Acer trees are a popular and beautiful plant to grow in yards and container gardens.
It is important to know about the problems with Acer trees and how to prevent or remedy them.
Problems with Acer trees usually stem from watering issues, fungal infections, pests, and soil issues. Hot, freezing and high wind climate conditions can also negatively impact an Acer tree’s health. Acer trees should be planted in partially shaded and sheltered areas, given adequate water and nutrients, and treated immediately for any fungal infections.
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17 Problems With Acer Trees And What To Do
Acer trees, also known as maples, are deciduous trees or shrubs that have colourful autumnal foliage. They can vary in size, and many species of this woody plant are suitable for container gardening in communal gardens.
Acer species include maples such as the following:
- Japanese maple (Acer palmatum)
- Field maple (Acer campestre)
- Norway maple (Acer platanoides)
- Sycamore maple (Acer pseudoplatanus)
- Boxelder maple (Acer negundo)
These trees can be easy to grow, yet are susceptible to problems related to disease, weather, environment, growing conditions, and overall care.
This article will describe these problems and what you can do to help your Acer tree grow and thrive.
1. Climate
The field maple Acer is the only native tree in the United Kingdom. Other species are considered non-native and the overall climate can affect the ability of an Acer tree to thrive.
Climate conditions that negatively impact Acer trees include:
- Direct sunlight: dries out the leaves and soil
- Hot climates: dries out the leaves and soil
- Freezing climates: turns the leaves black or brown, resulting in decay
- High winds: exposure to high winds makes the tree lose leaves and dry out
What To Do
Acer trees should be planted in partially shaded areas and sheltered from high winds. While Acers can grow in full shade, the leaf colour may not be as vibrant.
A windbreak, fencing, or companion plants can be installed around an Acer tree for sheltering.
Soil should be kept moist, but not oversaturated. Potted Acers should have drainage holes on the bottom of the pot.
Acers can be wrapped with an insulating material, such as fleece or cardboard, to protect them from freezing and frost damage.
It is not recommended to bring potted Acers from freezing outdoor climates to warm indoor ones. The quick change is likely to shock and kill the plant.
If sections of the tree have died, prune only the dead material in warm conditions. This prevents open points that are exposed to freezing temperatures.
2. Leaf Scorch: Environmental
If leaves on an Acer tree turn brown, dry up, curl up, shrivel, or the lower branches are dying, leaf scorch may be the problem.
Beginning signs of leaf scorch may appear as leaves with colour, yet the veins and leaf edges are brown.
Leaf scorch is typically the result of dry windy conditions, drought, direct sunlight and heat, waterlogged soil, or exposure to frost.
Environmental leaf scorch is considered “abiotic”, provoked by non-living environmental factors.
What To Do
The Acer tree should be placed in the proper climate as mentioned above.
This includes protection from full sun, protection from high winds and freezing temperatures, and adequately watered soil. Mulch can be used to retain moisture around the base of the tree in drought conditions.
Dead parts can be pruned off of the tree in warm weather.
3. Leaf Scorch: Bacterial
Bacterial leaf scorch, known as biotic or marginal leaf burn, is the result of a pathogenic bacteria called Xylella fastidiosa. This bacteria invades the inner tissues of the plant, restricting water flow.
Scorching in this case appears unevenly on leaves with an irregular shape. It will look like red or yellow bands of colour between green and brown patches.
In more severe cases, the leaves will brown and curl up, dropping off, like they do with environmental leaf scorch.
What To Do
The condition will progressively worsen over several years, and unfortunately, this is a fatal disease for Acer trees. There is no cure since the bacteria has spread throughout the internal structure of the tree.
Professional diagnosis through laboratory processes can diagnose this bacterial infection.
The injection of special antibiotics, adequate irrigation, and mulching can slow the spread down, but ultimately the tree will eventually need to be professionally removed.
4. Over-Watering And Excessive Moisture
Plants need water to thrive, however too much water or moisture is harmful. This includes overly rainy conditions or waterlogged soil.
Too much water can lead to conditions such as root rot or the development of damaging fungal diseases.
Leaves may turn yellow, grey, or brown while curling inwards. Leaves may drop prematurely.
What To Do
If root rot or fungal infections have dominated the plant, likely, the plant will not survive.
Therefore, it is important to make sure the plant does not constantly “sit” in water. If the soil appears wet looking all of the time, it has too much water.
