Japanese blueberry is a tough, popular evergreen for hedges and screens in warm regions, and it rarely gets serious disease. It often looks worse than it is, because a few of its warning signs are part of its normal life. Most problems trace back to soil, water, weather, pests, or how the tree was planted, and these can usually be fixed if caught early.1Verdant Tree Farm. Japanese Blueberry Tree: The Ultimate Houston Privacy & Specimen Guide
Red Leaves Dropping Is Often Normal
Japanese blueberry regularly sheds old leaves, and they turn bright red or yellow before they drop.2National Gardening Association. Newly planted Japanese blueberry trees shedding old leaves while pushing new growth This happens every spring, and again while a newly planted tree settles in.3National Gardening Association. Newly planted Japanese blueberry trees shedding old leaves while pushing new growth
What matters is whether fresh growth is coming in. A healthy tree drops old leaves while pushing out new ones.4National Gardening Association. Newly planted Japanese blueberry trees shedding old leaves while pushing new growth Leaves falling with no new growth, and branches dying back from the tips, signal real trouble.5National Gardening Association. Newly planted Japanese blueberry trees shedding old leaves while pushing new growth
The check takes about five minutes. Look at the branch ends for soft, light-green new shoots. Then scratch a twig with a fingernail: green underneath means it is alive, while brown and dry means it is dead. Also notice which leaves are falling. Healthy shedding is mostly older leaves toward the inside of the plant, not the new ones at the outer edges.
People often add fertilizer or extra water to a tree that is shedding normally. The extra water can create the soggy soil that leads to root rot, covered below. If new growth is present, the best treatment is patience and steady care. If leaves keep dropping into summer with no new growth, look at the causes in the sections below.
Yellow Leaves From Alkaline Soil
Japanese blueberry is prone to yellowing caused when the tree cannot get enough iron.672 Tree. Japanese Blueberry Tree Problems and Solutions Plants need iron to make the green pigment that powers growth.772 Tree. Japanese Blueberry Tree Problems and Solutions Yellow leaves eventually fall, and bare branches can start to die.872 Tree. Japanese Blueberry Tree Problems and Solutions
Iron yellowing looks different from the normal red shedding. It usually starts in newer leaves, and the veins stay green while the rest of the leaf turns yellow.
The soil itself seldom lacks iron. More often the pH keeps the roots from absorbing it.972 Tree. Japanese Blueberry Tree Problems and Solutions The tree does best at a soil pH of about 6.1 to 7.5.1072 Tree. Japanese Blueberry Tree Problems and Solutions Alkaline soil above that range locks up iron, which is common in limey Southwestern clay.
To find out where you stand, use a home kit or send a soil test to your county extension office. Elemental sulfur lowers pH slowly, over months, and should go on at the label rate. Acid-forming fertilizers help keep pH lower over time. Avoid planting near concrete foundations or driveways, which can raise pH.
For quicker greening, chelated iron applied to the soil or sprayed on the leaves can green the tree within weeks. That is only a short-term fix if the pH stays high, so combine the iron with pH correction for a lasting result.
Brown Edges From Heat and Watering
Leaf scorch shows up as browning or shriveling along leaf edges, sometimes spreading along the veins.11arborday.org. Scorch and Stress: Reading Your Tree’s Summer Signals It happens when a tree loses water faster than it can replace it.12arborday.org. Scorch and Stress: Reading Your Tree’s Summer Signals Heat, drought, and uneven watering are the usual triggers.13arborday.org. Scorch and Stress: Reading Your Tree’s Summer Signals
Water deeply and less often rather than giving light daily sprinkles. Newly planted trees need regular water through their first summer. Spread mulch 2 to 3 inches deep, keeping it away from the trunk, to hold moisture. Before watering, push a finger a few inches into the soil to check that it is dry.
Scorch that appears in wet soil may mean damaged roots rather than too little water. Rotted or circling roots cannot move water to the leaves either. If more watering does not help, check the roots, as described in the sections below.
