Plant Clinic · Category

Fungal & Bacterial Disease

Powdery mildew, leaf spot, botrytis, sooty mould, and other fungal infections.

101 problems42 Moderate40 Critical19 Minor

Fungal and bacterial diseases thrive in conditions of high humidity, poor air circulation, and overhead watering. They can spread rapidly through a plant collection once established. Early identification — based on the specific pattern of lesions, colour, texture, and location — is critical for effective treatment before the pathogen spreads.

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All Fungal & Bacterial Disease

Powdery Mildew — Erysiphe & Golovinomyces spp. — anthurium plant care

⚠ Moderate

Begonia rex

Powdery Mildew — Erysiphe & Golovinomyces spp.

A white to grey powdery coating appears on leaf surfaces, stems, and occasionally flower buds. Unlike other fungal diseases, powdery mildew grows on the surface rather than inside plant tissue, giving it a dusted-flour appearance. Affected tissue may yellow beneath the coating. Unlike downy mildew, it occurs on the upper leaf surface and does not require standing water — in fact, it thrives in dry conditions with high humidity.

Bacterial & Fungal Leaf Spot — Xanthomonas & Cercospora spp. — calathea plant care

⚠ Moderate

Ficus lyrata (Fiddle Leaf Fig)

Bacterial & Fungal Leaf Spot — Xanthomonas & Cercospora spp.

Dark brown to black spots with yellow halos appear on leaf surfaces, often water-soaked in early stages. Bacterial spots have irregular margins and a translucent, greasy appearance when held to light. Fungal spots (Cercospora, Alternaria) develop concentric rings with a tan, dry centre. Spots coalesce under humid conditions to form large necrotic patches.

Anthracnose — Colletotrichum Leaf Blight — monstera plant care

⚠ Moderate

Anthurium andraeanum

Anthracnose — Colletotrichum Leaf Blight

Dark brown to black sunken lesions develop on leaves, often beginning at the tip or margin and expanding inward in irregular patches. Under humid conditions, tiny salmon-pink to orange spore masses may be visible within the lesions. Affected tissue dries and turns papery, and severe infections can blight entire leaves and spread to petioles.

Fusarium Wilt — Vascular Browning & Collapse — monstera plant care

⚠ Critical

Syngonium podophyllum

Fusarium Wilt — Vascular Browning & Collapse

Lower leaves yellow and wilt progressively, often on one side of the plant first, despite adequate soil moisture. The wilting is permanent and advances upward as the fungus colonises the vascular system. A diagnostic sign is brown to reddish streaking inside the stem when sliced open lengthwise, marking the blocked water-conducting tissue.

⚠ Critical

Philodendron spp.

Southern Blight — Sclerotium rolfsii

The plant collapses rapidly as the stem rots at and just above the soil line. A diagnostic white, fan-like fungal mat (mycelium) appears on the lower stem and surrounding substrate, studded with small round structures resembling mustard seeds — the sclerotia — which start white and mature to tan-brown. Wilting is sudden and the lower stem turns soft and brown.

Rhizoctonia Damping-Off in Seedlings & Cuttings — anthurium plant care

⚠ Critical

Aroid seedlings & cuttings — Philodendron

Rhizoctonia Damping-Off in Seedlings & Cuttings

Young seedlings and freshly potted cuttings collapse suddenly, with a dark, water-soaked, pinched lesion girdling the stem at the soil line. The tissue above the constriction topples over while still green, and fine brown fungal threads may be visible on the stem base or substrate. Germinating seeds may rot before emerging.

Botrytis Grey Mould on Soft Tissue — philodendron plant care

⚠ Moderate

Begonia

Botrytis Grey Mould on Soft Tissue

A fuzzy grey-brown mould develops on soft, damaged, or senescing tissue — wilting flowers, wounded leaves, and decaying lower foliage. Affected tissue first becomes water-soaked and brown, then is rapidly covered in the characteristic dusty grey sporulation. Spores release in visible clouds when disturbed and spread readily in cool, humid, still air.

Leaf Rust — Pustules on Undersides — philodendron plant care

⚠ Moderate

Anthurium spp.

Leaf Rust — Pustules on Undersides

Small raised pustules — yellow, orange, brown, or rust-red — erupt on the undersides of leaves, with corresponding yellow flecks visible on the upper surface. As pustules rupture they release powdery spores that smudge onto a finger. Heavy infections cause yellowing, premature leaf drop, and a generally weakened, unsightly plant.

