Diseases

Venturia inaequalis

The most widespread apple disease in humid regions. Reduces fruit quality and defoliates trees.

Podosphaera and Sphaerotheca species

Surface-feeding fungal disease producing white powdery growth on leaves and fruit, particularly damaging on gooseberries.

Apiosporina morbosa

Fungal disease producing characteristic black warty galls on plum and cherry branches.

Botryosphaeria dothidea

Fungal disease that enters through wounds and kills entire stems or whole bushes, particularly damaging on young plantings in the southeastern US.

Monilinia fructicola

The most damaging stone-fruit and almond disease, causing blossom blight and fruit rot.

Elsinoe veneta

Fungal cane disease causing purple-bordered lesions that girdle and weaken bramble and Ribes canes, reducing yield over consecutive seasons.

Leptosphaeria coniothyrium

Fungal disease that enters through wounds (often from cane-borer or pruning cuts) and causes dark cankers that wilt and kill canes.

Gymnosporangium juniperi-virginianae

Two-host fungal disease alternating between apple and eastern red cedar. Severe pressure in regions with abundant cedar.

Blumeriella jaapii

Defoliating fungal disease that weakens trees over consecutive seasons.

Cryphonectria parasitica

The fungus that destroyed the American chestnut population in the early 20th century. Chinese chestnuts and most modern hybrids are tolerant; American chestnut remains susceptible.

Plasmodiophora brassicae

Soil-borne disease causing characteristic distorted club-shaped roots on brassicas. Persists in soil for 10-20 years; the dominant brassica pathogen in acidic poorly-drained soils.

Ustilago maydis

Fungal disease that produces large gray-black galls on corn ears and stalks. Considered a delicacy (huitlacoche) in Mexican cuisine.

Pythium and Rhizoctonia species

Soil-borne complex of water molds and fungi that kill seedlings before or shortly after emergence. The single most common cause of seed-starting failures.

Pseudoperonospora cubensis (cucurbits) and others

Water mold (oomycete, not a true fungus) that thrives in cool damp conditions. Spreads rapidly through cucurbit and brassica plantings on wind-borne spores.

Alternaria solani

Fungal disease starting on lower leaves and progressing upward. The most common tomato and potato leaf disease in the eastern US.

Anisogramma anomala

Native fungal disease of American hazelnut that devastates European hazelnut plantings, the limiting factor for commercial hazelnut culture in the East.

Puccinia sambuci

Two-host rust alternating between elderberry and sedges, causing leaf spots and shoot distortion in spring.

Cerotelium fici

Late-season rust disease causing defoliation in humid southeastern conditions.

Fusarium oxysporum

Soil-borne fungal disease that plugs vascular tissue and kills affected plants. Persists in soil for many years; impossible to eliminate once established.

Botrytis cinerea

Ubiquitous fungal disease that causes fruit rot during cool wet weather, often the dominant berry disease in humid regions.

Phytophthora infestans

The pathogen responsible for the Irish Potato Famine. Devastating in cool wet weather; can destroy a tomato planting in days.

Colletotrichum gloeosporioides

Most damaging mango disease worldwide. Fungal spores infect blossoms and developing fruit during humid weather, producing black sunken lesions that expand on ripening fruit.

Monilinia vaccinii-corymbosi

The most damaging blueberry disease in the eastern US, killing shoots in spring and mummifying fruit later in the season.

Sclerotium cepivorum

Soil-borne fungal disease specific to alliums. Sclerotia survive 20+ years in soil; once present, the disease persists indefinitely in that bed.

Arthuriomyces peckianus

Systemic fungal disease that permanently infects black raspberries and blackberries (not red raspberry); infected plants must be removed entirely.

Fusarium oxysporum f. sp. cubense

Soil-borne fungus that colonizes banana root and vascular tissue, causing irreversible wilt. Tropical Race 4 is currently spreading globally and threatens the Cavendish industry. Survives in soil for decades.

Taphrina deformans

Distinctive springtime disease causing red, puckered leaves. Manageable with one well-timed dormant spray.

Venturia pyrina

Fungal disease similar to apple scab but specific to pear, causing leaf and fruit lesions.

Venturia effusa

The most damaging pecan disease in the humid Southeast, causing leaf and nut lesions that reduce yield and kernel quality.

Phytophthora species

Soil-borne water mold that destroys roots in waterlogged soils, the leading cause of blueberry decline in poorly drained sites.

Pseudocercospora punicae

Fungal disease causing leaf and fruit blotches in humid pomegranate-growing regions.

Podosphaera leucotricha

Surface-feeding fungal disease that distorts new growth and reduces yields.