Browned leaf edges will not turn green again. Fix the watering, then judge progress by the new leaves.
Black Sooty Mold and Scale Insects
Black sooty mold on Japanese blueberry usually points to scale, a sap-sucking insect.14Ask Extension. black sooty mold japanese blueberry trees Scale excretes honeydew, sticky droppings that the mold grows on.15Ask Extension. black sooty mold japanese blueberry trees Different scale species attack leaves or bark.16Ask Extension. black sooty mold japanese blueberry trees To look for the insects, scrape the bark under the mold with a pocket knife.17Ask Extension. black sooty mold japanese blueberry trees
Scale looks like small bumps, flat or rounded, stuck to stems or the undersides of leaves. They often look like part of the bark rather than like bugs. If you crush a live one it may ooze liquid, while dead scale is usually dry and may flake off.
Horticultural oil sprays, which are light oils made for use on plants, control scale well.18LSU AgCenter. Black Moldy Substance The oil coats and suffocates the insects, so every branch and leaf surface must be covered.19LSU AgCenter. Black Moldy Substance Two or three applications in a row, following the label, are usually needed.20LSU AgCenter. Black Moldy Substance The mold does not vanish right away; it weathers off over time.21LSU AgCenter. Black Moldy Substance
Avoid spraying oil in heat above about 90°F or in strong sun, which can burn leaves. Water the tree beforehand if it is dry. Also check for ants climbing the trunk, since they protect scale from predators.
Curled New Leaves From Thrips
Thrips feed at the tips of new shoots and leaves.22UC IPM. Blueberry Citrus Thrips Management New leaves curl and discolor, and shoots can be stunted or scarred.23UC IPM. Blueberry Citrus Thrips Management Thrips can also bronze young leaves along the veins and cause the tips to die back.24UF/IFAS Extension Suwannee County. Topic Tuesday: Chilli Thrips Heavy outbreaks during long hot, dry spells can cause widespread curling and leaf drop.25UF/IFAS Extension Suwannee County. Topic Tuesday: Chilli Thrips
To confirm them, tap a new shoot over white paper and look for tiny moving slivers. The damage appears on the newest leaves while older leaves look fine, which separates it from scorch, where the edges of older leaves brown.
Older foliage often grows back once the weather cools. Spinosad or insecticidal soap aimed at the new growth can help. Avoid heavy nitrogen feeding, which produces the soft shoots thrips favor, and keep the tree well watered during dry spells.
Speckled Leaves From Spider Mites
Spider mites pierce leaf cells and suck out the contents, leaving pale dots.26University of Kentucky College of Agriculture. Spider Mites on Landscape Plants Leaves look stippled and can turn bronze.27UC Statewide IPM Program. Spider Mites / Home and Landscape / UC Statewide IPM Program Mites thrive in hot, dry, dusty conditions, often near roads or along the edges of a yard.28UC Statewide IPM Program. Spider Mites / Home and Landscape / UC Statewide IPM Program A new generation can develop in under a week, so numbers peak from June through September.29UC Statewide IPM Program. Spider Mites / Home and Landscape / UC Statewide IPM Program
To check, hold white paper under a branch and tap it; specks that move are mites. Fine webbing may appear on the undersides of leaves, and a hand lens makes the tiny mites easier to see.
Hose the foliage regularly to knock mites off and wash away dust. Horticultural oil or insecticidal soap works if it reaches the undersides of leaves. Broad-spectrum insecticides can make mites worse by killing their natural predators.
Root Rot in Wet Heavy Soil
In soggy soil, root rot organisms release swimming spores.30Pacific Northwest Pest Management Handbooks. Blueberry (Vaccinium corymbosum)-Root Rot The spores reach the fine feeder roots and kill them.31Pacific Northwest Pest Management Handbooks. Blueberry (Vaccinium corymbosum)-Root Rot That is why root rot is far worse in heavy, poorly drained soil.32Pacific Northwest Pest Management Handbooks. Blueberry (Vaccinium corymbosum)-Root Rot
The signs are wilting or yellowing despite moist soil, and roots that are brown and mushy instead of firm and pale. Leaf drop with no new growth fits too.
