April 2001. A question about tobacco powder as an insecticide. The original message was from Mali and was relayed through Samoa. It concerned a tobacco factory that produced great quantities of tobacco powder as a waste. It seems that market gardeners in that county were using the powder to kill aphids on cabbages. Water is added to the powder which is then sprayed on the plants. The question was whether anyone had experience in using tobacco powder against aphids or other pests.

Members said that although tobacco can be very effective against certain insects, it is, nevertheless, very toxic to mammals and should be used with extreme care.

Sprinkling tobacco powder on recently watered cabbages would create a nicotine solution (of variable, and possibly high concentration) on the leaves, which certainly would kill aphids and other small insects.

Comments were received from a member of the Natural History Museum, UK. Weak nicotine solution (in the form of nicotine soap solution) was used in glasshouses to control aphids and other small insects until the 1970s in the UK. Nicotine is highly toxic, and can be absorbed through human skin with potentially serious or even fatal consequences. A gardener in Kew Gardens was said to have used nicotine soap in the glasshouses, and remembered being sick to his stomach afterwards because he did not know that the use of protective clothing was advisable.

Nicotine is much more toxic to mammals than it is to insects and the use of nicotine solution as an insecticide has been banned in The Natural History Museum as an unacceptable risk to human health.

Since nicotine in solution is able to penetrate human skin, application of dry tobacco powder with dry hands is probably not as hazardous as applying a ready made solution; but the use of gloves, covering the nose and mouth with cloth and the eyes with goggles, and avoidance of prolonged exposure to the powder is still highly advisable.

Caution would also be necessary when harvesting, marketing, preparing and eating cabbages coated with tobacco residue. They would require thorough washing, and the person washing them might be at risk of absorbing nicotine in the process.

It is always worth bearing in mind that the physiology of insects is in many ways not so different to that o human being – so what kills insects often, in sufficient doses, kills or poisons people too.