Plant disease & disorder profiles
Showing 35 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
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 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 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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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