Tobacco contains nicotine, which is a very toxic organic poison. Leaves and stems of the tobacco plant are used to prepare extracts which can be applied to control certain insects (aphids, caterpillars, thrips, leaf miners) and mites.
As an example, here is one method of producing a tobacco extract:
Mix 250 gram of tobacco (for example obtained by collecting cigarette subs) with 4 liters of water. Add 30 gram soap. Boil this mixture softly for 30 minutes, then filter it. Add 16 liters of water and mix it well. Use a sprayer with a nozzle producing a small droplet size.
The best results with tobacco extracts are obtained at temperatures above 30 ºC.
Sometimes tobacco powder can be used against certain insects such as thrips. It can be prepared by grinding dried leaves and stems.
But some warning are needed:
Nicotine is very toxic to mammals, both via ingestion and via contact with the skin. Therefore, contact with the extracts should be avoided during preparation and spraying. Maintain a waiting period of at least 4 days, before harvesting products that were sprayed with tobacco extracts.
Just like most synthetic insecticides, nicotine will also kill beneficial insects. Its use should therefore be avoided as much as possible.