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Whilst bonsai trees are a fantastic hobby to get to grips with, one of the problems associated with the art of bonsai that I had to deal with is an increase in the number of pests when compared to other horticulture activities. It’s not uncommon then for flies and scale to be common, however, something slightly more worrying is white powder on bonsai leaves, so what exactly is this?
White powder, white film, or white powdery mildew on bonsai leaves is a surefire sign that your bonsai has a fungal infection. This is particularly common in broadleaf species like Chinese Elm. To remove, simply wipe down and use fungicide regularly.
So how exactly can you treat your bonsai for white powder mold and fungal infections? And can this powder be dangerous to your plant? Keep reading to find out more.
A lot of you reading this post are just getting started with bonsai. You can find my recommendation for the best bonsai I found here (link takes you to Easternleaf) or the best faux bonsai here (link takes you to Amazon)
White powder on bonsai leaves
Whilst a lot of us knew that getting into bonsai would mean a lot of patience and care the truth is that keeping bonsai will meet at some point, sooner or later we will need to deal with infestations.
Whilst I’ve already covered how to deal with scale infestations – (check out this post if you are currently struggling with brown spots on your bonsai,) like children, bonsai trees are also susceptible to more than one infestation and that leads us to a major problem that is all too common.
So what exactly is this white powder, well to help summerise I’ve summarised the main points below:
- A white powder-like substance on a bonsai is most commonly associated with a mold or fungal infection on your plant.
- Whilst this most commonly resembles a white powder it can also look like a thin white film on your tree.
- Most minor infestations of fungus or mold can be treated fairly easily with things like plant fungicide – think of them as an athletes foot spray for your plant
- Another homemade option to treat would be to use something like rubbing alcohol, and soapy water to neutralize the white powder.
- More extreme cases of white powder may need to be taken to a specialist.
What causes white powder on bonsai trees?
Sadly, because bonsai trees are made up of so many different species, it can be very easy for them to suffer from regular fungal and mold infections.
White powder on your bonsai trees is caused by 2 main factors
- In some situations mold
White powder caused by fungus
White powdery mildew is the most common type of white powder that will affect your bonsai. It is caused by a fungus that thrives in dry soil conditions both damp or dry climates.
This white fungus then will typically start on the top of your bonsai leaves and if left unchecked will typically start to spread to the underside of your bonsai and then to the stems of your plant.
If left unchecked your bonsai leaves will start to turn yellow before turning brown, drying up, and falling off – something we don’t want with bonsai trees!
This white powder, caused by a fungus, can be common in any plant but will especially take hold of younger bonsai or bonsai that are unhealthy – meaning bonsai that you keep indoors will likely be a lot more susceptible.
How to treat white powder on bonsai caused by fungus?
So it’s more likely than not that your bonsai’s white powder is caused by a fungus so we must treat it as soon as we notice it.
The best option to treat white powder on your bonsai caused by fungus is to use a plant fungicide.
I personally like to use Bioadvanced fungicide (link will take you to Amazon) as not only will it do a fantastic job in getting rid of any fungus, it also acts as an insecticide, helping remove any pesky insects that may be damaging your plant.
To treat white powder effectively it would be best to follow these steps:
- Remove your bonsai from any surrounding plants to ensure the fungus does not spread
- Put on a pair of gloves to avoid getting the antifungal spray on your skin
- Wipe down your bonsai as best you can to remove the top layer of any white powder on your bonsai
- Spray your plant leaves with a fungicide spray, aiming directly for the leaves to ensure a nice even distribution around the leaves.
- Leave your plant for 24 hours then repeat this process once more.
A few sessions of doing this, typically over two weeks, should ensure that your white powder will disappear.
It’s important however that you play this by ear as the fungus will work differently depending on the size and health of your bonsai as well as the plant breed you are working with.
How to treat more serious causes of white powder/mildew on your bonsai?
Now whilst using the fungicide should work for most of you, if your bonsai is too far gone to the point where your leaves are already discolored and the plant looks like a sad excuse of a bonsai you will need to see a specialist.