Bacterial Blight — Xanthomonas on Anthurium — philodendron plant care

⚠ Critical

Anthurium andraeanum

Bacterial Blight — Xanthomonas on Anthurium

Water-soaked, translucent lesions appear at leaf margins and hydathodes, often surrounded by a bright yellow halo, and spread inward along veins. In systemic infection, the bacteria enter the vascular system, causing bronzing, wilting, and a dull, yellowed, declining plant. Lesions have a greasy, wet appearance when backlit and may ooze under high humidity.

Bacterial Wilt — Ralstonia & Erwinia Vascular Infection — philodendron plant care

⚠ Critical

Anthurium andraeanum

Bacterial Wilt — Ralstonia & Erwinia Vascular Infection

The plant wilts suddenly and completely despite adequate soil moisture and no root rot symptoms. Wilting may affect individual branches or the entire plant simultaneously. If a wilted stem is cut transversely, the vascular tissue (xylem bundles) appears brown or discoloured rather than white. In Ralstonia infections, a milky bacterial ooze may exude from cut stems when squeezed. The plant does not recover after watering — vascular damage is irreversible once systemic infection is established.

Humidity Tray Mould — Stagnant Water Breeding Fungus Gnats & Mould — peace-lily plant care

⚠ Minor

Most aroids in moist or terrarium conditions — Calathea

Humidity Tray Mould — Stagnant Water Breeding Fungus Gnats & Mould

White or grey mould grows on the pebbles or water surface of a humidity tray placed beneath the plant. Fungus gnat populations increase near the plant. A musty smell develops. While humidity trays can be effective tools for raising local RH, the standing water becomes a breeding site for fungus gnats (Bradysia spp.) and supports the growth of various moulds that can spread to the substrate surface and cause soil-level issues.

Red rust spots on snake plant from Fusarium fungal infection — Sansevieria treatment

⚠ Moderate

Sansevieria trifasciata / Dracaena trifasciata (Snake Plant)

Snake Plant Red & Rust Spots — Fusarium Fungal Leaf Spot

Small, reddish-brown to rust-coloured circular or oval spots appear scattered across the leaf surface, sometimes with a yellow halo. The spots are dry and slightly sunken. In humid conditions, spots may enlarge and develop a light-coloured centre. This is Fusarium fungal leaf spot — one of the few foliar pathogens that affects Sansevieria. It is opportunistic, typically colonising leaves that have been physically damaged (scratches, tip damage) or that have been kept wet from overhead watering.

Powdery Mildew on Chili Pepper Leaves � chili pepper plant care

⚠ Moderate

Capsicum annuum

Powdery Mildew on Chili Pepper Leaves

A white to grey powdery coating appears on the upper surface of leaves, starting as small circular patches that expand and merge. Affected leaves may yellow and drop prematurely, weakening the overall plant.

Bacterial Leaf Spot on Pepper Plants � chili pepper plant care

⚠ Moderate

Capsicum annuum

Bacterial Leaf Spot on Pepper Plants

Small, dark, water-soaked spots appear on leaves, often with a yellow halo around each lesion. Spots may merge into larger dead patches, and severely affected leaves yellow and drop. Fruit can also develop raised, scab-like spots.

Powdery Mildew on Mint Leaves � mint plant care

⚠ Moderate

Mentha spicata

Powdery Mildew on Mint Leaves

A white, powdery coating develops on the upper surface of leaves, usually starting on older growth low in the patch. Affected leaves may curl slightly and eventually yellow and dry out.

Mint Rust � Orange Pustules on Leaves and Stems � mint plant care

⚠ Critical

Mentha spicata

Mint Rust � Orange Pustules on Leaves and Stems

Small, bright orange, powdery pustules appear on the underside of leaves and along stems, typically emerging in spring from overwintering rhizomes. Severely affected shoots become distorted, and heavily infected plants can defoliate.

⚠ Minor

Mentha spicata

Leaf Spot on Mint

Small, circular brown or tan spots appear scattered across leaves, sometimes with a darker border. Spots may merge in severe cases, causing affected leaves to yellow and drop prematurely.

Downy Mildew on Basil � basil plant care

⚠ Critical

Ocimum basilicum (Basil)

Downy Mildew on Basil

Yellow, angular patches appear on the upper surface of leaves, following the leaf veins, while a fuzzy grey-purple mould develops on the underside directly beneath the yellowed area. Affected leaves eventually turn brown and collapse.

