The Japanese blueberry tree is a gorgeous evergreen tree native to Japan and China that has gained a lot of popularity in countries across the world, especially in the United States. While they are well-liked and very hardy, they still come with their own set of potential problems.
The most common issues with Japanese blueberry trees are leaf rust, chlorosis, sunburn, pest infestation, and sooty mold. Prevent these issues by limiting pruning to the end of February and mid-March, which keeps the tree branches safe from issues that typically happen during warm weather.
Reading the rest of this article will prepare you for the various problems that you might have with your Japanese blueberry tree. Thankfully the tree is generally disease-resistant, but it can still come into trouble if overwatered or not given enough sun.
Why Do People Love The Japanese Blueberry Tree?
Japanese blueberry trees are very beautiful and beneficial additions to your yard. They can grow up to 30 feet wide and 40 feet tall but can be pruned into many different shapes. Their leaves are a rich, deep green that occasionally turns red before falling. They bloom the prettiest white flowers during spring.
These trees are attractive to birds and butterflies, which makes them pleasant additions to the yard for more than just you.
The best part about the Japanese blueberry tree is how easy it is to take care of. They require no maintenance if you plant them in the right conditions (discussed below). However, many people prune and fertilize the tree to maximize its beauty’s potential.
People also like them because it’s hard for them to catch a disease, but it is possible. The most frequent ailment you’ll see on the blueberry tree is sooty mold, which I’ll talk about later.
Prime Environment Japanese Blueberries
Japanese blueberry trees are generally very hardy and can withstand drought once they are established. However, they won’t reach their maximum potential unless you put them in the right place with the right soil and conditions.
Japanese blueberry trees should be planted in zones 8 to 11. They enjoy a full sun location and soil that is well-drained and rich in nutrients.
If you have a Japanese blueberry tree, you should water it once a week during the summer months, and twice a week if it is extremely hot. The tree should get 15 to 20 gallons of water each week during its first two growing seasons. You want the root system to become fully established during this time. During its third growing season, you can begin watering it as needed. Don’t allow any standing water to form near the tree.
Experts suggest fertilizing your tree three times a year, in spring, summer, and fall. There are several fertilizers available, but I recommend Jobe’s 01660 Fertilizer Spikes Tree & Shrubs because they release fertilizer slowly into the soil so it doesn’t overwhelm the tree. Place these spikes along the dripline, one per every three feet of height of the tree.
Problems That Can Arise With Japanese Blueberry Trees
You have spent so much precious time and money on maintaining your beautiful blueberry tree that it is no wonder why you’ve become frustrated if you experience a problem with it.
Luckily, Japanese blueberry trees are quite hardy and relatively disease-resistant. Their problems are few, but they require care to keep these problems at bay. If you have noticed any of the issues below, don’t worry, we can fix them!
Normally, the leaves of the Japanese blueberry tree will fall after 2-3 years and be replaced by new leaves. The tree naturally sheds a lot of leaves and berries, but there is a problem if it is excessive and the branches are starting to become bare.
First things first, look at the color of the leaves that have fallen. Do they have reddish-brown spots? If so, that may be leaf rust. Read on further to figure out what to do if you’re dealing with leaf rust.
A lot of leaves will fall off if the tree does not have good enough drainage or it is not getting enough nutrients. If you notice standing water near your tree or hard, compacted soil, you probably have poor soil drainage. If you haven’t fertilized your tree since planting it, it may be lacking nutrients.
To improve the soil drainage around your tree, start by mixing compost into the soil. It will create more air pockets for water to drain. You should add 3-4 inches of compost every year to greatly improve drainage.
Apply a fertilizer every spring, summer, and fall to keep strong leaves growing and your tree nourished. This will create the best possible environment for it to grow full and tall.
Tree Tops Have Begun Dying (Sunburn)
If you notice the top of your blueberry tree has started to die off leaving bare branches sticking out above the leaves, there are two reasons why this has happened.
Japanese blueberry trees are thin-barked, so they are prone to sunburn. The part of the tree that is sunburned will die and stop sending nutrients to the leaves and branches above it. You can usually see where the damage has occurred by looking at the tree trunk right below the dying area.
