Plant disease & disorder profiles
Showing 26 of 74 profiles: symptoms, spread, host crops, and organic-first treatments.
Alternaria leaf spot
Alternaria brassicicola / A. spp.
A close cousin of early blight that specializes in brassicas and other crops, producing dark concentric-ringed spots that can turn a whole head black if left unmanaged.
- Hosts
- Cabbage, Broccoli, Cauliflower, Kale
Angular leaf spot
Pseudomonas syringae pv. lachrymans
A bacterium that produces angular, vein-bound spots on cucumber and melon leaves, often leaking a sticky ooze that dries into a white crust.
- Hosts
- Cucumber, Cantaloupe / Melon, Zucchini, Winter squash
Anthracnose
Colletotrichum spp.
A group of closely related fungi that cause sunken, water-soaked spots on ripening fruit and dark blotches on leaves and stems. Especially damaging on cucurbits, peppers, beans, and tomatoes right at harvest time.
- Hosts
- Cucumber, Winter squash, Pumpkin, Pepper
Apple scab
Venturia inaequalis
The most common apple disease in humid climates, producing olive-green, velvety spots on leaves and fruit that later turn dark and corky, sometimes cracking the fruit skin.
- Hosts
- Apple
Bacterial canker
Clavibacter michiganensis subsp. michiganensis
A systemic tomato bacterium that moves inside the plant's vascular system, causing one-sided wilting, stem cankers, and a telltale 'bird's-eye' spot on fruit.
- Hosts
- Tomato
Bacterial soft rot
Pectobacterium spp. (formerly Erwinia carotovora)
An opportunistic bacterium that enters through wounds, bruises, or insect damage and turns fleshy roots, bulbs, and stems into a soft, mushy, foul-smelling mass, often in storage.
- Hosts
- Potato, Carrot, Onion, Cabbage
Bacterial spot
Xanthomonas spp.
A seed- and splash-borne bacterium that riddles tomato and pepper leaves and fruit with small, scabby dark spots. Unlike fungal spots it has no rings and no fuzzy growth, just a greasy, water-soaked look at first.
- Hosts
- Tomato, Pepper
Bean rust
Uromyces appendiculatus
A fungus that produces powdery, rust-orange pustules on the underside of bean leaves, easily rubbed off on a finger like actual rust dust.
- Hosts
- Bush bean
Bitter rot
Colletotrichum spp.
A warm-weather anthracnose relative that causes sunken, circular brown rot spots on apple fruit, usually arranged in concentric rings of tan-orange spore pustules.
- Hosts
- Apple, Grape
Black rot (grape)
Guignardia bidwellii
A fungal disease specific to grapes that produces reddish-brown leaf spots and then completely mummifies developing berries into hard, black, wrinkled raisins.
- Hosts
- Grape
Blossom end rot
N/A — abiotic (calcium transport disorder)
A localized calcium deficiency at the fruit's blossom end, usually caused by inconsistent watering rather than a lack of calcium in the soil. Uneven moisture disrupts the plant's ability to move calcium into fast-growing fruit tissue.
- Hosts
- Tomato, Pepper, Zucchini, Winter squash
Brown rot
Monilinia fructicola
A fast-moving fungus that blights blossoms in spring and then rots ripening stone fruit into a soft brown mass covered in gray-tan powdery spore tufts, often spreading fruit to fruit where they touch.
- Hosts
- Peach, Plum, Cherry
Cedar-apple rust
Gymnosporangium juniperi-virginianae
A fungus with a bizarre two-host life cycle, spending part of its life on juniper/red-cedar trees (forming orange gelatinous 'horns' in spring) and part on apple and crabapple leaves and fruit.
- Hosts
- Apple
Cercospora leaf spot
Cercospora beticola (and related species)
A fungus that produces distinctive small circular spots with tan-gray centers and reddish-purple borders on beet, chard, and spinach leaves.
- Hosts
- Beet, Swiss Chard, Spinach
Common blight of beans
Xanthomonas axonopodis pv. phaseoli
A warm-weather bean bacterium producing large, irregular brown leaf blotches with a narrow yellow border, distinct from halo blight's cooler-weather, wide-halo look.
- Hosts
- Bush bean, Pole bean
Downy mildew (cucurbit)
Pseudoperonospora cubensis
A wind-dispersed water mold that produces angular, vein-bound yellow spots on the top of cucumber and melon leaves with a fuzzy gray-purple mold visible underneath.
- Hosts
- Cucumber, Cantaloupe / Melon, Watermelon, Zucchini
Early blight
Alternaria solani
A soil-dwelling fungus that starts on the oldest, lowest leaves and works upward. Classic sign is a brown spot with concentric rings, like a target, ringed by yellow tissue.
- Hosts
- Tomato, Potato, Eggplant
Gray mold (Botrytis blight)
Botrytis cinerea
An opportunistic fungus that colonizes dead or dying tissue (old flower petals, bruised fruit, wounds) and then spreads into healthy tissue, producing a fuzzy gray-brown mold coat.
- Hosts
- Tomato, Strawberry, Grape, Pepper
Gummy stem blight
Stagonosporopsis cucurbitacearum
A cucurbit-specific fungus causing leaf spots, stem cankers that ooze amber gum, and a fruit-rotting phase confusingly also called 'black rot' on melons and squash.
- Hosts
- Cucumber, Winter squash, Pumpkin, Watermelon
Halo blight
Pseudomonas savastanoi pv. phaseolicola
A bean-specific bacterium that produces small angular spots ringed by a wide, pale-green-to-yellow halo, often larger than the spot itself.
- Hosts
- Bush bean, Pole bean
Heat-induced blossom drop
N/A — abiotic (heat stress on pollen viability)
When nighttime temperatures stay too warm or daytime heat spikes too high, pollen becomes sterile or fails to release properly, so flowers form but abort and drop without setting fruit.
- Hosts
- Tomato, Pepper, Bush bean
Nitrogen deficiency
N/A — abiotic (nutrient deficiency)
Nitrogen is mobile within the plant, so when supply runs short, the plant pulls it from older leaves to support new growth, causing uniform yellowing that starts at the bottom of the plant.
- Hosts
- Corn, Cabbage, Tomato, Lettuce
Overwatering / root suffocation
N/A — abiotic (waterlogging, oxygen deprivation)
Saturated soil pushes air out of the pore spaces roots need to breathe, so roots suffocate and die even though the plant looks like it's drowning in symptoms that mimic drought.
- Hosts
- Tomato, Pepper, Cucumber, Bush bean
Potato virus Y
Potato virus Y (PVY)
An aphid-transmitted virus of potato (and related nightshades) that causes leaf mottling, mosaic patterns, and in some strains a distinctive necrotic ringspot on tubers.
- Hosts
- Potato, Pepper, Tomato
Septoria leaf spot
Septoria lycopersici
A relentless tomato-specific fungus that produces dozens of small, circular spots with tan centers and dark borders, each dotted with tiny black specks (the fungus's fruiting bodies).
- Hosts
- Tomato
Tomato spotted wilt virus
Tomato spotted wilt virus (TSWV)
A thrips-vectored virus with a very wide host range, causing bronzing, ring spots, and stunted, one-sided growth. Once thrips introduce it, there's no cure.
- Hosts
- Tomato, Pepper, Lettuce
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