Check these first
- What shape is the damage: round holes, only veins left, white trails, or a pale stippling?
- Where are the insects or droppings: under the leaves, on new shoots, or at the base?
- If nothing is visible by day, check at night or early morning for cutworms and slugs.
Most likely causes
From the pests and diseases recorded for this plant, the ones whose symptoms match, most serious first. Symptoms alone rarely confirm a cause, so use the linked page to check the signs and treatment.
Aphids
Small green or black insects cluster on shoot tips and leaf undersides, crinkling the leaves and stopping growth. The honeydew they excrete supports sooty mold that blackens the foliage.
How to identify and treat: AphidsNettle Caterpillars
From summer into autumn they cluster on leaf undersides and graze the tissue so the leaves turn translucent white. Larger larvae riddle the leaves with holes and strip the branches bare.
How to identify and treat: Nettle CaterpillarsLonghorn Beetles
Sawdust-like frass is pushed out at the trunk base or branch crotches. The wood is hollowed out, the tree loses vigor, and the trunk may snap in strong wind.
How to identify and treat: Longhorn BeetlesOther possible causes
The three above are the causes on record for this symptom.
What other growers did about it
A page like this one can tell you what japanese maple pests and bug damage is and what to try. What it cannot tell you is what actually happened to someone who had it on the same plant, at the same point in the season, and what they did next.
Gadenin is a free garden journal built around that. You photograph the plant, tag what you are seeing, and the entries line up by date for each plant you grow.
- Tag the problem and the app tells you how many other growers have logged the same thing on the same plant.
- Growers who make their records public can be followed, so you can read what they did and how it turned out.
- Next season your own entries come back at the same point in the year, so you check the plant before it starts.
Free on iPhone. Recording, tagging and reading public records cost nothing.