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. For more details see Mosquito Plant, Pelargonium Citrosum – The Citrosa Plant.
What is the Real Citronella Plant
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.
You might also be interested in this post: Mosquito Repellents That Work Against Zika Virus
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. Do they work? I’ve reviewed this in Mosquitoes Repelled By Fragrant Plants.
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.
What Does Work for Mosquitoes?
You will see from the above list that most mosquito repelling devices either don’t work, or work in a very limited way. So how do you keep mosquitoes from biting?
DEET and Picaridin are still your best choice for both safety and efficacy.
Here are some other posts that might interest you.
Mosquito Repellents – Best Options
Mosquito Repelling Devices – Do They Work?
Mosquito Apps for Your Smart Phone – Do They Keep Mosquitoes Away?
Mosquitoes Repelled By Fragrant Plants
Mosquito Repellents That Work Against Zika Virus
References:
1) Efficacy of Citronella Candles and Citronella Incense: http://www.ncbi.nlm.nih.gov/pubmed/8827606
2) Photo Source for Pelargonium Citrosum:
2) Photo Source for Cymbopogon citratus – lemongrass: Public domain from Wikipedia
My garden is full of the little buggers, I gave up trying to stop them biting me & instead now take an antihistamine tablet each morning before I go into the garden, it doesn’t stop them biting, but it stops me reacting to the bites ie no more itching, or swollen lumps from the bites
Does anyone know why *Scent or smell* takes priority in insect deterrent discussions. From what I’ve read here it seems smoke followed by fogging is more successful. Could it be that smoke and fogging make the air *thicker* for an flying insect to pass through or that flying insects can detect *air* differences that humans cannot. Air currents, air quality beyond ordinary human detection. Has science explored this avenue at all?.
I have a friend in my neighborhood that 1 x a week he sprays his entire yard grass bushes and all with a mixture of water, dish soap and vinegar. I kid you not but if you go to any other house in the neighborhood and you get eaten alive by mosquitos but you can lay in the grass in his yard and nothing ! Any thoughts on this or scientific reason for the dish soap mixture? Thanks
I’m just glad I live in North America where the religious cult known as “Peer Review,” often mistaken for “The Science,” frequently mistaken as an authority on actual scientific data and research, has so far chosen not to deny the effectiveness of simple, safe, and traditional chemical free methods of pest control. Maybe it doesn’t work in the EU, or maybe the Peer Review cultists there just don’t like the smell of it. More likely it has to do with them having a particular distaste for all things natural. Who can say with these science fiction artists? All I know is that here in North America we’re able to get along just fine without the chemicals.
Based on your comments you do not understand what “peer review” means. It means a piece of scientific study has been reviewed and checked by other qualified scientists and meets certain minimum standards. It is essentual in the scientific process.
I noticed that over and over it is mention that science disagrees or words to that effect. Science is ever-changing. I remember back in the early 1980s people smoking everywhere and when I would complain I was told that the surgeon general is the time of the second hand smoke does affect us. I remember looking at someone and saying you say that now but one day they’re going to come out and tell the truth. It’s crazy to think you can inhale some of the smoke and it hurts you and all the rest of it comes towards the other people in the office or in the car away over but it doesn’t hurt them. Well guess what? The surgeon general now says secondhand smoke is dangerous to anyone who inhales it.
“Science is ever-changing” – that is not completely true. While science is investigating a subject, it does change frequently. As the process nears the end of investigation, science starts firming up some facts and going forward they are less likely to change. They might change and can change, but normally don’t. For example science has quite certainly decided that the earth is round. Sure, it might change its mind in the future and decide it is square, but that is unlikely.
At any point in time, science has an opinion of a subject. Today science says inhaling cigarette smoke is bad for you. If you come along and say smoke does not harm you, it is quite correct to say science disagrees with you.
I eat alot of garlic and onions and they don’t bother me at all
I don’t want to comment if citronella plants work or not, I would just like to share what bewildered me for quite some time and would like to think that animal instinct has some merit!
I lived right next to the mangroves in North Queensland, and consequentially had a terrible problem with biting midge’s (sand flies) and not so much of a problem with mozzies. To try and combat this problem, I planted 5 cintronella plants along the fence in front of the gate entrance. Over the course of a month I noticed that something was eating the plant closest to the gate, but never noticed any bugs. It was dying and the 2nd nearest started to be affected, then the 3rd when the 1st one died.
One morning after taking the dogs for a walk down the road (off-leash), they stopped off on the way through the gate and ate a couple of leaves off the citronella plant! I was gobsmacked! I had never seen them do this before as they would often go for a wander by themselves or get back home a couple of hunderd metres in front of me.
My dogs would have inevitably also been bitten by the midge’s and I can only assume that they naturally knew that eating the leaves of this plant would help?? How wonderful 🙂
So I wonder if any research has been done on this? Any scientists out there interested?
I love the idea for Citronella plants. I see the Citronella candles at the store and was tempted to buy them. I’m gonna look for the Citronella plants and try those.
Sorry, Robert, but your researchers are wrong. I sit outside in the South every evening. When the mosquitos start biting, I light a citronella candle. Within minutes, the problem is solved. If you think about how a mosquito finds you, it makes sense that the carbon dioxide produced by the candle and the odor of citronella will interfere with the chemoreceptors in their antennae. It isn’t a perfect solution, but citronella candles do indeed work.
So you are saying that your observation, which has no controls, no measurements, and is not published, is more accurate than proper research?
You are missing the whole point of science.
Most people in the south do use citronella candles to repel mosquitoes. If it works why do you need a controlled study? (*you did post that correction that it offered some help in repelling but you preferred deet…which gives me a rash as quickly as I apply it.
You need the study to show it works. Just because people use it does not mean it works.
Okay, so where is your science to back up your claims that it doesn’t work? In fact, the one study you did cite (poorly designed study with no statistical validity) showed a REDUCTION in bites when near a citronella candle.
Yes – a reduction but about the same as the regular candles. This indicates that adding citronella to the candles did not improve their ability to reduce mosquitoes.
So what may I ask sir is your definition of proper research….? Science is based on observations that result in proven factual data…or are inconclusive (whether a controlled or uncontrolled environment) I have personally had positive results with Citronella Plants in repelling mosquitoes. I live in the South. They really come in handy. Seems to me like since your observations (from others experiments) were almost all inconclusive, then you have decided that from your knowledge that Citronella is fairly ineffective. That is called a theory. Just because you published it does not make it more reliable than the next persons Personal Experiences dear.
Proper research follows standards such as using controls, measuring results and applying statistics It is then peer reviewed by other scientists to make sure it follows these rules. And finally it is published in a reputable scientific journal so other scientists can comment on the findings and repeat the experiment.
In this post the citronella plant is not even the correct citronella plant. Its a fake that has a scent to it.
I’d like to offer this to for thought.
we live in south Louisiana and have this plant on the patio.
it doesn’t seem to ward off mosquitos on it’s own but we take the leaves and rub them on our exposed skin. arms, neck, hands, etc.
and we find that it does help to repel them.
for whatever that’s worth.
I can tell you this. the mosquito misters that spray pyrethrins does work. I know many people with them and have experienced it myself.
Thanks a lot Robert for a lot of concised information.