White Spots on Japanese Maple: 7 Possible Causes & Solutions

Japanese maples, as decorative trees, require ample maintenance in order to maintain their aesthetic appeal. However, they are often susceptible to various pests, diseases, and harsh weather conditions that may potentially mar their beautiful foliage.

White spots are one of the common issues you’ll see on the leaves of Japanese maples.

White spots on Japanese maple leaves could be caused by leaf spot, which is a common disease, Phyllosticta, powdery mildew, a fungal infection, scale, mealybugs, bird droppings, or unfavorable weather conditions such as late spring frost.

Every one of those causes has a different set of symptoms and solutions. Read more to find out how to identify the real cause of white spots on Japanese maple leaves and what to do about it.

Make sure you also read my Japanese Maple Diseases and Pests guide for all the common pests and diseases that come with growing Japanese maples.

White Spots on Japanese Maple Leaves: Causes & Solutions

What makes white spots on Japanese maple leaves so tricky to diagnose and treat is that they’re common and can be caused by a wide variety of diseases, fungi, and bacteria.

Moreover, if the weather turns and sudden frost covers the tree in the late spring, that also could cause white spots to form on the leaves. 

Leaf Spot

Leaf spot is a common disease that can happen at any time during the spring or summer. It’s caused by different fungal spores.

Some bacteria and pathogens and even mites and insects might also be responsible for this disease.

The symptoms start as tiny white spots that might soon grow and turn yellow or brown. Infected leaves tend to fall off if the problem is not fixed in time.

Solution

If pathogens are causing leaf spots, avoid getting water on the canopy. Leaf spot is not a fatal disease, and in most cases, the infected leaves will drop on their own, and the foliage will regain its former splendor.

That said, if the infections are severe, you might want to remove the infected leaves if you can and spray the canopy with fungicides.

Phyllosticta

Phyllosticta is a type of fungus that is quite common in many gardens. It favors moist conditions, so you’ll often find infestations right during or after rainy periods.

The symptoms are usually small spots that grow and join together turning yellow in the process.

Although the infection is not fatal to the Japanese maple, it can impact the foliage and open the tree to other infections.

Solution

It’s always a good idea to treat the symptoms of Phyllosticta infections as soon as they appear on the leaves.

Apply a fungicide such as Ferbam, Captan, Dithane M45, or Mancozeb once every week or 10 days depending on the severity of the infection.

Improve ventilation, and avoid getting water on the leaves in the summer months.

Powdery Mildew

The fungus that causes powdery mildew prefers hot and dry conditions. It spreads through the wind although some strains are carried by the rain as well.

The spores overwinter on the leaves and start a new infection in the spring. It first appears as tiny white spots that turn gray as they join together to cover most of the surface of the leaf.

In severe cases, it will spread to the stems and branches. 

Solution

You can treat powdery mildew with a mixture of baking soda, dish soap, and water.

Both neem oil (find it here) and sulfur-based fungicides (here) show good results in eradicating the fungal infection without affecting the leaves of foliage.

If the infection is limited to a few branches, you can trim off the infected leaves or even cut the whole branch to prevent the spread of the infection.

Late Spring Frost Damage

There’s a reason deciduous trees shed their leaves and go dormant in the winter. The cold temperatures will kill any new growth and put the tree itself in danger.

Once the last frost is over and the weather warms up in the spring, only then would the tree come back to life.

However, an unpredictable late frost can wreak havoc with new growth. The young leaves may have a spotted appearance and will likely die.

Solution

You can’t control the weather, and you can’t always protect the Japanese maple against inclement frosty temperatures, though a frost blanket may provide some protection.

What you can do is pick the dying leaves and remove the ones with white spots on them. This will help the tree replace them faster.

Otherwise, you can let nature run its course. The affected leaves will drop on their own.

Scale 

Scales are tiny bugs with oval and flat bodies. They’re covered with a protective shell that’s usually brown, which helps them blend into the environment.

Since they’re vulnerable, they prefer to spend most of their time hiding under the leaves. They suck the sap and are hard to detect.

The only telltale sign of a scale infestation is usually the trail of honeydew they leave behind. The honeydew is fertile grounds for sooty mold, a common fungal infection.

Solution

Once mature, scales are hard to control. Your best option is to spray them with neem oil while they’re in the crawler stage.

You can also spray them with a mixture of rubbing alcohol, baking soda, and baby shampoo diluted in water.

Mealybugs

Mealybugs are a type of scale. They average less than a quarter inch long, and their body is covered with gray mealy wax. This wax layer protects them against many pesticides.

However, like other scales, during the crawler stage (when they are nymphs), their body is not covered with wax, which makes it easier to eliminate them. 

Solution

Natural predators of mealybugs such as ladybugs, lacewings, and mealybug destroyers offer an excellent and safe way to get rid of the bugs.

They feed on mealybugs even when they’re mature and hard to kill. You can also spray the nymphs with neem oil or other insecticides.

Bird Droppings

When birds do their business on the canopy of the Japanese maple, their droppings contain chemicals that could damage the surface of the leaves.

The problem with these droppings is that they can stay on the leaf until it finally shrivels and falls.

Other than the limited damage to the specific leaf that comes in contact with bird droppings, there’s no other damage to the tree.

Solution

You can hose the bird droppings off the canopy. That will prevent most of the damage to the leaves and keep the tree looking its best.

If the birds have nests nearby, you might want to remove the nests or relocate them somewhere else.

Tips for Keeping Japanese Maple Healthy

Care for the Japanese maple is ongoing from the moment you plant it until it establishes. Even after the tree has been established, you still need to provide care and maintenance to keep it healthy.

  • Mulch around the tree in the spring and summer to improve water retention.
  • Water it regularly to keep the soil moist in the summer.
  • If your summers are hot, choose a variety resistant to burn.
  • Use slow-release fertilizers to avoid root burn and stress from sudden growth spurts.
  • Use rich mulch such as compost to provide nutrients over time.
  • Watch out for signs of diseases and pest infestations, and treat them accordingly.
  • Once established, you can lightly prune them while dormant to maintain their shape.

Related Questions:

Are Japanese Maples Hard To Grow?

Japanese maples are quite easy to grow, especially if you have experience with other ornamental trees.

They need regular pruning of dead or diseased branches and mulching to keep the moisture in the soil during the hot summer months.

Test the soil, and provide any missing nutrients in the form of plant food supplements. 

How Long Do Japanese Maples Live?

Japanese maples have a long life span and can stay around for one hundred years. Their annual growth rate averages 1-2 feet.

Picking the right variety for your region is essential for keeping your Japanese maple healthy and preventing premature death.

Closing Thoughts

When you see white spots on the leaves of Japanese maples, look for pests such as scales and mealybugs or diseases such as leaf spot and powdery mildew.

Weather conditions such as late spring frost could also damage the leaves. Treat any diseases, and get rid of pests to keep your Japanese maple healthy and in good shape.

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