Plant disease & disorder profiles
Showing 30 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
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
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
Black rot of brassicas
Xanthomonas campestris pv. campestris
A vascular bacterium of cabbage-family crops that enters through leaf edges and water pores, causing distinctive V-shaped yellow wedges that point toward the leaf's blackened veins.
- Hosts
- Cabbage, Broccoli, Cauliflower, Kale
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
Calcium deficiency
N/A — abiotic (nutrient deficiency/transport disorder)
Calcium barely moves within the plant once deposited, so deficiency symptoms show up specifically in the newest growth and fastest-growing tissue, most famously as blossom end rot on fruit.
- Hosts
- Tomato, Pepper, Cabbage, Lettuce
Clubroot
Plasmodiophora brassicae
A soilborne organism (technically a protist, long grouped with fungal diseases) that infects brassica roots and causes grotesque, swollen, club-shaped galls that cripple water and nutrient uptake.
- Hosts
- Cabbage, Broccoli, Cauliflower, Kale
Fruit cracking
N/A — abiotic (rapid water uptake after drought)
A dry spell followed by heavy rain or watering causes the fruit's interior to swell faster than the skin can stretch, splitting the skin in radial or concentric rings.
- Hosts
- Tomato, Watermelon, Cantaloupe / Melon, Cabbage
Fusarium crown and root rot
Fusarium oxysporum f. sp. radicis-lycopersici (and related formae)
A close relative of Fusarium wilt that attacks the crown and root system rather than moving up the whole vascular system, causing a brown, sunken canker right at the soil line.
- Hosts
- Tomato, Cucumber, Watermelon
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
Late blight
Phytophthora infestans
The water-mold pathogen behind the Irish potato famine. Moves explosively in cool, wet weather, turning whole tomato and potato plantings to black mush within days.
- Hosts
- Tomato, Potato
Lesion nematode
Pratylenchus spp.
A migratory soilborne roundworm that tunnels through roots (rather than settling in one spot like root-knot nematode), leaving dead, discolored lesions that open the door to fungal and bacterial rot organisms.
- Hosts
- Potato, Carrot, Strawberry, Apple
Phytophthora blight
Phytophthora capsici
A soil- and water-borne mold that causes sudden crown collapse and a fast-spreading fruit rot, especially devastating in low or poorly drained spots after heavy rain.
- Hosts
- Pepper, Zucchini, Winter squash, Pumpkin
Phytophthora root rot
Phytophthora spp.
A general term for water-mold root rots affecting perennials and fruiting shrubs/trees planted in soil that stays wet, slowly killing the root system from the tips inward.
- Hosts
- Strawberry, Raspberry, Blueberry, Apple
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
Pythium damping-off
Pythium spp.
A water mold that attacks seeds and seedlings in cool, wet, poorly drained soil, causing seeds to rot before they emerge or newly emerged seedlings to collapse at the soil line.
- Hosts
- Tomato, Pepper, Cucumber, Bush bean
Rhizoctonia root and crown rot
Rhizoctonia solani
A very common soil fungus that attacks seedlings at the soil line (a major cause of damping off) and, in older plants, causes root/crown rot and — on potato — the black, tar-like 'black scurf' on tubers.
- Hosts
- Bush bean, Potato, Cabbage, Lettuce
Ring rot of potato
Clavibacter sepedonicus
A quarantine-significant potato bacterium that plugs the vascular ring inside the tuber with a cheesy, cream-colored rot, usually spread from infected seed potatoes rather than the field.
- Hosts
- Potato
Root-knot nematode
Meloidogyne spp.
A microscopic soilborne roundworm that burrows into roots and triggers swollen galls as the plant's cells are hijacked to feed the nematode. Above-ground symptoms mimic drought or nutrient stress, which makes it easy to misdiagnose without pulling a plant.
- Hosts
- Tomato, Carrot, Cucumber, Pepper
Salt burn
N/A — abiotic (salt toxicity)
Excess soluble salts in the soil, from over-fertilizing, road salt runoff, or naturally saline soil/water, pull moisture out of roots and scorch leaf margins.
- Hosts
- Lettuce, Bush bean, Carrot, Strawberry
Soil compaction stress
N/A — abiotic (physical root restriction)
Repeated foot traffic, tilling wet soil, or heavy equipment presses soil particles together, squeezing out the pore space roots need to grow and water needs to drain through.
- Hosts
- Carrot, Potato, Tomato, Bush bean
Southern blight
Sclerotium rolfsii
A fast, heat-loving soil fungus that girdles the stem right at the soil line, identifiable by a white fan of fungal threads and mustard-seed-sized round sclerotia at the plant's base.
- Hosts
- Tomato, Pepper, Bush bean, Watermelon
Tipburn
N/A — abiotic (localized calcium deficiency)
Fast-growing inner leaves of heading crops outpace the plant's ability to deliver calcium to the leaf margin, so the very edge of the leaf dies while the rest stays healthy.
- Hosts
- Lettuce, Cabbage, Kale
White mold (Sclerotinia)
Sclerotinia sclerotiorum
A fungus that infects through dying blossoms, then colonizes stems and pods with a fluffy white cotton-like growth studded with hard black sclerotia the size of mouse droppings.
- Hosts
- Bush bean, Zucchini, Winter squash, Cabbage
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