You will notice sunburn on the side that gets the most sun by its discolored bark. This happens because the top of the tree wasn’t shaded enough by the canopy. Cut off the dead branches during winter and put a burlap sack over the top of the tree to shade it until new growth appears.
Another reason the tops of your blueberry tree are bare is an invasion of borers. Borers are wood-chewing insects that burrow into tree trunks and feed on the inner layers. They are usually beetle or caterpillar larvae. If they bore into your blueberry tree, they may have caused damage to the trunk, which means the top of the tree has been cut off from water.
Check for this type of damage by inspecting the trunk just below the bare branches. The bark will come off easily, especially if it’s facing the most sunlight. The borers will have burrowed right underneath the bark.
You can’t reverse the damage caused by borers, but you can apply insecticide to the tree’s soil once a year to keep them from coming back. Prune back the dead parts of the treetop during winter and be careful to leave proper canopy shade to the living branches below.
Anytime you are pruning off the dead parts of the top of the blueberry tree, you want to keep the exposed branches from getting sunburned. Like I said before, you can put burlap sacks over the tops of the tree to provide shade. You can also paint diluted latex paint over the exposed tree branches to lower the surface temperature and allow for new growth.
The Tree Canopy Is Thinning
Excessive shedding of leaves is a cause of concern for your blueberry tree. You’re frustrated at the canopy thinning in your Japanese blueberry tree, but you don’t know what caused it.
There are a couple of reasons that may explain why the canopy is thinning on your tree. The first reason could be that your tree is not getting enough water. If you’re in a desert area or somewhere with excessive heat, be very careful to water your blueberry tree often!
If your tree isn’t getting enough water, the leaves will thin out and the inner canopy will be exposed to the sun. Like I said before, Japanese blueberry trees can get sunburned. Taking special care to water the tree enough so it doesn’t get scorched is important if you want to have this type of tree in a hot and dry climate.
Another possible reason the canopy is thinning is that the areas that are becoming bare are not getting enough sunlight. Japanese blueberry trees will only thrive if they are getting enough sunlight, so the areas that don’t will suffer. This happens a lot when they are planted up against a fence.
If your blueberry tree is getting enough sun and water and it still is losing a lot of leaves, then you might have other trees or Japanese blueberry trees too close to it. If the tree’s roots are competing for resources, then it might not be getting enough nutrients to keep the leaves going.
Chlorosis occurs in a Japanese blueberry tree when the soil doesn’t have enough iron in it or the soil’s pH levels are too high. If it is severe and combined with dry weather, then the leaves can be seriously scorched.
Generally, the soil will have enough iron in it. However, if the soil doesn’t have a pH level higher than 6.5, it won’t be able to absorb the necessary iron. Iron is needed for the leaves to produce chlorophyll, so the first thing you’ll notice with this disease is that leaves are lightening in color and turning yellow. If it becomes severe, the yellowing leaves will fall off and branches may die back.
Factors that can make the chlorosis worse on your blueberry tree are overwatering, soil salinity, phosphorous content, concentrations of zinc, magnesium, and copper in the soil, soil temperature, and root damage.
The first thing you should do if you suspect chlorosis is to test the soil’s pH level. Japanese blueberry trees prefer soil that has a pH level between 6.1 and 7.3. If the pH level is too high, you know you’re dealing with chlorosis.
As a quick fix, you can use a foliar iron spray to speed up the process of healing your blueberry tree. Try using a chelated liquid iron spray like Southern Ag Chelated Liquid Iron to get quick results on your blueberry leaves. Apply it directly on the leaves and you’ll see results within a couple of days.
The foliar spray will only provide nutrients to the leaves themselves and doesn’t do anything to correct the problem in the soil that started the chlorosis in the first place, so only use it as a spot treatment.
To fix the soil, create a mixture of equal parts ferrous sulfate and elemental sulfur. I highly suggest using Monterey LG7115 Dr. Soil Acidifier Granules for this job. Add 1 cup of the mixture to the soil of your Japanese blueberry tree and water it thoroughly (do not overwater!) to reach all of the tree’s roots.
