Pyrethrum

Pyrethrum was a genus of several Old World plants now classified as "Chrysanthemum" or "Tanacetum" (e.g., "C. coccineum") which are cultivated as ornamentals for their showy flower heads. Pyrethrum continues to be used as a common name for plants formerly included in the genus "Pyrethrum". Pyrethrum is also the name of a natural insecticide made from the dried flower heads of Chrysanthemum cinerariifolium and Chrysanthemum coccineum. Its active ingredient are pyrethrins.
Description.
Some members of the genus "Chrysanthemum", such as the following two, are placed in the genus "Tanacetum" instead by some botanists. Both genera are members of the daisy (or aster) family, Asteraceae. They are all perennial plants with a daisy-like appearance and white petals.
Insecticides.
Sprays.
Pyrethrum has been used for centuries as an insecticide, and as a lice remedy in the Middle East (Persian powder, also known as "Persian pellitory"). It was sold worldwide under the brand Zacherlin by Austrian industrialist J. Zacherl. It is one of the most commonly used non-synthetic insecticides allowed in certified organic agriculture.
The flowers should be dried and then crushed and mixed with water.
Toxicity.
Rat and rabbit levels for pyrethrum are high, with doses in some cases of about 1% of the animal's body weight required to cause significant mortality. This is similar to fatal levels in synthetic pyrethroids. Nevertheless, pyrethrum should be handled with the same caution as synthetic insecticides.
People can be exposed to pyrethrum as a mixture of cinerin, jasmolin, and pyrethrin in the workplace by breathing it in, getting it in the eyes or on the skin, or swallowing it. The Occupational Safety and Health Administration (OSHA) has set the legal limit (Permissible exposure limit) for pyrethrum exposure in the workplace as 5 mg/m3 over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a Recommended exposure limit (REL) of 5 mg/m3 over an 8-hour workday. At levels of 5000 mg/m3, pyrethrum is immediately dangerous to life and health. People exposed to pyrethrum may experience symptoms including pruritus (itching), dermatitis, papules, erythema (red skin), rhinorrhea (runny nose), sneezing, and asthma.
People using pyrethrum should wear safety equipment. It is a chemical that should be kept apart from other chemicals.
Companion planting.
Because pyrethrum contains pyrethrins and aphid alarm pheromone, they are used as companion plants to repel pest insects from nearby crops and ornamental plants. They are thought to repel aphids, bed bugs ("Cimex lectularius"), leafhoppers, spider mites, harlequin cabbage bugs, ticks, pickleworms, and imported cabbage worms, among others, in gardens and farms. For example, they are planted among broccoli plants for protection from several common insect pests. The alarm pheromone both attracts ladybug beetles and repels aphids 
Common names.
Common names for "Chrysanthemum cinerariifolium" include:
Common names for "Chrysanthemum coccineum" include: