A healthy Japanese Maple tree can elevate your entire garden with its almost ethereal beauty. That makes it all the more heartbreaking to see one covered with bugs. While these aren’t the most pest-prone trees around, a few kinds of insects and mites may plague your Acer Palmatum (or A. Shirasawanum, or A. Japonicum). Presented below is our complete guide to spotting and removing Japanese Maple pests.
Sap-sucking parasites like aphids and scale insects can stunt your Acer’s growth and wither its leaves. Other Japanese Maple pests, including caterpillars and Japanese Beetles, can chew the leaves ragged. You can treat these pests with methods ranging from manual removal to chemical insecticides.
While it can be tempting to go for the strongest possible bug killer right away, sometimes moderation is key. Overly harsh treatments can further damage your Japanese Maple, leaving it even more vulnerable to pests and disease. In addition to helping you identify frequent pests of Japanese Maples, we’ll talk about safe ways to apply the most widely used treatments.
The 7 Most Common Japanese Maple Pests
Let’s review the usual suspects and how to recognize the crime scenes they create. Here are the bugs you’re most likely to find feeding on your Japanese Maple.
#1: Aphids
Symptoms:
Wilting, curling, discolored leaves. New growth may be stunted and shriveled. Honeydew (a sticky goo the insects excrete) on leaves and bark. Sooty mold — a dark gray-black fungus — may grow in the patches of honeydew.
Description:
Aphids are soft-bodied, sap-sucking insects that can come in a wide range of colors, including green, yellow, brown, red, and black. On average, they’re about the size of a pinhead, but they can get bigger as they feed and swell up. You’ll usually find them in large clusters, often near the ends of branches. An aphid is roughly pear-shaped and usually has two small hairlike tubes poking from its abdomen.
Aphids are sometimes accompanied and transported by ants, which “farm” them for the sugary honeydew they produce. They’re opportunistic bugs that will attack a wide variety of garden plants. Aphids usually aren’t deadly Japanese Maple pests, but a bad infestation can seriously derail your tree’s growth.
How to Get Rid of Aphids on a Japanese Maple
If you only see a few aphids, you can usually get rid of them by blasting them off with your garden hose. Or pick them off with your fingers and squish them. When your Japanese Maple is badly infested, you may need to spray the infested leaves and branches with insecticidal soap. See below for details on how to use this pesticide effectively.
#2: Spider Mites
Symptoms:
Dry, curled, crispy leaves. Affected foliage turns yellow or brown, often with patches of mottled scarring that make them look dusty. Wispy webbing between branches and on the undersides of leaves.
Description:
Spider mites are arachnids, not insects, and they’re so tiny that the individuals are almost impossible to spot on your Japanese Maple. However, you may be able to see them by shaking a leaf over a piece of white paper. The mites that fall off will look like tiny flecks of black pepper or paprika.
Their webbing is more recognizable. It often clings like a film over large portions of the foliage, and it may look dirty due to the mites and eggs stuck to it.
Spider mites are most active in hot, dry weather. They prefer to attack plants that are weakened by drought, so keep your Japanese Maple well-watered in the summer. That goes double for young, newly planted trees.
How to Get Rid of Spider Mites on a Japanese Maple
Like aphids, spider mites can often be repelled in the early stages of an infestation by hosing down the tree. Make sure to get the undersides of the leaves, which is where mites like to hang out. For more severe infestations, insecticidal soap may be a good idea. If that doesn’t work, try applying neem oil or horticultural oil (see below for details).
#3: Japanese Beetles
Symptoms:
Ragged holes in leaves. When beetle populations are high, leaves may be skeletonized, with no leaf tissue left between veins. Grubs can cause yellowing, browning, and dropping of leaves.
Description:
These notorious garden pests have shiny green heads and torsos with coppery wing casings covering their abdomens. Whitish fuzz sticks out from their sides under the wings. They’re about half an inch long. Adult Japanese Beetles are enthusiastic Japanese Maple pests. They tend to show up in swarms, rapidly chowing down on the foliage in a frenzy of eating and mating. They lay eggs in the soil that hatch into pale white grubs that damage the roots of grass and trees.
This damage can leave your tree looking forlorn, but it usually won’t kill a well-established Japanese Maple. Younger trees can be seriously threatened by Japanese Beetles, though. And if your Acer is already weakened by issues like sunburn or overwatering, a beetle attack could finish it off.