Most garden centers have bonsai clinics to address just these problems and will be professionally set up to deal with fungal outbreaks (seriously it’s literally their day job)
So if you have tried fixing the problem yourself to no avail, get in touch with your local garden center.
How to ensure you don’t get white powder on your bonsai?
Once we have successfully treated the white powder on your bonsai, the next step we need to follow is all-around prevention.
To prevent your bonsai from getting this white powder again, come up with a routine, where you spray your bonsai with fungicide at least once per week. It’s also important to regularly check for further white powder outbreaks so spend a few minutes every week inspecting your bonsai.
White powder on bonsais is typically caused by dry topsoil or insufficient soil conditions.
If you feel as though your bonsai has poor soil quality consider replanting your soil or keeping your soil moist to avoid white powder caused by dry soil.
Regular watering then is essential, so aim to water your bonsai at least once per day and consider also investing in a moisture tray.
Moisture trays in particular can be fantastic options especially if you live in a dry climate – to read up more about this check out my post here.
Another brilliant option to avoid white powder is just to maintain a regular temperature year-round.
Sadly white powder mildew is incredibly resilient growing both in warm and cold climates however, a trick I learned that works is to try and keep a contact temperature to help ket your bonsai adjust.
Greenhouses typically work best for this.
“Most white powder on bonsai trees is cuased by fungal infections”
White powder caused by mold
White powder caused by mold is less common, as this usually causes things like rust infections or other discolorations. That being said in some situations that can also cause white powder.
Two main types of mold can attack your bonsai:
Pathogenic mold is usually caused by a poor soil mix.
What typically happens in this scenario, is that leaves and other debris will drop into damp soil that has not been calibrated correctly, Mold will then form on the trunk of your bonsai and slowly work its way up to your plant.
This mold will then feed off your plant causing:
- Declaration of the leaves
- Leaves falling off
- Flowers/fruit not arriving when scheduled
- Slowed plant growth
- Drooping or wilting branches
This can also cause the white powder to occur.
Non-pathogenic mold occurs in a similar way however can be more dangerous, not only to your plant but also potentially to any pets or even you.
How to avoid white powder mildew caused by mold?
To treat white powder mildew caused by mold, you would treat this in the same way as you would treat a scale infection or bug infection of any kind.
To get a full to-do list then check out my scale removal post here but to summarize:
- Remove your bonsai plant to avoid infecting other plants
- Put on a pair of gardening gloves
- Use 70% rubbing alcohol in a cotton ball swab to rub down your plant in all the hard-to-reach areas, (leaves branches, etc) removing the white powder.
- Wipe down the planter/plant pot and topsoil with rubbing alcohol in a tissue
- Mix a solution of 30oz of water, two tablespoons of liquid soap, and 1 cup of rubbing alcohol in a solution
- Pour this solution in a spray bottle
- Spray your plant thoroughly
- Leave to dry for 24 hours
Again to prevent any future infestation you will want to clean your plant like this at least once every two weeks.
A lot of mold-based infections your bonsai will have is because of overwatered soil (often the opposite problem of fungal white powder mildew) if this is the case you may want to repot your bonsai weekly or remove any debris daily from building up.
Once again, should your plant be too far gone with mold infections, consider taking it to a specialist bonsai garden center to treat.
Why is it important to treat white powder on bonsai leaves?
White powder mildew on bonsai leaves is important to treat as failure to do so can result in poorer health and even death for your bonsai tree. This will typically start with leaves discoloring, eventually falling off as the white powder slowly envelopes the rest of your plant.
What plant do species suffer from white powder more than others?
As bonsai trees are made up of thousands of different species, are there any breeds that suffer from white powder more than others?
Chinese and Japanese Elms plants are more likely to suffer from white powder than other bonsai species. This is mainly because of the number of leaves and fall under broadleaf varieties. They also have the susceptibility they have to dry topsoil.
This post was written by Fehed Nicass who has been passionate about bonsai for over 2 years. He currently resides in the Uk and works in sales.