- David Hale
One of the most frustrating aspects of looking after bonsai trees can be dealing with pests. Scale, fungal infection, and insects infecting your tree are common problems that will affect all bonsai owners at some point. One of the most common pests we see in bonsai is spider mites, which can be hard to identify unless you're looking for them.
Let's look at how to get rid of spider mites on bonsai trees, as well as what they are and how you can spot them.
- What is a spider mite?
- Spider mites life cycle
- What spider mites do to plants
- What causes spider mites on bonsai?
- Signs of spider mites
- How to check for spider mites
- How to get rid of spider mites on bonsai
- Why do I keep getting spider mites?
What is a spider mite?
Spider mites are not actually spiders, they are mites. They are also known as the 'two-spotted mite' because you can see two spots on their back when viewed under a microscope.
Spider mites can be seen by the naked eye but are very close to microscopic. They have a stylus that they use to pierce plant cells and feed off the contents.
Spider mites life cycle
Spider mites are very fast to reproduce, which is one of the reasons they are such a significant pest. They pass through the following developmental stages: egg, larva, protonymph, deutonymph, and adult.
Eggs hatch 3 to 6 days after being laid and will be ready to reproduce after a further 4-9 days. This is important to remember because even if you remove all adult mites, eggs can hatch days later and continue the infestation on your bonsai tree.
How long do spider mites live?
Adult spider mites live for around 30 days, and it can take 8-17 days for an egg to become a breeding adult.
How spider mites spread
Spider mites can spread via a variety of routes. The most common way they can be introduced to your garden is from other plants, such as plants bought at a nursery. They can also spread via other routes such as on birds or animal fur.
What spider mites do to plants
Spider mites feed off the tree by piercing the cellular structure of an individual plant cell and sucking out the contents of that cell. The plant cell dies as a result of this, which on a large scale leads to health problems with your bonsai tree.
Spider mites specifically feed off chlorophyll, which is the green pigment in the cell. Chlorophyll is used in the process of photosynthesis to help capture UV rays and convert water and carbon dioxide into sugars (energy). Spider mites have a stylus that comes out of their mouth to pierce the cell wall and suck out all of the nutritious chlorophyll.
What causes spider mites on bonsai?
Spider mites thrive in warm, dry conditions. They become far more prevalent over the summer months, where heat, drought, and a reduction in relative humidity facilitate the growth of spider mite populations. Spider mites can also be a problem for indoor bonsai, where conditions are almost always warm, dry, and with low humidity. Spider mites also thrive in dusty conditions, which can be an issue for both indoor and outdoor bonsais if foliage starts to build up dust.
Signs of spider mites
Being able to identify and treat pests is an essential part of good bonsai care. The signs of spider mites will vary based on the plant affected and the severity of spider mite infestation.
Signs of spider mites include:
- Dulling of the foliage color
- Yellow of foliage
- Loss of vigor
- Fine webbing
What are the first signs of spider mites?
The first signs of spider mites are greying of the foliage or a general dulling down of the vibrancy in the green of the tree's leaves/needles. The tree may look generally duller or just not quite right, and it can be difficult at this point to work out what is wrong with the tree.
The reason the tree loses the intensity of its green color is that the spider mites are feeding off the chlorophyll in the leaves. Chlorophyll is the source of the green color, so as more of it is removed by the spider mites, the tree will start to become more and more grey and washed out.
When you first notice one of your bonsai trees is greying, it's a good idea to try and identify any spider mites early, as treatment now will be easier and more effective since the infestation will have had less time to establish itself. You can look for the presence of spider mites using the tap test.
Yellowing is another indication of a spider mite infestation in your bonsai tree. Yellowing from spider mite damage occurs as stippling. As with greying, the yellow discoloration happens because spider mites have removed chlorophyll from the plant cells. As they do this to more and more cells in one particular area, you will start to notice yellow spots appearing on leaves or needles. These blocks of yellow color will continue to grow as more damage is done to the foliage.
A reduction of vigor is a further sign that something is wrong with your bonsai, and when combined with other signs it can be a good indicator of a spider mite infestation. Your tree may slow down in growth or start to use less water, and if this happens you should check for spider mites.
What are signs of an advanced spider mite infestation?
A final sign of spider mites you need to be aware of is the presence of fine webbing. This shouldn't be confused with regular spider webs, which are very common on bonsai trees (spiders are a very positive part of a good ecosystem in your tree). Webbing from spider mite infestation is usually a late sign and indicates a severe infection with a large population of spider mites. Webbing will generally be seen between the base of needles or between leaf petioles, and is extremely fine.
Signs of spider mites on indoor plants
Indoor plants will show the same symptoms as outdoor plants when infected with spider mites. Signs include dulling of foliage color, yellowing of foliage, loss of vigor, and in severe infections webbing around leaves and needles.
Signs of spider mites on succulents
Succulents and tropical bonsai such as Jade show many of the same signs as other plants when they have a spider mite infestation, but since they have a different growth habit from other bonsai trees, they can show slightly different signs.
The biggest sign of spider mites on succulent plants to look out for is white or yellow spotting on the leaves/foliage. Foliage can be spotted like this due to a localized loss of chlorophyll, which is happening because spider mites are feeding off the chlorophyll in the plant's cells.
How to check for spider mites
The tap test, also known as the paper smear test, is probably the most accurate and sensitive test for spider mites, assuming you don't have a lab in your garden to analyze needles under a microscope!
To perform the paper smear test, all you need is a plain white piece of paper. Holding the paper under your bonsai, tap the branches and foliage above the paper. This will cause spider mites to fall from your bonsai onto the paper. If you have very good eyesight you may see some mites crawling around on the paper, but you may also see other beneficial critters that are living on your bonsai.