How to Get Rid of Japanese Beetles on a Japanese Maple
One simple treatment is to go out before sunrise and pluck the bugs off the leaves while they’re still sleeping. Dunk them in a bucket of soapy water to drown them. This is likely not workable for large Japanese Maples, but it’s great for dwarf varieties or younger trees. Insecticidal soap spray can be a good treatment for a bigger tree, and you can pour some predatory nematodes into the soil to kill the grubs.
Avoid fancy traps that lure Japanese Beetles with pheromones, which usually draw in more beetles than they kill. They’re worse than useless unless you find a spot that’s at least 100 feet from any plants you care about. On the other hand, geraniums make an interesting natural “trap”. The bugs like to eat them, but afterward, they’re paralyzed for hours, easy prey for predators and gardeners alike.
#4: Scale
Symptoms:
Wilting, undersized, discolored leaves. Honeydew and sooty mold on branches and foliage. Severe infestations can cause leaf loss and dieback of twigs and branches, thinning out the canopy.
Description:
Scale insects don’t look like insects at first glance. They’re completely immobile and covered in a tough, smooth shell, appearing as round or ovoid bumps on the bark. Many species of scale are camouflaged by brown or gray coloration, making them extra hard to spot. Others have a softer coating of whitish wax, and some species produce puffy white egg sacs.
Scale are voracious Japanese Maple pests that pierce the bark of the tree to drink its inner juices. They’re also stubborn and can be difficult to kill due to their protective coverings. Left unchecked, a scale infestation can severely weaken or kill a Japanese Maple.
One type of scale — the appropriately named Japanese Maple Scale — is particularly fond of munching on Acer Palmatum trees. This variety has a slightly curved shape like an oyster, with a whitish coating of wax over a purple-brown shell.
How to Get Rid of Scale on a Japanese Maple
If you catch them early, you may be able to scrape the scale off your Japanese Maple with your thumbnail. Drop them in a jar of rubbing alcohol to kill them. Then hose the tree down to knock off the tiny, mobile larvae.
Swabbing down the scale with rubbing alcohol can be a tedious but effective way to treat more serious infestations. Thoroughness is essential because only the bugs that make direct contact with alcohol will die. So make sure to get all of them! Another option is to treat your Japanese Maple with horticultural oil.
#5: Mealybugs
Symptoms:
Similar to scale — wilting, discoloration, stunting, and loss of foliage. Honeydew and sooty mold. Dieback of branches and twigs if left untreated.
Description:
Mealybugs are related to scale insects, and the damage they do is very similar. But unlike their cousins, mealybugs are mobile. They’re superb at hiding in even the tiniest spaces and particularly love targeting cracks and wounds in tree bark. That’s one reason it’s important to use proper technique when pruning your Japanese Maple.
Though they’re shaped much like scale insects, mealybugs are almost always covered in fluffy-looking white wax. If they’re infesting your Japanese Maple, it will look as though the tree is covered with small bits of cotton.
How to Get Rid of Mealybugs on a Japanese Maple
The treatment for mealybugs is similar to that for scale. However, if you’re going to swab them with rubbing alcohol, you’ll want to take extra care to get into all of the nooks and crannies where they could be hiding. Unlike scale, mealybugs can also be killed by insecticidal soap.
#6: Granulate Ambrosia Beetles
Symptoms:
Leaking sap and odd, threadlike white protrusions coming from holes in the bark. Stunted growth, delayed leaf appearance in springtime, and premature loss of foliage. Cankers (blisters of dead, gnarled wood) may form on trunks or branches.
Description:
You’re unlikely to see these nasty beetles because they bore into the wood of your tree and rarely emerge. Instead, you’ll notice the odd, pale “toothpicks” of sticky sawdust pushing out of the trunk. Ambrosia beetles eject them as they carve twisting tunnels or “galleries” inside the wood of a Japanese Maple. If you catch one of these bugs in a trap (see below), you’ll see a round-headed, reddish-brown bug about one eighth of an inch long.
Granulate Ambrosia Beetles, sometimes called Asian Ambrosia Beetles or Exotic Wood Borers, don’t actually eat wood. Instead, they infect trees with the Ambrosia fungus they feed on, which can be utterly lethal to Japanese Maples. It spreads stealthily below the surface, so gardeners who don’t spot the beetle damage can be startled when their tree suddenly drops dead.
How to Get Rid of Ambrosia Beetles on a Japanese Maple
Unfortunately, by the time the beetles have attacked a tree, it’s generally too late to do much about it. There isn’t a reliable cure for the fungus, so you just have to wait and see if the tree recovers. If not, remove it and destroy it. Your best bet is to keep your Japanese Maple healthy and be careful about introducing contaminated plants or wood into your garden.