Phytophthora fragariae

Soil-borne water mold that destroys strawberry roots in wet cool springs, characterized by red discoloration in the root core.

Septoria lycopersici

Fungal disease that defoliates tomato from the bottom up. Doesn't directly affect fruit but reduces yield through loss of leaf area.

Capnodium spp.

Black fungal coating that grows on honeydew secreted by aphids, scale, mealybugs, and whiteflies. Doesn't infect plant tissue directly but blocks photosynthesis and disfigures fruit.

Sclerotium rolfsii

Soil-borne fungal disease most damaging in warm humid Southern conditions. White mycelial fans and small mustard-seed-sized sclerotia at the soil line are diagnostic.

Didymella applanata

Fungal disease that produces purple-brown lesions at leaf nodes on red and yellow raspberry canes, weakening fruiting laterals.

Colletotrichum acutatum

Aggressive fungal disease that causes fruit rot, crown rot, and runner lesions in strawberries, devastating during warm wet weather.

Mycosphaerella fragariae

Common fungal disease producing characteristic small purple spots with white centers on strawberry leaves.

Geosmithia morbida (vectored by Pityophthorus juglandis)

Fatal disease of black walnut caused by a fungus vectored by the walnut twig beetle. Spreading eastward from the western US, devastating native black walnut stands.

Multiple species (Erysiphales)

Surface-feeding fungal disease producing white powdery growth on leaves and stems. Reduces yield by stealing photosynthate and accelerating senescence.

Verticillium dahliae

Soil-borne fungal disease similar to fusarium wilt but with broader host range and cooler temperature optimum. Persists in soil for 10+ years.

Ophiognomonia leptostyla

Fungal leaf disease causing premature defoliation in wet seasons, weakening trees over consecutive years and reducing kernel fill.

Sclerotinia sclerotiorum

Fungal disease that produces fluffy white mycelium on stems and lower leaves. Forms hard black sclerotia (resting bodies) that survive 5+ years in soil.

Cronartium ribicola

Two-host rust requiring both Ribes (currants and gooseberries) and white pines. Historically led to Ribes-planting bans in much of the US; some states still restrict black currant cultivation.

Xylella fastidiosa

Bacterial disease vectored by sharpshooter leafhoppers, causing progressive leaf scorch and tree decline. Same pathogen species as Pierce's disease in grape.

Pseudomonas syringae

Bacterial disease causing limb dieback and gummosis, particularly damaging in wet cool springs.

Xanthomonas arboricola pv. corylina

Bacterial disease that kills young hazelnut trees and damages established plantings, particularly during wet establishment.

Xanthomonas arboricola pv. pruni

Bacterial disease causing leaf spots and fruit blemishes, severe in warm humid regions.

Xanthomonas euvesicatoria and X. perforans

Bacterial disease causing leaf spots and fruit blemishes on pepper and tomato. Severe in warm humid weather, transmitted via splashing water and seed.

Erwinia tracheiphila

Bacterial disease vectored exclusively by cucumber beetles. Once a plant is infected there is no recovery; whole-plant collapse follows.

Xanthomonas citri

Bacterial disease producing raised corky lesions on leaves, twigs, and fruit. Spread by wind-driven rain and contaminated tools. Quarantine-regulated in many areas.

Candidatus Liberibacter asiaticus

Devastating bacterial disease vectored by the Asian citrus psyllid. Once infected, trees decline progressively over several years and there is no cure. Has destroyed commercial citrus across Florida and threatens production worldwide.

Agrobacterium tumefaciens

Soil-borne bacterium that enters plants through wounds and induces tumor-like galls on roots, crown, and lower stems. Galls reduce vigor and shorten plant lifespan; on Rubus the disease is often fatal.

Erwinia amylovora

Devastating bacterial disease that can kill trees rapidly. Most severe in warm wet springs.

Cucumber mosaic virus, Tobacco mosaic virus, and others

Family of plant viruses producing mottled yellow-and-green leaf patterns. Vectored primarily by aphids; some are seed-transmitted or spread by handling tools and tobacco products.

Tomato spotted wilt orthotospovirus (TSWV)

Virus vectored by thrips, particularly western flower thrips. Wide host range and growing global distribution. No cure once infected.

Calcium deficiency physiological disorder

Not a true disease but a calcium-uptake disorder caused by inconsistent soil moisture during fruit development. The dominant cause of damaged first-fruit on home tomato plantings.

Yeast and bacterial complex

Souring of ripe fig fruit caused by microorganisms entering through the open eye, particularly in humid conditions.

Physiological disorder

Damage from direct intense sun exposure on fruit or bark, particularly on plants suddenly exposed by pruning, defoliation, or hot weather. Distinct from sunburn (which is reversible).