After you have tapped the branches above your paper, you need to firmly wipe your hand across the paper, 'smearing' any spider mites that may be there. You will probably not see or feel anything before you perform the smear, but if there are spider mites on the paper you will see red streaks where they have been crushed by your hand.
Streaks from spider mites will be red or brown, but you may see other colors such as black, green, or yellow. These could be other pests such as aphids or may be beneficial predator insects that are benefiting your bonsai.
Spider mite infestations will begin in a single, localized region of your bonsai. You need to make sure that you perform the tap test on all branches of your tree, otherwise, you may miss the presence of an infection.
How to get rid of spider mites on bonsai
Spider mites reproduce very rapidly, which can make them a difficult pest to treat. Dealing with spider mites requires a consistent application over some time to get the best results. Unhatched spider mite eggs can be resistant to certain treatments, so if we let those eggs hatch and start to build the population again we will be back to square one.
You can use chemical or natural approaches to tackle a spider mite problem on your bonsai.
How do you get rid of spider mites naturally?
Water eradication is a very good option if you identify a single tree or a small number of trees in your collection that have mild indicators of spider mite infestation. Using water eradication has the benefit of avoiding chemicals and miticides, which do not discriminate between good or bad organisms in your bonsai trees' ecosystem.
Spider mites do not cling to the plant matter very securely, so it is possible to knock them off with a strong stream of water from your hose. As well as physically removing mites, water will make the environment less favorable to spider mite growth, since we are cooling foliage, removing dust, and raising the humidity levels around the bonsai tree.
The key to this technique is consistency. Spider mite eggs will usually not be removed by the hose stream, so we need to come back every day to eradicate newly hatching spider mites on your bonsai. You need to do this for at least 7-10 days to make sure all eggs have hatched, and those hatched mites have been washed off the tree before they've had a chance to mature and lay new eggs of their own.
If you are choosing to try water eradication to treat a spider mite infestation, please be aware that there are some potential drawbacks if you misapply this technique. Firstly, drenching the foliage mass of your tree daily could lead to overwatering your bonsai. This could lead to issues with the health of the roots of the tree, which could be far worse than a spider mite infestation. Secondly, keeping foliage on a tree constantly wet can encourage the spread of fungal disease, so if this is already prevalent in your garden you may want to consider a different approach.
Spider mite control with chemicals
If you can't use water to treat your spider mite problem, or if you have a very heavily infected tree, you may want to consider using chemicals to kill the spider mites on your bonsai.
When choosing chemical treatments, you must choose one that is mite specific. Insecticides often target a variety of different bugs, but different organisms must be killed in different ways, so if you use a chemical that doesn't specifically target mites you are unlikely to address the problem and will probably do more harm to your bonsai by killing many beneficial insects that are living in the ecosystem.
Local garden centres or hardware stores will sell miticidal chemicals that you can use to treat your tree. Follow the label recommendations for application, and if your bonsai is particularly valuable you may want to test the chemical on a different tree first.
Spider mite control with neem oil or horticultural spray
Oils and soaps can be effective in killing spider mites on a bonsai tree.
Neem oil is the most popular oil used in the treatment of spider mites. Oils in general can eradicate insects by coating their breathing holes and suffocating them. Neem oil also has natural insecticidal properties that make it very effective in tackling pests in your bonsai tree.
The downside of using oils and soaps is that they can be phytotoxic, meaning they can be harmful to the tree's foliage. It's a good idea to try your oil/soap on a cheaper or less important tree of the same species to make sure it doesn't cause any harm, before applying it to any valuable bonsai.
Why do I keep getting spider mites?
There is a growing problem around the world of spider mites that are resistant to some chemical treatments. If you are treating your plants properly according to label recommendations and spider mites keep returning, you could be experiencing this issue.
Insecticide resistance in spider mites comes about when a small number of mites survive the initial treatment. They likely have a gene mutation that gives them resistance to that particular chemical. When they reproduce, all future generations will inherit that immunity.
As the cycle of treatment and survival continues, the mites become more resistant over time.
To combat this, you may need to consider using more than one chemical to treat your mite infestation. Using 2 or 3 different treatments on rotation, as well as a thorough water blast the day before chemical application to remove as many of the mites as possible, can help to ensure the entire colony is destroyed.
Should you cut off leaves with spider mites?
If you can identify leaves that are heavily infected with spider mites it can be good to prune them, however, most spider mites will be invisible to the eye and you are unlikely to be able to remove all mites by pruning alone. I would recommend one starting with water eradication, then moving to chemicals if required.
Can leaves recover from spider mites?
The damage to leaves caused by spider mites is not reversible. The leaves may still function to some degree, but not as well as they did before.
Do bonsai trees get spider mites
It is very common for bonsai trees to get spider mites. They are a pest that needs to be managed every year by those who live in spider mites hotspots.
Spider mites vs Soil mites
The main difference between spider mites and soil mites is where they live on the plant. Spider mites always colonize the foliage and leaves, while soil mites only live in the soil below the compost line.
Can spider mites live outside?
Spider mites live outside, particularly in areas that have dry, warm summers. They can also be found indoors on house plants and bonsai because the dry and warm conditions help them to thrive.
Are spider mites harmful to humans?
Spider mites are not harmful to humans or animals. They feed only on plants, and won't hurt people.
Do spider mites bite you?
Spider mites cannot bite you or harm you.
Do spider mites make webs?
Spider mites make very fine webs, which is one of the features that led to them being named spider mites. These are seen on plants with an advanced infestation.
Are spider mites real spiders?
Spider mites are not real spiders, they are mites. They are called spider mites because of their many legs and their ability to make webs, similar to a spider.