You can also watch out for news about infestations in your area. If these beetles are moving in, you can purchase a funnel trap (or make one from an old soda bottle). It won’t protect your trees, but it will alert you when the beetles are active so you can spray your trees with a protective spray of permethrin.
Timing is key here — you need to apply as soon as the beetles begin showing up in the trap in the spring. Create a 0.5% dilution of the 38% permethrin concentrate and spray it over the trunk of your Japanese Maple.
#7: Vine Weevil
Symptoms:
Chewing damage around edges of leaves. Wilting, dehydrated leaves, foliage drop, and in severe cases, plant death.
Description:
There are two life stages to worry about with these Japanese Maple pests. The less dangerous one, which is also easier to detect, is their adult phase. Adult Vine Weevils are pear-shaped and about three eighths of an inch long, with bumpy black or gray bodies that may have orange-brown spots. They have long antennae poking out from their somewhat narrow heads.
The soil-dwelling larvae are much nastier. While the adults chew the leaves, the grubs strip tissue from the roots, often killing them outright. Heavy feeding can kill a young tree, and container Japanese Maples are particularly vulnerable. A Vine Weevil grub is short, fat, and white, with a small orange head. When disturbed, it will curl up in a crescent shape.
How to Get Rid of Vine Weevils on a Japanese Maple
Like Japanese Beetles, weevils can be plucked off and crushed with your gloved hand. You’ll have to go out at night with a flashlight to catch them, though. If you have potted Japanese Maples, it’s best to uproot them and search them thoroughly for grubs once you spot an infestation. You can drown them by dunking the roots in water.
If those methods don’t work, the nematodes we mentioned as a Japanese Beetle treatment should also kill Vine Weevil larvae when watered into the soil. As a last resort, you could treat your trees with a synthetic pesticide like imidacloprid. But be aware that this may also threaten beneficial insects in your garden. Neem oil, applied either as a spray or a soil drench, is a less dangerous alternative.
How to Use Insecticidal Soap for Japanese Maple Pests
Insecticidal soap is a useful tool for killing soft-bodied insects like aphids, spider mites, and mealybugs, but it carries a risk of phytotoxicity. In other words, it can damage or kill leaves under some circumstances.
Japanese Maples are among the plants known to be sensitive to insecticidal soap. Some guides will insist you should never use this treatment. Others, including some professionals who grow these trees for a living, recommend it enthusiastically.
The most likely explanation is that some varieties of Japanese Maple are more sensitive than others. We’d suggest saving the soap for severe infestations and testing any product on a few leaves before spraying it over the whole tree. Wait a day or two to see if the leaves show signs of discoloration or wilting before proceeding. If they do, look for an alternative method.
Apply insecticidal soap during the evening or early morning since heat, humidity, and direct sunlight increase the risk of phytotoxicity. Never use it when the temperature is over 90oF or the humidity is above 90%. And if your Japanese Maple is in full sun, you may want to hang some shade cloth. You should also avoid using insecticidal soap while a Japanese Maple’s leaves are still unfolding and expanding in early spring.
When spraying, target the infested areas rather than spraying indiscriminately all over your Japanese Maple. (But do coat the affected limbs thoroughly, including the undersides of leaves.) Remember, even if you don’t exterminate every single bug, cutting down the population may be enough to let your tree fight them off. It may take multiple treatments with insecticidal soap to get rid of your Japanese Maple pests. If the weather isn’t rainy, it’s probably best to rinse your tree off between applications.
Can You Make Your Own Insecticidal Soap?
It’s possible to make a DIY version of insecticidal soap. You’ll be taking a slightly bigger risk than you would with a product that’s been tested for safety, but it will definitely be more cost-effective. It’s especially important to first test your homemade bug killer on a small portion of the plant.
To make homemade insecticidal soap, mix two and one half teaspoons of gentle liquid castile soap in one gallon of water. You can include a tablespoon of vegetable oil to help the soap cling to the leaves, but it’s not necessary. If your tap water is especially hard, use distilled water instead.
Do not use anything labeled as dish detergent. These products contain grease-cutting chemicals that are much harsher on the leaves.
Shake the mixture up thoroughly. Then transfer some to a spritz bottle or garden sprayer and use it as we’ve described above.
