Chrysanthemums contain insecticidal subtances, but some varieties work better than others.
Diseases spread by mosquitoes have killed more people than all the wars in history, according to the Illinois Dept. of Public Health. Encephalitis, meningitis, West Nile virus and malaria are just some of the diseases these pests transmit. Finding an effective mosquito repellent is important, but many people don't like to use chemicals like DEET because of possible health risks. Botanical insecticides are perceived as being safer because they're "natural." According to plant pathologist Laura Pickett Pottorff, pyrethrums are the most commonly used botanical insecticide in the United States. Their active ingredient, pyrethrin, comes from chrysanthemums. Does this Spark an idea?
Pyrethrums
Pyrethrums are found in Dalmatian chrysanthemums (Chrysanthemum cinerariaefolium) and Persian chrysanthemums (Chrysanthemum coccineum), although there are less of them in the Persian variety. Insecticidal substances can also be found in other types of chrysanthemums, including C. balsamita and C. marshalli, but they don't work as well as the pyrethrum chrysanthemums. Commercial production of pyrethrums occurs in the mountainous areas of Africa and South America, but the plants can also be grown in North America. According to agriculturist Jean Duval, the level of pyrethrins in North American plants may not be as high as those grown near the equator.
Home Remedies
Hang chrysanthemums upside down in water for 24 to 48 hours prior to drying to increase levels of pyrethrin. Burn the uncrushed flowers to repel mosquitoes. An insecticidal spray to kill insects on plants can be made by soaking 7/10 oz. of dried and crushed flowers in 1 1/2 gallons of warm water for three hours. Adding a teaspoon of canola oil, sesame oil or nutmeg oil will increase effectiveness. Flowers crushed into a fine powder are more effective than those coarsely crushed, but the pyrethrum in them will also break down faster. Pyrethrins decompose in a few days time when exposed to light or heat. Keep crushed flowers in the freezer for up to six months to preserve potency.
Pesticides
The pyrethrins found in chrysanthemums work by infiltrating the nervous system of mosquitoes and other insects and paralyzing them, thus knocking them to the ground. They don't kill mosquitoes, however, because insects can detoxify natural pyrethrins with enzymes they produce. In order to be an effective pesticide, other ingredients have to be added to the pyrethrins to enhance their effect. These other ingredients are known as synergists.
Toxicity
Although the pyrethrums found in chrysanthemums are considered to be one of the safest insecticides in use, the Environmental Protection Agency (EPA) does require that a "Caution" notice be placed on products containing them. That's because high levels of pyrethrins can cause symptoms like dizziness, headache, nausea, muscle twitching and even convulsions. The amount of pyrethrin residues permitted in various foods ranges from .01 to 75 parts per million (ppm) and is regulated by the EPA. The Occupational Safety and Health Administration (OSHA) doesn't allow more than 8 milligrams of pyrethrins per cubic meter of workplace air during an eight-hour shift. Pyrethrins are also very poisonous to fish and other aquatic life and slightly poisonous to birds.
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