Cut back watering and let the top few inches of soil dry out. For new plantings in clay, plant slightly high or on a berm. Do not pile soil or mulch against the trunk. A badly rotted tree may not recover, so prevention matters most.
Slow Decline From Circling Roots
Girdling roots often form in root-bound container plants and can start at transplanting.33University of Maryland Extension. What is a girdling root? As they thicken, they wrap tighter around the trunk base.34HortGuide. Circling Roots: What Happens When You Plant a Pot-Bound Tree They cut off the flow of water and nutrients.35HortGuide. Circling Roots: What Happens When You Plant a Pot-Bound Tree A root as thin as a pencil is minor, but one as thick as a thumb is a real threat.36HortGuide. Circling Roots: What Happens When You Plant a Pot-Bound Tree
Affected trees usually decline over 5 to 10 years.37University of Maryland Extension. What is a girdling root? One side of the crown often thins first, and the tree can lean or fail.38HortGuide. Circling Roots: What Happens When You Plant a Pot-Bound Tree
At planting, slide the tree out of the pot and look for roots circling the outside of the root ball. Tease out or cut through circling roots before planting, and make sure the root flare, where the trunk widens, sits at soil level.
For an established tree, gently pull soil away from the trunk base to look for roots crossing it. A trunk that goes straight into the ground with no flare is a warning sign. An arborist can remove large circling roots safely.
Freeze Damage and Cold Protection
The tree is fairly cold-hardy.39Ask Extension. Japanese Blueberry freeze damage? Still, one Gulf Coast grower treats 20°F as the point to take action.40Verdant Tree Farm. Japanese Blueberry Tree: The Ultimate Houston Privacy & Specimen Guide Before a hard freeze, spread 4 inches of mulch over the roots and cover the tree with breathable frost cloth, not plastic.41Verdant Tree Farm. Japanese Blueberry Tree: The Ultimate Houston Privacy & Specimen Guide Plastic traps moisture and can cause more damage.42Verdant Tree Farm. Japanese Blueberry Tree: The Ultimate Houston Privacy & Specimen Guide
Drape the cloth all the way to the ground to trap heat rising from the soil, and remove it when temperatures climb above freezing. Water the soil before a freeze, because moist soil holds heat better than dry soil.
After a freeze, dry brown leaves and branches can stay on to insulate the tree against another freeze.43Ask Extension. Japanese Blueberry freeze damage? So wait until about March to prune.44Verdant Tree Farm. Japanese Blueberry Tree: The Ultimate Houston Privacy & Specimen Guide Cut back branches that turn mushy right away to prevent rot.45Ask Extension. Japanese Blueberry freeze damage?
When spring comes, scratch the twigs and look for green tissue. Wait to see where new buds break before cutting, then prune back to live wood just above a healthy bud.
Preventing Problems at Planting
Spacing trees properly at planting improves airflow, which is especially important in humid climates.46Verdant Tree Farm. Japanese Blueberry Tree: The Ultimate Houston Privacy & Specimen Guide Loosen compacted soil across a wide area before planting.47Arboriculture & Urban Forestry. Soil Compaction Effects on the Establishment of Three Tropical Tree Species
Japanese blueberry grows large, so follow the mature width listed on the plant tag. Leave room between a hedge and walls so air can move.
Diseases can spread through cuttings taken from infected plants.48smallfruits.org. Blueberry Propagation Suggestions Buy from a reputable nursery and inspect plants for cankers, scale, and circling roots. Look for even, glossy green leaves without black film. Avoid trees with thick roots poking out of the pot, and check stems for swellings or sunken patches.