Potted
Potted Acers should have drainage holes at the bottom. Typically, they should be watered until the top surface appears wet. As time passes during the day the surface should dry out.
Generally, in hot weather, a potted Acer needs watering once a day. Stick your finger in about 1-inch deep, and if it is still wet, do not water again until this top layer is dry
Ground Planted
Dense clay soils will hold onto water more readily.
Amend the soil around the tree by adding horticultural grit or sand, shredded bark, or compost. In some cases, the tree may need to be transplanted.
Contact an arborist for the best way to fix soil conditions for ground-planted trees.
5. Root Rot
Root rot is a fungal infection as a result of overwatering. Various kinds of fungi grow in wet conditions. When the root system is affected the tree will struggle and eventually die.
Additionally, this fungi can spread to other plants, if you transplant a tree with root rot.
The following signs of root rot can be observed:
- Cankers (sunken lesions) on branches and trunks
- Mushroom-looking growths protruding from the base or on the trunk
- Dying branches
- Wilting and sparse foliage
What To Do
If there is constant rainfall, overwatering can be an issue that is hard to control.
You can amend the soil with sand to help improve drainage conditions. Potted plants can be moved to an area with shelter, such as underneath roof overhangs.
Potted trees may be able to be saved if there are some healthy roots left. Remove the tree from the pot and use pruning shears to trim rotten parts off.
Keep in mind that if you do not fully remove all rotten parts, the fungus can spread to the healthy roots. The tree will need completely new soil.
The pot should be thrown away or disinfected with a mild bleach solution and rinsed clean. The pruning shears should also be disinfected after use.
Avoid spreading the contaminated soil with your shoes or gardening gloves to other parts of your yard.
If a ground-planed Acer has been afflicted with root rot, professional removal will need to take place. Generally, new plants should not be planted in this infected soil.
To prevent root rot from occurring, the tree mustn’t be allowed to sit in water or become overwatered as mentioned above.
6. Under-Watering
While overwatering is a great concern for Acer trees, under-watering can cause problems too.
If you stick your finger into the soil and it is completely dry (nothing sticks to your finger) and leaves are browning, your tree may be in drought conditions.
What To Do
Thankfully, drought conditions can be improved easily with some care as long as the issue is addressed at the first signs of drought.
Potted plants have less soil than ground-planted ones, and typically need watering once a day in hot climates.
The top layer should remain moist and excess water will come out of the drainage holes. Once the top layer (1-inch) is dry to touch, then it can be watered again.
Ground Acers can be watered once a week. In times of drought, consider watering it daily, but watch for signs of overwatering.
If water pools at the base, restrict watering until it dries out again. Put down a layer of mulch to help hold moisture around the base of the tree.
7. Honey Fungus
Honey fungus (Armillaria) can affect woody plants such as Acer trees. It naturally grows, typically starting in autumn. It is commonly mistaken as root rot.
Acer trees with honey fungus will have decaying roots and fungal growth underneath the outer layer of bark and at the base. Afflicted trees will also have pale and small leaves and dying branches.
Eventually, the root system becomes so weak that the tree can topple.
What To Do
Much like root rot, the tree will eventually die.
The affected plant will need to be fully removed so that the infection does not spread to nearby plants.
The fungi spreads underground with root-like structures called rhizomorphs extending as deep as 45 centimetres down.
Professional arborists will remove infected soil, and then insert plastic into the ground (45 centimetres deep) to quarantine the area.
The soil can be checked after 8 months or more to see if the fungus has died off.
If it has, then the area can be used for planting again.
8. Powdery Mildew
This type of fungal disease thrives in humid climates.
It appears as a white powder on the leaves. The undersides of the leaves may be brown.
Fortunately, it is not lethal to the tree.
What To Do
Environmental humidity cannot necessarily be resolved, but consider watering your tree less often. The white powder can be wiped off by hand (wearing gloves).
Natural and chemical fungicides can be sprayed on the leaves, which include the following:
- Neem oil spray
- Equal parts of baking soda, vegetable oil, and dish detergent mixed into 4 parts of water
- Commercial products labelled for use on Acer (maple) trees to treat powdery mildew
9. Verticillium Wilt
This kind of fungus thrives in soils, staying dormant until it finds something for it to grow on, such as Acer trees. In periods of hot and dry climates, this fungus thrives.
Verticillium wilt often appears asymmetrically on one side of a tree, presenting as leaf loss, stunted growth, or yellow and wilted leaves.
What To Do
If you address this problem at the first signs, it can be resolved. If left untreated, it will eventually kill the plant.
The Acer tree needs adequate watering and shade. Use a fertiliser that is low in nitrogen and high in phosphorus. Phosphorus promotes healthy growth and helps the tree to convert nutrients into usable energy.
Prune dead or dying branches. Make sure to discard these into sealed plastic bags to avoid spreading the fungus to other areas. Disinfect gloves, shoes, and pruning shears afterwards.
More extreme attempts to kill off the fungus can be done by tilling and watering the top 15 centimetres of soil. Then cover it with a clear, plastic tarp in full sunlight.
The hot sun concentration may kill the fungus over time. Keep in mind that the tree still needs water to avoid drought issues.
10. Sooty Mould
This fungal disease thrives in response to a sugary, honeydew, sticky substance that is secreted by some insects, such as aphids and scale. Generally, this mould occurs in conjunction with a pest problem.
This mould appears as dark, threadlike grimy growth, appearing like a layer of soot all over the tree and leaves.
What To Do
To get rid of sooty mould, you have to get rid of the insect pests (more on that below).
Then the mould can be washed off of the tree or will rinse away in the rain. Neem oil can also be used to kill off the fungus.
11. Insect Pests
Insect pests such as aphids, scale, pear thrips, and mites can invade an Acer tree.
Depending upon the insects you may see sooty mould or leaves covered with velvet patches of fungi, raised bumps (pimples), or worm-like protrusions.
Leaves may become discoloured from insect eggs and feeding larvae.
What To Do
Extensive insect damage can kill trees, so it is best to remove them as early as possible.
Commercial and natural pesticides can be used. Spray on both sides of the leaves.
Natural options include the following:
- Garlic spray: Mix a few tablespoons of garlic puree in with hot water. Allow it to marinate overnight in a covered container. Strain it, and then add the liquid to a spray bottle.
- Pepper spray: Boil 1 gallon of water with 3 teaspoons of hot pepper flakes. Let it simmer for 15 minutes. Allow the mixture to marinate overnight in a covered container. Strain out the pepper flakes, and then add the liquid to a spray bottle.
- Neem oil: Mix 2 tablespoons of neem essential oil, 1 tablespoon of castile soap, and 2 litres of water. Pour into a spray bottle.
- This can be found commercially. It is an essential oil that can treat fungal infections and deter pests on plants.
- Soapy water: Add 1 or 2 tablespoons of soap to a water-filled spray bottle. Shake before spraying.
- Castile soap works best since there are no additives that could be harmful to plants.
- Vinegar spray: Mix one part vinegar with three parts water in a spray bottle. Consider spraying the vinegar only on the bark portions of the tree to protect the leaves.
- Vinegar deters aphids, but keep in mind that it can kill sensitive vegetation including leaves.
Synthetic pesticides are also an option. Consider using these as a last resort since they can be unsafe to use around other vegetation (especially edible ones) and pets, and can soak into groundwater sources.
12. Wildlife Pests
Rabbits and squirrels in particular love to munch on Acer tree bark for nutrition as well as to grind down their teeth.
This nibbling stresses the trees out, making some appear in poor health with damaged bark.
What To Do
Place chicken wire netting or metal sheeting around potted Acers and the trunks of ground trees.
Metal sheeting in particular creates a slippery surface that squirrels can’t climb. Install it to extend about 1 metre high.
Make sure that you do not severely tighten the sheeting so it prevents the tree from growing. It should be adjusted each year to allow space for growth.
A pepper spray as mentioned above can deter rabbits and squirrels. Spray it around the base of the tree.
Hanging shiny and reflective objects from the branches may scare rabbits and squirrels away. However, they may get used to them over time and no longer see them as a threat.
Lastly, you can offer feeding stations that rabbits and squirrels might prefer over the bark of your Acer trees. Keep in mind that this may invite other pests such as snakes and mice to your property as well.
13. Harmful Pruning
The pruning of an Acer tree should be reserved for removing diseased, damaged, or dead branches and leaves.
Pruning it can be done for aesthetic purposes but take care to not remove too much. This stresses trees out, and they may struggle to grow or survive.
What To Do
Stick to pruning a third or less of a tree every 3 to 5 years.
If you over-prune a tree, be patient, regrowth takes time. New growth may not occur soon or quickly, but if the tree is healthy it will sprout more branches eventually.
