For years, agriculturalists have used carbon dioxide to kill insects in sealed vegetable, grain and fruit storage containers. The benefits are obvious: Because CO2 is not a chemical insecticide, it does not leach into the food, making it totally safe for human consumption.
But does that mean CO2 can be used to fumigate live plants? While the evidence says “yes”, it isn’t an easy solution.
The first problem with using CO2 to fumigate is that to be effective, the CO2 level must be maintained above 40% over 7-15 days in order to kill every type of insect. For example, in their paper Carbon dioxide as a potential fumigant for termite control, researchers at the University of Hawaii found that exposure to 50% carbon dioxide for 60 hours resulted in approximately 70% termite mortality, while complete mortality was recorded after 120 hours.
Not only must CO2 levels be kept high long enough to kill all the adults, it must also be kept high long enough to kill the offspring that hatch several days later.
Another problem is that in order to create a high CO2 environment over several days, extreme caution must be taken. CO2 levels above 4% will cause headaches and loss of balance, while levels above 8% will result in loss of consciousness in a few minutes.
Lack of knowledge of proper handling of CO2 can be deadly. For example, the Food & Fertilizer Technology Center for the Asian and Pacific Region originally showed on their website workers using cloth masks while filling a grain storage facility with toxic levels of CO2. Although the workers are not aware of it, these masks are useless. Whenever attempting to create a closed environment with high levels of CO2, a self-contained breathing apparatus should be used.
The other factor is that while CO2 fumigation is generally safe for stored produce, at high levels it can stunt plants. This is usually accompanied by chlorosis or necrosis of the foliage.
Even with all these issues, high levels of CO2 is an effective fumigation technique. Scientists at UC-Davis describe the CO2 levels and times required to kill various insects. Clearly, some pests are much less tolerant of high levels of CO2 than others. In addition, indoor growers have reported in blogs and online user groups that high concentrations for short periods of time several days apart can achieve the same killing effect.
Although high levels of CO2 is effective for fumigating stored produce and grains, it should be used carefully as a solution for fumigating live plants. CO2 at high levels is toxic to humans, and should only be used with the proper monitoring tools.