Fusarium Wilt on Basil � basil plant care

⚠ Critical

Ocimum basilicum (Basil)

Fusarium Wilt on Basil

One side of the plant wilts and yellows while the other side may still look healthy, often with dark streaking visible inside the stem when cut open. Affected plants decline steadily and rarely recover once symptoms are advanced.

Bacterial Leaf Spot on Basil � basil plant care

⚠ Moderate

Ocimum basilicum (Basil)

Bacterial Leaf Spot on Basil

Small, dark, water-soaked spots appear on leaves, sometimes with a yellow halo, and may merge into larger irregular dead patches in humid conditions. Affected leaves can look tattered as tissue within the spots dries and falls away.

Early Blight on Tomato Leaves � tomato plant care

⚠ Moderate

Solanum lycopersicum (Tomato)

Early Blight on Tomato Leaves

Dark brown spots with concentric rings, resembling a target or bullseye, appear on older, lower leaves first. A yellow halo often surrounds each spot, and severely affected leaves yellow entirely and drop.

Late Blight on Tomato Plants � tomato plant care

⚠ Critical

Solanum lycopersicum (Tomato)

Late Blight on Tomato Plants

Large, irregular, water-soaked grey-green patches spread rapidly across leaves, often with a white fuzzy mould visible on the underside in humid conditions. Stems can develop dark lesions, and fruit shows firm, brown, irregular blotches. The disease can destroy an entire plant within days.

Septoria Leaf Spot on Tomatoes � tomato plant care

⚠ Moderate

Solanum lycopersicum (Tomato)

Septoria Leaf Spot on Tomatoes

Numerous small, circular spots with dark brown borders and pale grey centres appear across lower leaves first, each spot often containing tiny black specks (fungal fruiting bodies) visible on close inspection. Heavily affected leaves yellow and drop.

Powdery Mildew on Rosemary � rosemary plant care

⚠ Minor

Salvia rosmarinus (Rosemary)

Powdery Mildew on Rosemary

A white, powdery coating develops on stems and needle-like leaves, usually in humid, still conditions. Affected growth can look dusty grey-white and may weaken over time.

Grey Mould (Botrytis) on Rosemary � rosemary plant care

⚠ Moderate

Salvia rosmarinus (Rosemary)

Grey Mould (Botrytis) on Rosemary

A fuzzy grey-brown mould develops on stems and foliage, usually starting on damaged, dying, or densely packed growth. Affected sections soften and can collapse if the infection spreads.

Fusarium Wilt on Tomato Plants — tomato plant care

⚠ Critical

Solanum lycopersicum (Tomato)

Fusarium Wilt on Tomato Plants

Lower leaves yellow on one side of the plant first, then wilt during the heat of the day and partially recover overnight, before the whole plant declines. Cutting the stem reveals brown discolouration in the vascular tissue.

Verticillium Wilt on Tomato Plants — tomato plant care

⚠ Critical

Solanum lycopersicum (Tomato)

Verticillium Wilt on Tomato Plants

V-shaped yellow lesions form on lower leaf margins, spreading inward, while the plant wilts gradually over weeks rather than collapsing suddenly. Vascular tissue shows a lighter tan-brown streaking than Fusarium wilt, and symptoms appear in cooler weather.

Bacterial Canker on Tomato — tomato plant care

⚠ Critical

Solanum lycopersicum (Tomato)

Bacterial Canker on Tomato

Leaf margins brown and curl upward starting from the bottom of the plant, often on just one side of a leaf or stem. Stems may develop dark streaks or open cankers, and fruit can show small white-haloed 'bird's-eye' spots.

Leaf Mold on Tomato Plants — tomato plant care

⚠ Moderate

Solanum lycopersicum (Tomato)

Leaf Mold on Tomato Plants

Pale yellow patches appear on the upper leaf surface, with an olive-green to grey-brown velvety mould growing directly beneath them on the underside. Common in greenhouse and high-tunnel tomatoes with limited airflow.

Powdery Mildew on Tomato Leaves — tomato plant care

⚠ Moderate

Solanum lycopersicum (Tomato)

Powdery Mildew on Tomato Leaves

A white to grey powdery coating spreads across the upper leaf surface, typically starting on older leaves. Unlike tomato-specific leaf mold, this coating is dry and dusty, not velvety, and can occur even in relatively dry conditions.

