Quick diagnosis for Japanese maple

When a Japanese maple shows marks on its foliage, the explanation is most often cultural (water, wind, sun, substrate) before it is a disease. The goal is to distinguish what is normal or temporary, what requires a simple adjustment, and what deserves closer attention.

The most reliable “reading” in four pointers

Pot or in the ground

In containers, symptoms are frequently linked to the substrate/watering duo (compaction, irregular watering, pot too small). In the ground, the dominant causes are often exposure and how the soil behaves in winter (too wet, poorly drained).

Overall or localized damage

A whole-tree issue points to general stress. A problem affecting one branch or one side deserves closer attention (wood / roots / sap flow).

A clear weather trigger

Dry wind, harsh sun, a very hot spell, a long wet period: recent weather context often explains the pattern of marks.

Time of season

Wet spring (leaf spots, powdery mildew), summer (leaf scorch, water stress), autumn (normal yellowing, often more pronounced after a difficult summer).

Common symptoms, likely causes, helpful actions

1) Brown edges, dry tips, “scorched” leaves

Most common reading: drying out (wind + sun) and/or irregular watering, especially in containers.
Prioritize :

• a more wind-sheltered position (often decisive),
• thorough waterings followed by a pause (avoid frequent small top-ups),
• checking drainage and the structure of the substrate.

These marks are often aesthetic: they do not necessarily indicate a disease.

2) Yellowing outside the autumn period

Two dominant cases.

Gradual overall yellowing

Often linked to root stress: compacted substrate, excess cold water, or repeated cycles of drying out. Prioritize: drainage, aeration, a more stable watering rhythm.

Yellowing between veins with greener veins (chlorosis)

Possible in container growing, especially with calcareous water/soil or an uptake imbalance. Prioritize: consistent culture, a structured substrate, avoiding excesses (fertilizer, overwatering).

3) Brown/black spots on leaves

Common reading : leaf spots encouraged by humidity (rainy spring).
Prioritize :

• collecting fallen leaves,
• avoiding watering the foliage,
• light aeration if the canopy is very dense.

In most cases, the impact is mainly visual if the plant is vigorous.

4) White powdery coating (“dusty” look)

Common reading : powdery mildew, often linked to insufficient air movement and certain temperature swings.
Prioritize :

• better air circulation,
• watering at the base, not on the leaves,
• removing heavily affected leaves if necessary.
  A treatment only makes sense if the attack becomes persistent.

5) Curled or misshapen leaves

Possible readings :

• stress (wind, sun, water “ups and downs”),
• pests (aphids), depending on visible presence.
  Prioritize : checking the underside of leaves, correcting conditions, avoiding excess nitrogen (overly tender foliage).
• Note: some cultivars naturally have curled/crinkled leaves (Okushimo, Shishigashira, Kuirui jishi, etc.).

6) Soft foliage in the afternoon, normal in the morning

Common reading : reaction to heat (transpiration), pot heating up, substrate drying quickly.

Prioritize :

• watering earlier in the morning during hot periods,
• light shading during the harshest hours,
• stabilizing the container (larger pot, insulating the pot, less exposed location).

When closer attention is useful

Asking for advice or running a diagnosis becomes relevant if:

• an entire branch dries out quickly,
• dieback appears on one side of the tree,
• decline is overall despite correct drainage,
• signs establish at the collar/trunk (wet black areas, oozing, progression).

FAQ

Why do the leaf edges turn brown?
Most often: drying wind, harsh sun and/or irregular watering (common in containers). It is not automatically a disease.

My Japanese maple turns yellow in summer — is it normal?
It’s not “expected”, but it is common in cases of root stress (excess cold water, compacted substrate, or repeated drought). Drainage and consistent culture are the first points to check.

Spots on leaves: a serious disease?
Often no. After a wet spring, leaf spotting can appear. Hygiene (fallen leaves) and better aeration are frequently enough.

White felt/powder on leaves: what is it?
Most often powdery mildew. Better air flow and watering at the base generally reduce pressure.

One branch is drying while the rest is fine — what does that mean?
A localized issue deserves more attention than a general symptom. Checking the wood and root conditions is recommended.