Plant disease & disorder profiles
Showing 74 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 leaf streak
Xanthomonas translucens
A bacterium of cereal grains and some leafy crops that produces long, water-soaked streaks running parallel to the leaf veins, which dry into a dark, brittle stripe.
- Hosts
- Corn, Wheat
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 speck
Pseudomonas syringae pv. tomato
A cool-weather bacterium that produces tiny, dark, pinprick-sized specks on tomato leaves and fruit, often surrounded by a thin yellow halo.
- Hosts
- Tomato
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
Bacterial wilt of cucurbits
Erwinia tracheiphila
A bacterium spread almost exclusively by cucumber beetles, which introduce it while feeding. It clogs the plant's water-conducting vessels, causing a sudden, irreversible wilt.
- Hosts
- Cucumber, Cantaloupe / Melon, Zucchini, Winter squash
Bean common mosaic virus
Bean common mosaic virus (BCMV)
A seedborne and aphid-transmitted virus that mottles bean leaves and can distort pods, one of the most common bean diseases worldwide.
- Hosts
- Bush bean, Pole bean
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
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
Catfacing
N/A — abiotic (cold-triggered flower deformity)
Cold temperatures during flower formation damage part of the blossom, and the fruit that develops from it grows scarred, puckered, and deeply lobed at the blossom end.
- Hosts
- Tomato, Pepper
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
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
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
Corn smut
Ustilago maydis
A striking fungus that replaces developing corn kernels (and sometimes tassels) with large gray-silver galls filled with sooty black spores; in some cuisines the young galls are harvested as a delicacy (huitlacoche).
- Hosts
- Sweet corn
Crown gall
Agrobacterium tumefaciens
A soil bacterium that inserts a piece of its own DNA into the plant's cells at wound sites, tricking the plant into growing rough, woody tumor-like galls, most often at the crown or graft union.
- Hosts
- Apple, Grape, Raspberry, Blueberry
Cucumber mosaic virus
Cucumber mosaic virus (CMV)
One of the most widespread plant viruses, with an enormous host range spanning vegetables, ornamentals, and weeds. Aphids spread it quickly through a garden even without settling long on any one plant.
- Hosts
- Cucumber, Zucchini, Winter squash, Pepper
Cucurbit yellow stunting disorder
Cucurbit yellow stunting disorder virus (CYSDV)
A whitefly-transmitted virus that causes older cucurbit leaves to yellow between the veins while veins stay green, sapping vigor and sugar content late in the season.
- Hosts
- Cantaloupe / Melon, Cucumber, Watermelon, Zucchini
Curly top virus
Beet curly top virus (BCTV)
A leafhopper-vectored virus common in hot, dry western regions that causes dramatic upward leaf curling, stunting, and often plant death, especially on tomato and bean.
- Hosts
- Tomato, Pepper, Bush bean
Downy mildew (basil)
Peronospora belbahrii
A basil-specific water mold that causes leaf yellowing that looks like a nutrient problem at first, until the telltale gray-brown fuzz appears on the underside.
- Hosts
- Basil
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
Edema (oedema)
N/A — abiotic (water-uptake imbalance)
Roots take up water faster than leaves can transpire it away (common in cool, humid, low-light conditions), so leaf cells swell and burst, leaving small corky bumps.
- Hosts
- Tomato, Cabbage, Potato
Fire blight
Erwinia amylovora
A fast-moving bacterium of apples, pears, and their relatives that scorches blossoms, shoots, and branches so they look burned, giving the disease its name.
- Hosts
- Apple, Pear
Frost / chill injury
N/A — abiotic (cold temperature injury)
Ice formation inside plant cells (frost) or prolonged cold below a crop's tolerance (chilling, even above freezing for warm-season crops) ruptures cells and disrupts normal metabolism.
- Hosts
- Tomato, Pepper, Zucchini, Cucumber
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
Fusarium wilt
Fusarium oxysporum (host-specific formae speciales)
A soilborne fungus that invades roots and clogs the plant's water-conducting tissue from the inside, causing one-sided or whole-plant wilting that doesn't recover even with watering.
- Hosts
- Tomato, Watermelon, Cantaloupe / Melon, Pepper
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
Herbicide drift injury
N/A — abiotic (chemical injury)
Herbicide applied nearby (on a lawn, roadside, or neighboring field) drifts on wind or volatilizes in heat and lands on garden plants, causing characteristic twisting and cupping, especially from broadleaf herbicides like 2,4-D or dicamba.
- Hosts
- Tomato, Pepper, Grape
Iron deficiency
N/A — abiotic (nutrient deficiency)
Iron is nearly immobile in the plant, so deficiency shows up first and most severely on the youngest leaves, turning them pale yellow to white while veins stay sharply green. Usually a soil pH problem, not a true lack of iron.
- Hosts
- Blueberry, Raspberry, Strawberry, Tomato
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
Lettuce mosaic virus
Lettuce mosaic virus (LMV)
A seedborne and aphid-transmitted virus that stunts lettuce and mottles its leaves, a serious quality problem since even light infection makes heads unmarketable.
- Hosts
- Lettuce
Magnesium deficiency
N/A — abiotic (nutrient deficiency)
Magnesium sits at the center of every chlorophyll molecule, so a shortage causes distinctive yellowing between the leaf veins on older leaves, while the veins themselves stay green.
- Hosts
- Tomato, Pepper, Grape, Zucchini
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
Peach leaf curl
Taphrina deformans
A fungus that infects peach and nectarine buds before they even open in spring, causing dramatically puckered, reddened, distorted new leaves as soon as they emerge.
- Hosts
- Peach
Phosphorus deficiency
N/A — abiotic (nutrient deficiency)
Phosphorus deficiency shows up most dramatically as a purple-red pigment building up in older leaves, especially on the undersides and veins, most visible in cool soil that slows phosphorus uptake.
- Hosts
- Corn, Tomato, Pepper
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
Potassium deficiency
N/A — abiotic (nutrient deficiency)
Potassium moves within the plant like nitrogen, so a shortage shows up as scorched, yellowing leaf margins on the oldest leaves first, while the leaf interior often stays green longer.
- Hosts
- Tomato, Potato, Pepper, Watermelon
Potato scab
Streptomyces scabies
A soil actinomycete (bacteria-like organism, long managed alongside fungal diseases) that roughens potato tuber skin with corky, scabby lesions. Cosmetic mostly — tubers are still edible once peeled.
- Hosts
- Potato
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
Powdery mildew
Podosphaera/Erysiphe/Golovinomyces spp. (host-specific species)
Unmistakable white-gray powdery coating on leaf surfaces, caused by several host-specific fungal species. Unlike most fungal diseases it thrives in dry air and doesn't need free water on the leaf to infect.
- Hosts
- Zucchini, Winter squash, Pumpkin, Cucumber
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
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
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
Squash mosaic virus
Squash mosaic virus (SqMV)
A seedborne and beetle-transmitted virus of cucurbits producing sharp mosaic mottling and often severe fruit distortion, more disfiguring on fruit than cucumber mosaic virus.
- Hosts
- Zucchini, Winter squash, Pumpkin, Cucumber
Sulfur deficiency
N/A — abiotic (nutrient deficiency)
Sulfur deficiency looks a lot like nitrogen deficiency, an overall pale yellowing, but unlike nitrogen it shows up on the youngest leaves first since sulfur is less mobile within the plant.
- Hosts
- Cabbage, Broccoli, Onion, Corn
Sunscald
N/A — abiotic (heat/UV injury)
Direct sun exposure on fruit that's lost its protective leaf canopy (from disease, pruning, or wilting) bleaches and blisters the exposed skin.
- Hosts
- Tomato, Pepper, Apple
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
Tobacco/tomato mosaic virus
Tobacco mosaic virus (TMV) / Tomato mosaic virus (ToMV)
A remarkably stable virus that mottles leaves in patches of light and dark green and stunts growth. It survives for years in dried plant debris and even in tobacco products, which is one of its unusual routes into a garden.
- Hosts
- Tomato, Pepper
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
Transplant shock
N/A — abiotic (root disturbance stress)
Moving a plant from a container or one location to another damages fine roots and abruptly changes light, temperature, and moisture, so the plant wilts and stalls until new roots establish.
- Hosts
- Tomato, Pepper, Lettuce, Cabbage
Verticillium wilt
Verticillium dahliae
A cool-weather cousin of Fusarium wilt with an enormous host range (over 200 plant species), clogging the vascular system and producing distinctive V-shaped yellow wedges on leaves.
- Hosts
- Tomato, Potato, Eggplant, Pepper
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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