⚠ Moderate

Cucurbita pepo

Powdery Mildew on Pumpkin Leaves

A white powdery coating spreads across leaf surfaces and stems, starting as small circular patches that merge into larger areas. Heavily affected leaves yellow, dry out, and die back, reducing the plant's ability to size up fruit.

⚠ Critical

Cucurbita pepo

Downy Mildew on Pumpkin

Yellow, angular patches bounded by leaf veins appear on the upper leaf surface, with a grey-purple fuzzy growth on the underside directly beneath. Unlike powdery mildew, lesions are angular rather than circular and follow the leaf's vein pattern.

⚠ Critical

Cucurbita pepo

Bacterial Wilt on Pumpkin Vines

Individual leaves wilt during the day and may partially recover at night at first, but the whole vine collapses within days as the disease progresses. Cutting a wilted stem and pressing the cut ends together produces a sticky, stringy bacterial ooze when slowly pulled apart.

⚠ Moderate

Cucurbita pepo

Fruit Rot on Developing Pumpkins

A soft, water-soaked spot develops on the fruit, usually where it contacts damp soil, and expands rapidly into a mushy, collapsing area, sometimes with visible white or grey mould growth.

⚠ Moderate

Cucurbita pepo

Anthracnose on Pumpkin Leaves and Fruit

Small yellow-brown spots appear on leaves, expanding into larger dead patches that can cause leaves to tear and shred in wind. On fruit, sunken, dark, circular lesions develop, sometimes with a pink-orange spore mass visible in humid conditions.

⚠ Critical

Passiflora edulis (Passion Fruit)

Fusarium Wilt on Passion Fruit Vines

The vine wilts progressively from the tips inward, with leaves yellowing and dropping even though soil moisture seems adequate. Cutting the stem reveals brown vascular streaking.

⚠ Moderate

Passiflora edulis (Passion Fruit)

Brown Spot on Passion Fruit Leaves

Circular brown spots with concentric rings appear on leaves and can spread to stems and fruit, causing premature leaf drop and sunken fruit lesions.

⚠ Moderate

Passiflora edulis (Passion Fruit)

Septoria Spot on Passion Fruit

Small, angular, grey-brown spots with darker borders scatter across leaves, eventually causing widespread yellowing and leaf drop in humid conditions.

⚠ Moderate

Passiflora edulis (Passion Fruit)

Powdery Mildew on Passion Fruit

A white powdery coating develops on leaf surfaces, usually in humid conditions with poor airflow, weakening affected leaves over time.

⚠ Critical

Musa acuminata

Panama Disease (Fusarium Wilt) on Banana

Older leaves yellow at the edges and progressively collapse, hanging down around the pseudostem like a skirt, while the plant's growth stalls. Cutting the pseudostem reveals reddish-brown vascular discolouration.

⚠ Critical

Musa acuminata

Black Sigatoka Leaf Spot on Banana

Small brown-black streaks appear on leaves, expanding into larger dead patches with yellow halos, eventually causing widespread leaf death and reduced fruit yield.

⚠ Minor

Musa acuminata

Powdery Mildew on Banana Leaves

A white powdery coating occasionally develops on leaf surfaces in humid, still conditions with poor airflow, though this is less common than on many other plants.

⚠ Critical

Actinidia deliciosa

Bacterial Canker (Psa) on Kiwi Vines

Reddish-brown, angular leaf spots with yellow halos appear, along with cane cankers that ooze a rust-red bacterial exudate, and entire canes or the whole vine can collapse in severe cases.

⚠ Moderate

Actinidia deliciosa

Botrytis Grey Mould on Kiwi Fruit

A fuzzy grey mould develops on fruit, often starting at the stem end, spreading rapidly especially on fruit in storage or during cool, humid weather near harvest.

⚠ Moderate

Actinidia deliciosa

Powdery Mildew on Kiwi Leaves

A white powdery coating develops on leaf surfaces, particularly in humid conditions with poor airflow through a dense canopy.

⚠ Minor

Actinidia deliciosa

Leaf Spot on Kiwi Vines

Small, circular brown spots scatter across leaves, sometimes merging into larger dead patches in humid conditions, causing premature leaf drop.

⚠ Moderate

Vitis vinifera

Powdery Mildew on Grape Vines

A white to grey powdery coating spreads across leaves, shoots, and berries, causing distorted growth and cracked, scarred fruit skin in severe cases.

