, as they require you to get the spray onto each pest present for successful control.

NB Do not apply oil sprays in temperatures exceeding 25C as this will likely burn foliage.

Blue sticky traps work well in limiting pest numbers and as an identification tool to let you know when to start spraying with botanical oils, horticultural soaps, etc.

Orange: Only ornamentals should be treated with systemic insecticides (eg. Confidor, Maxguard), which penetrate into the plants sap system that the pests feed on. They are highly efficient at killing these pests and last on average two weeks in the plants system. As they are systemic the spray does not have to make contact with the pest itself to work and insects can be killed in areas of the plant not reached by the spray (though thorough application is recommended) . These sprays are invaluable for treating pests in situations such as hedging where contact with individual pests is not always possible.

NB Care should be taken when spraying these above chemicals is they harm foraging bees. As a rule I only use these on plants that are not currently in flower to avoid the risk to bees that are so vital in the garden.

Red: Not required for this pest.




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  • Steve
    Posted at 20:44h, 23 January Reply

    The best thrip control I know is eco-neem.  It’s not on the label as it hasn’t been registered for that yet in Australia (overseas it is) but it still does a great job.  Plus it’s Certified Organic and doesn’t harm bees or other good bugs.

    • Hortiman
      Posted at 00:40h, 25 January Reply

      Great to hear eco-neem works so well Steve! I will have to give it a try should my Viburnums be attacked this season 🙂

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