Q: I have read about the use of tobacco tea as a biological pesticide.
The Internet has several sites that explain how to make tea with tobacco leaves or with cigarette butts. Once the tea is brewed, add some dish soap and spray on the plants to kill all kinds of insects, including some of the hardest to kill like squash bugs.
I’m a smoker so this seems like a good use for cigarette butts. My question is how safe is this spray for beneficial insects?
A: I would not recommend the use of tobacco tea as a pesticide for three reasons.
First, the nicotine found in tobacco is one of the most toxic substances produced by plants.
According to the National Library of Medicine Archives of Toxicology, nicotine has an LD50 of 6.5 mg/kg, which makes it twice as toxic as arsenic. If tobacco tea were sold as a pesticide, it would have to have a “Danger Poison” label.
Since nicotine can be absorbed through the skin, spilling even a small amount of tobacco tea on your skin could make you sick, depending on the strength of the tea.
The second reason I wouldn’t recommend using tobacco tea is that it is a non-selective pesticide. This means that it kills most insects that come into contact with the spray; even beneficial insects like bees and ladybugs. There are many other insecticides on the market that are more selective and less harmful to beneficial insects.
The third reason not to use tobacco tea in your garden is that tobacco can spread tobacco mosaic virus. TMV can infect a wide range of plant species; tomatoes, peppers and cucumbers are particularly sensitive. Many tobacco products, especially if they contain air-cured tobacco, carry TVM.
The virus is usually spread from plant to plant via “mechanical” wounds caused by the contaminated hands or clothing of tobacco smokers, and by tools used on infected plants such as pruning shears.
TMV is highly infectious because the virus is present in very high concentrations in most plant cells, so only minute amounts of plant material can carry the virus. When plants are handled, the tiny leaf hairs and some outer cells are inevitably damaged and the sap drips onto hands, tools and clothing, allowing the virus to enter the plant. Spraying tobacco tea can also spread the virus to garden plants if the plants have wounds from chewing insects, wind, or human handling.
Symptoms of VMT vary depending on the host plant, age of infected plants, and various environmental conditions. The most common symptoms include plant stunting, mottled leaf spots, leaf curling, and yellowing of leaves and stems.
Once the plant is infected with the virus, there is no cure and infected plants should be immediately removed from the garden and placed in the trash. Do not put them in a compost heap or in green waste, as high temperatures do not kill this virus.
The Shasta Master Gardeners Program can be reached by phone at 530-242-2219 or by email [email protected]. The Gardener’s Office is staffed by volunteers trained by the University of California to answer questions from gardeners using information based on scientific research.