Mosquitoes are becoming a more important pest as new varieties move north in North America, and the incidence of diseases increases. Around here there is a big concern about the West Nile Virus so it is only natural that people try to find simple ways to keep mosquitoes away.
A very common solution is citronella. Some suggest planting the citronella plant next to your patio to keep mosquitoes away. Others rely on citronella candles. These solutions are just myths.
What is the Citronella Plant?
As I started researching for this post I was very surprised to learn that the so-called “citronella plant” is not the plant that produces citronella oil – the active ingredient in citronella candles. The picture above shows the citronella plant; also called Pelargonium citrosum. This geranium is unrelated to the true citronella. Not only that but the scientific name of the plant is not even recognized as a valid name. It is a geranium (ie Pelargonium) and it sort of smells like citronella. It even has some of the same aromatic chemicals found in citronella, but it is a different plant.
But does it work? Testing shows that it does not repel mosquitoes. In fact, mosquitoes seem to enjoy sitting on the plant.
Will the Real Citronella Plant Stand Up!
Citronella oil is extracted from various species of lemongrass (genus Cymbopogon – say that name 3 times fast!). This is a perennial clumping grass that grows to a height of 6 feet. It is not frost hardy.
Does Citronella Control Mosquitoes?
So much for botany – does the real citronella plant or the oil work?
Let’s first consider the plant itself. If the aroma from the plant wards off mosquitoes, then this would only work for you if you are sitting in or right next to the plant. The reality is the amount of chemicals given off by plants is very small. You will smell them most when you brush against them or you crush a leaf. Growing the plant will have almost no effect on mosquito control.
Research in North America has confirmed that citronella oil is effective and the oil is registered as an insect repellant in the US. Studies in the EU failed to validate its effectiveness and they have banned the product as an insecticide.We must conclude from this that “we don’t know if it works”, but if Europe can’t find any evidence that citronella oil works, I tend to be skeptical.
If it does work, it does need to be applied frequently – at least every hour.
Citronella oil is a natural product – a good ‘organic product’. Keep in mind that it is also 2 times more deadly than Roundup. Both products are relatively safe, but it is important to understand that this organic solution does have a risk. How toxic is citronella oil? One way to measure toxicity is to measure the LD 50, in this case, the LD 50 on rabbit skin. It turns out citronella oil has a value (4700 mg/Kg) and DEET is (4280 mg/Kg). Both have similar toxicities and both are very safe.
What About Citronella Candles – Do They Keep Mosquitoes Away?
This is a myth. The amount of oil in candles is extremely small and citronella candles don’t work any better than regular candles – neither works well.
Correction: The above statement was the initial entry in the post. It is not quite correct. Work at the University of Guelph tested citronella candles. In a 5 minute period subjects received 6, 8, and 11 bites for citronella candles, regular candles, and no candles, respectively. Citronella candles were marginally better than regular candles and reduced bites by half compared to using nothing. So they work, a bit, but I don’t consider 1 bite a minute as satisfactory. Deet is much more effective.
Fragrant Plants and Mosquitoes
There are lots claims that fragrant plants such as catnip, citronella grass, beebalm, marigolds, lemon balm, lavender, geraniums, thyme, wormwood, rosemary and various mints, repel mosquitoes in the garden.
What Did the Voyageurs Do About Mosquitoes?
The voyageurs were responsible for exploring much of North America for the white man. They traveled through the wilderness with few comforts of home. A million black flies and mosquitoes and no DEET! Just think about that. What did they use? One source, The Voyageurs, suggests that the best repellant was a mixture of bear grease and skunk urine. I guess that after collecting the skunk urine you smelled so bad that even the bugs stayed away. Another source suggests that spruce bows tied around the neck are of some help. I have spent a lot of time in the wilderness and have tried the spruce boughs – I’ll stick to DEET.