⚠ Critical

Vitis vinifera

Downy Mildew on Grape Vines

Yellow, oily-looking patches appear on the upper leaf surface, with a white-grey downy growth on the underside directly beneath. Infected berries can shrivel and turn leathery brown.

⚠ Critical

Vitis vinifera

Black Rot on Grape Vines

Small tan spots with dark borders appear on leaves, while infected berries shrivel into hard, black, mummified fruit that often remains attached to the cluster.

⚠ Critical

Vitis vinifera

Botrytis Bunch Rot on Grapes

A fuzzy grey mould develops on ripening berries, spreading rapidly through tightly-packed clusters, especially after rain near harvest time.

⚠ Moderate

Vitis vinifera

Anthracnose on Grape Vines

Small circular spots with dark borders and pale grey centres appear on leaves, shoots, and berries, sometimes creating a 'bird's eye' pattern on fruit.

⚠ Moderate

Cucumis sativus (Cucumber)

Powdery Mildew on Cucumber Leaves

A white powdery coating spreads across leaf surfaces, starting on older leaves and expanding rapidly, weakening the plant and reducing fruit quality.

⚠ Critical

Cucumis sativus (Cucumber)

Downy Mildew on Cucumber Leaves

Angular yellow patches bounded by leaf veins appear on the upper surface, with grey-purple fuzzy growth on the underside, spreading rapidly in humid weather.

⚠ Critical

Cucumis sativus (Cucumber)

Bacterial Wilt on Cucumber Vines

Individual leaves wilt during the day, then the whole vine collapses within days. Cutting a wilted stem and slowly pulling the cut ends apart produces a sticky, stringy bacterial ooze.

⚠ Moderate

Cucumis sativus (Cucumber)

Angular Leaf Spot on Cucumber

Small, angular, water-soaked spots bounded by leaf veins appear on foliage, sometimes with a milky bacterial ooze visible on the underside in humid conditions.

⚠ Moderate

Cucumis sativus (Cucumber)

Fruit Rot on Cucumbers

A soft, water-soaked spot develops on fruit, usually where it contacts damp soil, expanding rapidly into a mushy, collapsing area.

⚠ Moderate

Cucumis sativus (Cucumber)

Anthracnose on Cucumber Plants

Dark, sunken, circular spots develop on leaves, stems, and fruit, sometimes with a pinkish spore mass visible on fruit lesions in humid conditions.

⚠ Critical

Brassica oleracea var. italica (Broccoli)

Clubroot on Broccoli

The plant wilts in the heat of the day and looks stunted and pale, with roots showing swollen, distorted, club-like galls when dug up.

⚠ Critical

Brassica oleracea var. italica (Broccoli)

Black Rot on Broccoli

V-shaped yellow lesions form at leaf margins, with blackened veins visible within the yellowed tissue, eventually causing the whole leaf to die.

⚠ Moderate

Brassica oleracea var. italica (Broccoli)

Downy Mildew on Broccoli

Pale yellow patches appear on the upper leaf surface, with a white-grey downy growth on the underside directly beneath, most common on young seedlings.

⚠ Minor

Brassica oleracea var. italica (Broccoli)

Powdery Mildew on Broccoli

A white powdery coating develops on leaf surfaces, typically later in the season during warm, dry weather with cool nights.

⚠ Minor

Brassica oleracea var. italica (Broccoli)

White Rust on Broccoli

White, blister-like pustules form on the underside of leaves, with corresponding yellow patches on the upper surface, and severely affected leaves distort.

⚠ Minor

Carica papaya (Papaya)

Powdery Mildew on Papaya Leaves

A white powdery coating develops on leaf surfaces, typically in humid conditions, weakening affected leaves and reducing overall vigour.

⚠ Moderate

Carica papaya (Papaya)

Anthracnose Fruit Rot on Papaya

Small, water-soaked spots appear on ripening fruit, expanding into sunken, dark lesions, often with a pink-orange spore mass visible in humid conditions.

⚠ Minor

Carica papaya (Papaya)

Black Spot (Cercospora) on Papaya Leaves

Small, angular, dark brown to black spots scatter across leaves, sometimes merging into larger dead patches and causing premature leaf drop.

⚠ Critical

Carica papaya (Papaya)

Bacterial Crown Rot on Papaya

The growing point (crown) at the top of the tree turns soft, water-soaked, and foul-smelling, and can cause the entire top of the tree to collapse.

⚠ Critical