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Pest & Disease Atlas

What you'd see, what it might be instead, why it happens, and what actually works.

• Spider mitesTiny sap-suckers that stipple leaves pale and spin fine webbing in dry, warm rooms.
• MealybugsWhite cottony clusters tucked into leaf joints and along stems, leaving sticky honeydew behind.
• Scale insectsSmall brown or tan bumps glued to stems and leaf veins that do not move — until you look closely.
• ThripsSlender, fast insects that rasp leaves into silvery streaks and leave black specks behind.
• Fungus gnatsSmall dark flies drifting up from wet potting mix; the larvae in the soil are the real story.
• AphidsSoft pear-shaped insects clustered on tender new growth and flower buds, multiplying by the day.
• WhiteflyTiny white moth-like insects that rise in a cloud when leaves are brushed.
• SpringtailsTiny jumping specks in damp soil that alarm people but almost never harm a plant.
• Root rotRoots suffocate in waterlogged mix and are then colonised by water moulds; the plant wilts while the soil is wet.
• Powdery mildewA white, flour-like coating on leaf surfaces that wipes off, thriving in still air with humid nights.
• Leaf spot (fungal & bacterial)Round or angular spots, often with a yellow halo, spreading on leaves that stay wet.
• Grey mould (Botrytis)Fuzzy grey fur on flowers, soft stems and dead tissue in cool, damp, still air.
• White mould on soilA white fuzzy or crusty layer on the potting mix — usually a harmless mould telling you the surface stays damp.
• Edema (oedema)Corky, blister-like bumps on the undersides of leaves when roots take up water faster than leaves can lose it.
• Sunburn (leaf scorch)Bleached, papery patches on the leaves that face the window after a sudden increase in direct sun.
• Fertiliser & salt burnBrown crispy leaf tips and margins with a white crust on the soil or pot rim from accumulated salts.
• Nutrient deficienciesPatterned yellowing that tells you which nutrient the plant cannot get — often because of pH or roots, not because the soil is empty.
• Cold & draught damageSudden blackened, water-soaked or limp patches after a cold night, a draughty window or a chilly car ride home.
• Etiolation (stretching for light)Long pale stems, small leaves and wide gaps between them as the plant reaches for light it cannot find.
• Low humidityCrisp brown edges, curling leaves and buds that drop when the air is drier than the plant evolved for.
• Underwatering & hydrophobic soilA light pot, crisp or drooping leaves, and water that runs straight down the sides without soaking in.

Sensei never gives a definitive diagnosis from a description alone. Use the Atlas to narrow it down, then confirm by watching the next leaf.