The foliar spray will have an almost immediate effect on the leaves, but don’t expect the entire tree to recover from chlorosis instantly. You will notice the changes in the next growing season.
Sooty Tree Mold Caused By Pests
Sooty mold, also known as black silt, is one of the very few diseases that can affect a Japanese blueberry tree. You’ll recognize it by the ugly black shadows and patches it creates on leaves, almost as if it were covered by the ash of a nearby campfire.
Luckily, sooty mold is usually harmless to your tree, but it can make the tree unpleasant to look at if too much of the black mold builds upon the leaves. The buildup can block the photosynthesis process too, which will turn some of the leaves yellow.
If you want to do more research on what pests could be living/damaging your trees, you should check out this article on 9 Different Animals And Insects That Live In Trees.
Sooty mold can only grow on honeydew, which is the waste left by aphids, scales, or other insects feeding on your Japanese blueberry tree or any plants near it. Bees or yellow jackets buzzing around your tree is a sign that there is a lot of honeydew on it.
You can get rid of some of the mold temporarily by spraying your tree’s leaves off with the garden hose. This doesn’t solve the pest problem that created the honeydew in the first place, so I recommend using neem oil, specifically Verdana USDA Organic Cold Pressed Neem Oil, to take them out and keep honeydew from continuing to form on the tree.
Leaf Rust Discoloring Leaves
The last common problem that Japanese blueberry trees experience is leaf rust. Leaf rust is caused by the fungus Naohidemyces vaccinii. Younger leaves are more vulnerable to this fungus and older leaves are more resistant. This fungus will grow faster in warmer weather, so it is more detrimental to Japanese blueberry trees in warmer climates.
According to Michigan State University, you will notice leaf rust by the yellow spots that grow on the leaves in mid-season that turn brownish-red as time goes on. The leaves will eventually fall off.
Luckily, the disease is not fatal to the tree. It is annoying, however, because it can ruin the beauty of your tree by causing leaf loss and stunting new bloom growth in the next spring.
The ailment can grow on your tree fast. The fungus can grow on leaves after 48 hours of wetness. Because of this, you should only water your Japanese blueberry tree at the soil line without getting any of the leaves wet. Avoid overwatering as well.
The first thing you should do if you notice leaf rust is to apply a fungicide to stop the spread and save the rest of your leaves. I suggest using Bonide 811 Copper 4E Fungicide on the leaves to keep any more from getting affected.
Rake up any fallen leaves beneath the tree and burn them (if your area allows it). Doing this will keep the fungus from being spread by humans, animals, air, or water.
Later on, in the season, some of the infected leaves will grow telia on it, which is a fungal structure that lets the fungus stay alive during the winter and reinfect again in the spring. That’s why it’s important to rake up the fallen leaves and destroy them.
Good maintenance of your Japanese blueberry tree will give it the best chance of flourishing into a gorgeous tree, shrub, or topiary, depending on your tastes. Its versatility and attractiveness make it a highly sought-after tree by those who have discovered it.
If you do decide to add this tree to your yard, make sure to give it the best chance of survival from the moment of planting. You can do this by choosing somewhere with good air circulation, full sun, and well-draining soil.
If you’re interested in growing other trees that can bear beautiful fruit, consider reading this blog on 6 Of The Best Fruit Trees That Have Shallow Roots.
If you have a Japanese blueberry tree, research to find out the best living conditions for it. Even though they are hardy plants, these trees are beautiful when they have flourished. Don’t waste your money with a sad blueberry tree when you could have a healthy and thriving one that compliments your yard!a
“Elaeocarpus Decipiens.” North Carolina Extension Gardener Plant Toolbox, NC State.
Koenig, Rich, and Mike Kuhns. “Control of Iron Chlorosis in Ornamental and Crop Plants.” Cooperative Extension, Utah State University, June 2010.
Schilder, Annemiek. “Beware of Blueberry Leaf Rust.” MSU Extension, Michigan State University, 20 Sept. 2018.