How to Use Horticultural Oil for Japanese Maple Pests
Another useful pesticide that generally has little effect on helpful insects is horticultural oil. Where insecticidal soap works by dissolving the cell membranes of soft-bodied insects, horticultural oil coats and suffocates their pores. This makes it good for use on armored scale, which resists insecticidal soap due to their tough shells.
You can usually buy horticultural oil concentrate and dilute it in water to spray it on your Japanese Maple. This means a single batch can last a while. For Japanese Maples, choose an oil with a 92% or higher UR rating; this indicates that it’s highly refined and less likely to harm sensitive plants.
If you’re applying oil when your Japanese Maple is dormant, you can use a concentration of two to three percent. Your tree is more sensitive in summer, so limit it to a one percent concentration.
Test on a small part of the tree first, and don’t apply horticultural oil when:
- Your Japanese Maple is drought-stressed
- Temperatures are above 90oF or below 50oF
- You’re expecting a freeze overnight
- The tree is in bloom (otherwise, you could harm pollinator species)
- Humidity is above 90%
- Your Japanese Maple is in full sun
- The leaves are first emerging
Spray your diluted oil over the entire tree, coating it thoroughly. Make sure to get both the upper and lower surfaces of the leaves. As with insecticidal soap, you’ll probably need to repeat this treatment a few times, especially for scale. Check the label to see how long you should wait between applications, but it’s usually best to leave at least four to five days.
Can You Use Neem Oil for Japanese Maple Pests?
Neem oil is a natural tree-based oil that sees a lot of use as a pesticide. Not only can it smother insects, but it also appears to disrupt their digestive and reproductive cycles. Can you use it for Japanese Maples?
Once again, the answer seems to depend on who you ask. Some insist that neem will fry your tree’s leaves to a crisp, while others say they’ve used it without ill effects. Our guess is that, as with insecticidal soap, there’s some variation between Japanese Acer cultivars. And many of the worst reports likely come from those who used neem oil without adequate precautions.
Test your neem oil on a few of your Japanese Maple leaves to check for sensitivity. Wait at least a few days before concluding that it’s safe. Like the products above, you should avoid using neem in hot, humid, or sunny weather. Spray neem oil over your Japanese Maple in the evening, minimizing the risk of phytotoxicity and damage to beneficial insects.
Keep in mind that neem oil may help control pests on Japanese Maples but often doesn’t eliminate them completely. You may want to pair it with methods like manual removal and spraying the tree down. Also, always buy pure cold pressed neem oil, rather than “hydrophobic extract of neem oil”. The latter is a derivative product that lacks azadirachtin, the active ingredient that gives neem its punch.
How to Prevent Japanese Maple Pests
Getting rid of bugs on your Japanese Maple is all well and good. Preventing them from moving in is even better. If you can avoid infestations on your Japanese Maple, you may never need the rest of this article.
The absolute best way to prevent pests is to keep your Japanese Maple in good overall health. Strong, thriving plants have their own natural defenses against bugs. But conditions like drought, root rot, and sun scorch can reduce your tree’s ability to fight off pests. Creatures like spider mites and mealybugs are great at sniffing out stressed and weakened plants.
So keep your Japanese Maple pest-free by helping it grow strong. If you need advice, we’ve got detailed articles covering many aspects of Japanese Maple care, including:
Increasing your yard’s biodiversity can also be a winning strategy. A thriving ecosystem that contains lots of natural predators for Japanese Maple pests is safer for your trees.
Certain tasty herbs, such as mint, dill, and fennel, attract helpful insects as they grow in your garden. Some ornamentals, like zinnias and daisies, can do the same. It may also be helpful to leave a few “wilder” patches where leaf litter and wildflowers can provide shelter for ladybugs and other predatory species. This guide contains even more tips on luring beneficial insects to your garden.
Finally, you should be careful to inspect any new plants for pests before planting them. Many nasty bugs travel by hitchhiking on cultivated plants. If possible, you should try to quarantine every new purchase for a month before introducing it to your landscape.
Final Thoughts
While seeing something attacking your prized Japanese Maple can be worrying, remember that a few pests aren’t likely to do lasting harm. The occasional parasitic bug is just a part of life for plants in the great outdoors. If your tree is healthy, most Japanese Maple pests should be pretty minor threats.
If you do run into a severe infestation, the methods above should help your tree get through it. Don’t forget that it’s normal to need multiple applications of any pesticide, though you should give your Acer a few days to rest between sprays. You may also want to vary between different treatments in case the bugs are resistant to one. With patience and thoroughness, you should be able to free your Japanese Maple of pests using the tips we’ve included here.