Pyrethrin insecticide kills insects on contact because it's derived from the pyrethrum daisy (Chrysanthemum cinerariifolium), which contains deadly nerve toxins. This perennial daisy is also nicknamed the Dalmatian chrysanthemum.
Pyrethrin insecticide is commonly produced synthetically by industrial methods, but it also naturally occurs in the pyrethrum daisy flowers. Therefore, it's often considered an organic insecticide. As with all garden chemicals, apply according to the label directions and only when necessary.
In 1840, the active insecticidal attributes of the pyrethrum daisy were first identified in Dalmatia, and commercial production of the flowers ensued.
How to Buy and Use Pyrethrin Insecticide
You can buy pyrethrins in several forms, but the most common are bottled insecticides that contain pyrethrin extract. The dried flower heads are also available, or you can grow your own and dry them. Pyrethrin extract-based insecticides are effective against a wide variety of insects, including soft-bodied insects and chewing and sucking insects such as aphids, leafhoppers, mealybugs, spider mites, stink bugs, scale, thrips, and whiteflies.
Pyrethrin-based insecticides are generally low in toxicity to humans and other mammals, including household pets such as cats and dogs. If you have small children or pets in the house, practice caution when applying any pyrethrin-based insecticides. Pyrethrins are also sold in combination with a number of other products, including copper and sulfur fungicides and piperonyl butoxide.
To use pyrethrin, follow label instructions during the application, wear gloves and protective coverings, and repeat applications as needed to control your insect problem. Depending on the pest target, multiple applications may be necessary. Once the pest problem is under control, stop the applications.
Make Your Own Pyrethrin Insecticide Spray
You can make your own pyrethrin insecticide from homegrown pyrethrum daisies. Once the plant is blooming, pick off the full blooms and dry the flower heads in a cool, dark, and dry place. Store the dried flower heads in a tightly sealed, airtight container. They will retain their effectiveness for up to six months if stored in a freezer. Do not pulverize the flowers until you are ready to mix the insecticide.
When you are ready to use them, wear a protective mask and grind up 1 cup of flower heads to a powder, mix the powder with a little liquid soap to increase the spreadability, and combine with enough water to make a sprayable solution. Pour the solution into a spray bottle. Use the solution as you would a commercial insecticide. The strength of homegrown pyrethrin varies, so feel free to experiment with the proportions until you achieve effective insect control.
Be sure to label the bottle and store it out of reach from any children.
Alternatively, you can use an alcohol extraction process to obtain pyrethrin from the flowers. Soak 1 cup of packed, fresh flower heads in 1/8 cup of 70 percent isopropyl alcohol. Cover the container, and let it sit overnight. The next day, strain the mixture through a cheesecloth and store the homemade extract in a tightly sealed and labeled container. To use, mix the extract with up to 4 quarts of water, and spray on your plants as needed.
Pyrethrin and Garden Safety
Pyrethrin insecticides are biodegradable and will break down within a few days in direct sunlight. The insecticide does not persist in the soil or on the crop, which is why it is relatively safe to use within a vegetable garden.
Remember that pyrethrum is highly toxic to most insects. While it is an effective agent against pests, it can also be deadly to the insects that pollinate your garden and eat pests. It is not wise to spray pyrethrum spray on all your plants. Direct the insecticide only when and where you have a pest outbreak.