Give the tree optimal growing conditions with adequate watering, nutrition (fertiliser), and mulch.
14. Potting Issues
An Acer tree can struggle to thrive in a pot that is too small and without adequate drainage holes.
What To Do
An Acer should be in a pot that is at least double the size of its root system. This means that an Acer tree will likely need to be repotted every few years as it grows.
A pot should also have drainage holes to allow unneeded water to flow out. This helps to keep fungus and root rot away.
15. Fertilisation Issues
Generally, Acer trees can get nitrogen, phosphorus, and potassium (NPK) from the soil to grow well. However, if any of these are lacking, an Acer tree will struggle to thrive.
You can do a soil test using a purchased kit to find out the levels of each nutrient.
Fertiliser can remedy any deficiencies. Keep in mind though, that if you over-fertilise your tree that can cause damage as well.
Over- or under-fertilisation will present as stunted growth, leaf scorch, soft stems, leaf decay or discolouration, or dropped leaves.
What To Do
- Use commercial fertiliser according to instructions and formulated for your species of tree.
- Avoid using fertiliser on drought-stricken trees as this can cause a concentration that is too high.
- Opt for natural fertilisers, such as seaweed, manure, fish, and bone meal, which tend to offer nutrients without increased risk of over-fertilisation.
- If the tree is over-fertilised, carefully prune any affected areas. Stop fertilising it and give the tree time to recover.
16. Poor Soil Conditions
In addition to obtaining nutrients from the soil, Acer trees grow well in slightly acidic and sandy soil. This type of soil retains and drains water to keep the Acer tree adequately hydrated.
If the soil is too alkaline, then an Acer tree may have leaves with chlorosis (insufficient chlorophyll) and deficiencies in manganese, zinc, and iron.
The leaves may appear pale green or with yellow tips. These issues can lead to the death of the tree.
What To Do
Use loam-based compost with Acer trees, which are balanced in composition and nutrients.
Use mulch around the base of the tree to retain moisture and boost its growth.
Consider using fertiliser, as mentioned above, if the tree does not improve in its health after a few weeks.
Additionally, a foliar spray with iron chelate or iron sulphate can be sprayed directly on the leaves.
17. Transplantation Stress
Small Acer trees can be moved to different locations since their root systems are not as established as larger, mature trees.
Keep in mind though, that transplanting trees can induce shock and death as it is placed into the new soil.
What To Do
To properly transplant a tree, do the following:
- Maples become dormant when not actively growing. Wait until late autumn or early spring (before budding) to move it.
- Dig a wide girth around the base of the tree to avoid disturbing the root system.
- Wrap the root ball in burlap to hold it in place.
- Dig a new hole that allows a wide and deep girth to accommodate the root ball.
- Make sure the new spot is sheltered from the wind and direct sunlight.
- Consider transferring some of the old soil into the new spot if it is healthy and fungus-free.
- Remove the burlap covering and put the Acer tree into the new hole. Add water and mulch. Wait to fertilise to avoid “burning” the root system.
- Use supportive ropes and hooks to keep the tree upright, if necessary.
- Water daily and watch for signs of struggle.
If in doubt, contact a professional.
Prevention Tactics
You can implement several things to prevent and give your Acer tree a healthy life.
Do the following:
- Plant it in slightly acidic soil with some sandy composition.
- Potted Acers should be in pot diameters that are double the size of their root systems.
- Be prepared to increase the size of the pot every few years.
- Pots should have drainage holes.
- Water an Acer tree, taking note not to over- or under-saturate the soil.
- Use mulch in hot climates to help retain moisture in the soil.
- Acer trees should be in partially shaded and sheltered locations.
- Reserve pruning for damaged parts.
- Contact an arborist to give your tree optimum care
In Conclusion
Acer trees are prone to decay and death from fungal infections, insects, wildlife, and more.
With a little bit of care, Acer trees can provide many years of beautiful foliage for people to enjoy.
Taking preventative steps can protect Acer trees from becoming damaged or dying. This includes providing it with well-draining soil that retains moisture, yet drains excess away.
Acer trees also need partially shaded and sheltered locations to avoid issues from hot, freezing, and windy weather.
Pests and some fungal infections can be treated. In cases where there is root rot, contagious fungal infection, or extensive damage, the tree may need to be completely removed.
=> Need a tree taken down? click here and we’ll put you in touch with local tree surgeons who can provide up to 3 quotes for free.