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How to Kill Thrips Pyrethrum

By Jennifer Loucks ; Updated September 21, 2017

Thrips are a small insect that suck the sap from plants. The insects are black or tan in color and not always visible with the naked eye. Thrips prefer to attack light colored flowers, tomatoes, and some vegetable plants. A plant that is infested with thrips will have foliage that begins to dry and appear white in color due to the insect sucking the out the sap. A thrip has a two-week life span and are present in the garden for five to eight generations.

Gently shake the plant while holding a piece of white paper underneath to see if thrips are present. The bugs are 1/25 inch in size and their dark fecal pellets will fall onto the piece of paper.

Remove leaves infected with thrips and destroy them by placing them in a sealed plastic bag to prevent the bugs from spreading. Do not put thrip infested foliage in a compost bin.

Remove plants that are wilting or completely defoliated from thrips as the plants will not recover. Do not place the plants in a compost bin. Inspect and treat surrounding plants to make sure the thrips have not spread.

Spray the plant with water to knock off any thrips present. Make sure to spray under the leaves to remove thrips from all areas of the plant.

Spray infected plants with three applications of Pyrethrum spray after an infestation has been discovered. Each application should be one week apart. Make sure to spray the plant blossoms and under the leaves to treat all areas.

Keep the plants well watered and mist the plant with water during the hot, dry summer months. Thrips do not like moisture.

Repeat the three application cycle of Pyrethrum spray if the thrips return.


Things You Will Need

  • White paper
  • Flower clipper
  • Water hose
  • Water
  • Pyrethrum spray


  • Pyrethrum spray is available for purchase at garden supply stores.
  • Place a thick layer of organic mulch around plants in spring if there is a known thrip problem. This will prevent the adults from emerging from the ground.

About the Author


Jennifer Loucks has been writing since 1998. She previously worked as a technical writer for a software development company, creating software documentation, help documents and training curriculum. She now writes hobby-based articles on cooking, gardening, sewing and running. Loucks also trains for full marathons, half-marathons and shorter distance running. She holds a Bachelor of Science in animal science and business from University of Wisconsin-River Falls.