Pyrethrum spray is an insecticide derived from the dried flowers of specific chrysanthemum species, particularly Chrysanthemum cinerariifolium, often called the pyrethrum daisy. Compounds extracted from these flowers are used in pest control to manage various insect populations.
This spray controls insect pests in environments like gardens and homes. It works by affecting insects, leading to their paralysis and eventual death. Its natural origin makes it a consideration for those seeking naturally derived pest control options.
What Pyrethrum Spray Is and How It Works
Pyrethrum spray is derived from the dried flowers of Chrysanthemum cinerariifolium, a plant native to northeastern Europe, Asia, and Eastern Africa. These flowers contain six naturally occurring insecticidal compounds known as “pyrethrins,” including pyrethrin 1, pyrethrin 2, cinerin 1, cinerin 2, jasmolin 1, and jasmolin 2.
Pyrethrins target the nervous systems of insects. They are nerve toxins that act on voltage-gated sodium channels in the insect’s nerve cell membranes. Normally, these channels open and close to allow sodium ions to pass through, which helps nerve cells communicate and generate responses like movement.
Pyrethrins prevent these sodium channels from closing properly, causing the nerve cells to remain depolarized. This sustained depolarization leads to continuous nerve firing, resulting in paralysis and rapid knockdown of the insect. This ultimately leads to its death.
It is important to distinguish natural pyrethrins from “pyrethroids.” Pyrethroids are synthetic compounds designed to mimic the insecticidal effects of natural pyrethrins. While they share a similar mode of action, pyrethroids are often modified to be more stable and persistent in the environment compared to natural pyrethrins, which break down quickly when exposed to sunlight and air.
Key Uses of Pyrethrum Spray
Pyrethrum spray is effective against a broad range of insect pests due to its rapid action. It controls soft-bodied chewing and sucking insects. Pests include aphids, mosquitoes, fleas, ants, flies, whiteflies, leafhoppers, thrips, caterpillars, mealybugs, beetles, and spider mites.
This insecticide is used in various settings. In gardens, it controls pests on fruits, vegetables, and ornamental plants. Within homes, it targets pests like ants, cockroaches, and flies.
Pyrethrum is also found in some personal care products. For example, it is an active ingredient in certain treatments for head lice, crab lice, and their nits in humans.
Important Considerations for Use
Despite its natural origin, pyrethrum is a broad-spectrum insecticide, meaning it does not selectively target only pest insects. It can harm beneficial insects such as bees, ladybugs, and other pollinators and predators. Bees, for instance, are highly sensitive to pyrethrins, with even microgram doses capable of being lethal through ingestion or direct contact.
Pyrethrum also poses a significant risk to aquatic life. It is highly toxic to fish and aquatic invertebrates like lobsters, shrimp, mayfly nymphs, and zooplankton. Concentrations as low as less than 1.0 parts per billion can be lethal to fish such as bluegill and lake trout. Preventing runoff into ponds, streams, and other water bodies is therefore important to protect these sensitive ecosystems.
Pyrethrum breaks down rapidly in the environment. It is unstable when exposed to light and air, with a half-life often less than 24 hours. This rapid degradation reduces its environmental persistence compared to many synthetic alternatives.
While generally considered to have low toxicity to humans and pets in diluted forms, proper handling remains important. Direct contact with concentrated forms can cause irritation to the skin, eyes, or respiratory system, potentially leading to symptoms like burning, runny nose, coughing, or difficulty breathing. Individuals with asthma or allergies to chrysanthemums, marigolds, or daisies may experience allergic reactions.
Safe and Effective Application
Always read and follow the specific instructions on the product label. These labels provide detailed guidance on mixing ratios, application rates, and target pests, which are designed to ensure both effectiveness and safety. Adhering to these guidelines is essential for proper use.
Apply pyrethrum spray during calm weather conditions to prevent drift to non-target areas or organisms. Apply in the late evening, at night, or early morning. This timing minimizes exposure to beneficial insects like bees, which are typically less active during these hours.
To protect beneficial insects, avoid spraying directly onto flowers where pollinators may forage. Avoid direct contact with skin and wear protective gear, such as gloves and safety glasses, if recommended by the product label. Ensure adequate ventilation if applying indoors.
Preventing runoff into water sources is important due to pyrethrum’s toxicity to aquatic life. Do not spray plants to the point of runoff or dripping, and avoid application near ponds, lakes, or streams. Store the product in a cool, dry, well-ventilated place, away from foodstuffs and direct sunlight, with containers kept closed.