Pyrethrin, the flower power of pesticides, comes from chrysanthemum flowers. It is one of the best all around pesticides out there. It kills such a wide spectrum of pests and is relatively safe for humans and pets when used as per the label. While pyrethrins have been widely used (even back in the 1800s), recently the pest control industry has moved to synthetic versions. This is because 70% of the chrysanthemum crop is grown in Kenya which has been very unstable politically. Another reason the synthetic version is popular is because it has a longer residual time, meaning the chemical lasts longer once it has been applied.
Do Not Mix Chemical Too Strong
Sunlight and heat are two of the biggest enemies of pyrethrins. A treatment in direct sunlight in 100 degree heat will not last as if it were applied in the shade at 60 degrees. Do not worry; if you apply these products as the label recommends, you should be fine. One of the most common mistakes a do-it-yourselfer makes is mix the product too strong. The manufacturers have spent, in many cases, thousands of dollars to make these products. They have spent countless hours testing them. Trust them; they know what they are doing.
They would sell a lot more product if they gave a higher mix rate. Tests prove that many times when these products are mixed too strong, it can repel the pest. The pests will actually notice the chemical before they get a lethal dose. Read and understand the label. The label is the law. Pyrethrins are a neurotoxin. It attacks the central nervous system, which affects the muscle receptors and keeps them from firing properly. While this sounds scary, the EPA has stated pyrethrins are one of the safest products to be used on food producing plants, when used as the label prescribes.
Read the Label!
You must be very careful with pyrethrins when using around fish or tadpoles as they are extremely sensitive to this chemical. Do not spray near ponds and do not apply when it is raining. Rain water run-off could carry the product directly to a creek or your pond. Once again, remember the label will tell you about all these precautions. Make sure you read and understand the label before you purchase, mix, apply, or store any pesticide.