Scale is difficult to kill with poisons. It takes many treatments because you can't coat the entire surface area of the plant, particularly ones that are as densely grown as MD. That suggested to me that we needed to do something more global. My first thought was a hypobaric chamber where we would pump out the air and suffocate the bugs. Tim suggested an anoxic chamber instead where we would remove the oxygen. Friends at work suggested placing a MD in a container and performing the vinegar and baking soda routine within that container. The resulting CO2, being heavier than O2, would displace the oxygen and create a suffocating layer of CO2 for the bugs.
That's a dramatic (and fun!) way to do it, but I think I've got a better one. If we place MD in a big container, add a lit candle to it and then cover it, the candle will consume the O2, replace it with CO and CO2 and similarly suffocate the bugs. Two questions remain: what levels of O2 and CO2 will be deadly to the bugs and how long will it take?
Tim gave us a link to this site that gives us details on how to kill various insects with suffocation.
The results showed that the time required to kill 100% of the insects varied among species and even among the developmental stages of a given species. For most insects tested, exposures of less than 72 hours were required to insure complete kill. Certain stages, such as eggs of cigarette beetles, may require up to 8-day exposures to insure complete kill. Preliminary tests indicated that the addition of CO2 to the nitrogen slightly decreased the exposure time required to kill the insects. However, if increased temperatures or decreased relative humidities could be tolerated by the objects, they would probably have a much greater effect than using CO2 and N2 mixtures in reducing exposure times.That leads us to ask, "At what O2 level will a candle go out?" Here, we found some information from a spelunking site.
When caving in the Arbuckle Mountains, the BIC (lighter) was the air quality instrument of choice though at the time, no one knew how reliable or accurate it was at the time.It sounds to me like the candle will not consume sufficient oxygen to kill the bugs. Still, I think it's worth an experiment since the idea is so easy and inexpensive.
During the course of the state park project, we became curious at what oxygen levels the lighter would start reacting. Using the instruments we set up a number of controlled experiments and verified them with a number of repetitions over several years with different brands.
The lighter will start reacting at 19.5% oxygen. The flame changes color and a small gap will begin to be noticeable between the flame and the jet. At 18% oxygen, the flame will burn about 1 inch above the jet. At 17% oxygen, the lighter goes out and can not be relit. As mentioned earlier, these measurements were very repeatable and could be verified by anyone with the instruments to do so.