Diseases
Compare the visible signs before you choose a diagnosis.
Plants get sick from fungi, bacteria and viruses. Start with what you see, check the pattern against the diseases below, then manage it. Few diseases can be cured once they are in a plant, so the work is slowing the spread and preventing the next one.
Start with what you see
Choose the symptom that looks most like your plant.
Fungal diseases
Fungi and water moulds thrive in damp, still air and spread quickly on wet leaves.
16 problems
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Powdery mildew
Zucchini, Pumpkins, Cucumbers A white, powdery coating on leaves that spreads in dry weather, weakening the plant. -
Downy mildew
Basil, Lettuce, Grapes Yellow, angular patches on top of leaves with grey-purple fuzz underneath. -
Early blight
Tomatoes, Potatoes Brown spots with target-like rings on the lower leaves of tomatoes and potatoes. -
Late blight
Tomatoes, Potatoes, Spinach Dark, water-soaked patches that spread fast in warm, wet weather, killing leaves, stems and fruit. -
Septoria leaf spot
Tomatoes, Parsley Many small round spots with pale centres and dark edges, starting on lower leaves. -
Fungal leaf spots
Beets, Broccoli, Cabbage Round brown or grey spots with darker rims on leaves, spreading in wet weather. -
Anthracnose
Cucumbers, Green beans, Avocado Sunken, dark spots on fruit and leaves, often with pink spore masses in wet weather. -
Grey mould (botrytis)
Strawberries, Raspberries, Grapes Fuzzy grey mould on fruit, flowers and damaged leaves, rotting them in cool, damp weather. -
Rust
Garlic, Onions, Mint Orange, brown or black powdery pustules on leaves, which yellow and fall. -
Damping off
Microgreens, Basil, Spinach Seedlings collapse at soil level with a thin, dark, pinched stem. -
Root rot
Aloe vera, Snake plant, Monstera Wilting and yellowing in wet soil; roots brown, soft and falling apart. -
Fusarium wilt
Tomatoes, Basil, Peas Leaves yellow and wilt, often on one side first; inside the stem is stained brown. -
Verticillium wilt
Strawberries, Tomatoes, Potatoes Lower leaves yellow and wilt, stems stained brown inside; strawberries and tomatoes collapse. -
Clubroot
Cabbage, Broccoli, Cauliflower Brassicas wilt on warm days and stay small; roots are swollen into knobbly clubs. -
Onion white rot
Onions, Garlic Onion and garlic leaves yellow and die; the bulb base is covered in white fluff and black specks. -
Sooty mould
Lemon trees, Aloe vera, Pineapple guava A black, sooty film on leaves that wipes off. It grows on honeydew from sap-sucking insects.
Bacterial diseases
Bacteria enter through wounds and pores and spread in splashing water, on hands and tools, and by insects.
4 problems
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Bacterial leaf spot
Bell peppers, Chili peppers, Tomatoes Small, dark, water-soaked spots on leaves and raised scabby spots on fruit, spreading in wet weather. -
Bacterial wilt
Cucumbers, Pumpkins, Zucchini Whole runners or plants wilt suddenly and die within days, without yellowing first. -
Bacterial soft rot and blackleg
Potatoes, Cabbage, Lettuce Stems black and slimy at the base, or tubers and heads rotting into foul-smelling mush. -
Aster yellows
Carrots, Lettuce Yellowed, twisted growth, bunched shoots and hairy, bitter roots; spread by leafhoppers.
Viral diseases
Viruses are carried by insects, seed, hands and tools. There is no cure: remove the plant, stop the carrier.
3 problems
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Cucumber mosaic virus
Cucumbers, Zucchini, Pumpkins Mottled yellow and green, puckered leaves, stunted plants and warty, mottled fruit. -
Tomato mosaic virus
Tomatoes, Bell peppers, Chili peppers Light and dark green mottling and fern-like leaves on tomatoes and peppers. -
Bean common mosaic virus
Green beans Light and dark green mosaic, puckered and cupped leaves, and stunted bean plants.
