The following is a list of diseases of pears (Pyrus communis).
| Bacterial diseases | |
|---|---|
| Crown gall | Agrobacterium tumefaciens |
| Erwinia amylovora | |
| Pseudomonas blossom blast and canker | Pseudomonas syringae pv. syringae |
| Pear decline | Phytoplasma |
| Fungal diseases | |
|---|---|
| Alternaria fruit rot | Alternaria spp. |
| Anthracnose canker and bull's-eye rot | Pezicula malicorticus Cryptosporiopsis curvispora [anamorph] |
| Armillaria root rot (shoestring root rot) | Armillaria mellea Rhizomorpha subcorticalis [anamorph] |
| Bitter rot | Glomerella cingulata Colletotrichum gloeosporioides [anamorph] |
| Black rot, leaf spot and canker | Botryosphaeria obtusa Sphaeropsis malorum [anamorph] |
| Black spot (of Japanese pear) | Alternaria alternata |
| Blister canker | Helminthosporium papulosum |
| Blister disease | Coniothecium chomatosporum |
| Blue mold rot | Penicillium spp. Penicillium expansum |
| Botrytis spur and blossom blight | Botrytis cinerea Botryotinia fuckeliana [teleomorph] |
| Brown rot | Monilinia fructicola Monilinia laxa |
| Cladosporium fruit rot | Cladosporium herbarum Mycosphaerella tassiana [teleomorph] |
| Clitocybe root rot (mushroom root rot) | Armillaria tabescens Clitocybe tabescens |
| Coprinus rot | Coprinopsis psychromorbida |
| Dematophora root rot (Rosellinia root rot) | Rosellinia necatrix Dematophora necatrix [anamorph] |
| Diplodia canker | Botryosphaeria stevensii Physalospora malorum Diplodia mutila [anamorph] |
| Elsinoe leaf and fruit spot | Elsinoe piri Sphaceloma pirinum [anamorph] |
| European canker | Nectria galligena Cylindrocarpon heteronemum [anamorph] |
| Fabraea leaf and fruit spot | Diplocarpon mespili Fabraea maculata Entomosporium mespili [anamorph] |
| Fly speck | Schizothyrium pomi Zygophiala jamaicensis [anamorph] |
| Gibberella canker | Gibberella baccata Fusarium lateritium [anamorph] |
| Gray mold rot | Botrytis cinerea |
| Late leaf spot | Cercospora minima |
| Mucor fruit rot | Mucor spp. Mucor piriformis |
| Mycosphaerella leaf spot (ashy leaf spot and fruit spot) | Mycosphaerella pyri Mycosphaerella sentina Septoria pyricola [anamorph] |
| Nectria twig blight (coral spot) | Nectria cinnabarina Tubercularia vulgaris [anamorph] |
| Pear scab | Venturia pyrina Fusicladium pyrorum [anamorph] |
| Perennial canker | Neofabraea perennans Cryptosporiopsis perennans [anamorph] |
| Phyllosticta leaf spot | Phyllosticta sp. |
| Phytophthora crown and root rot (sprinkler rot) | Phytophthora cactorum |
| Pink mold rot | Trichothecium roseum Cephalothecium roseum |
| Powdery mildew | Podosphaera leucotricha |
| Pythium dieback | Pythium spp. |
| Rhizopus rot | Rhizopus stolonifer |
| Rust, American hawthorne | Gymnosporangium globosum |
| Rust, Kern's pear | Gymnosporangium kernianum |
| Rust, Pacific Coast pear | Gymnosporangium libocedri |
| Rust, pear trellis (European pear rust) | Gymnosporangium fuscum |
| Rust, Rocky Mountain pear | Gymnosporangium nelsonii |
| Side rot | Phialophora malorum |
| Silver leaf | Chondrostereum purpureum |
| Sooty blotch | Gloeodes pomigena |
| Thread blight (Hypochnus leaf blight) | Corticium stevensii Pellicularia koleroga Hypochnus ochroleucus |
| Valsa canker | Valsa ceratosperma Cytospora sacculus [anamorph] |
| Wood rot | Trametes versicolor and various basidiomycetes |
| Xylaria root rot | Xylaria spp. |
| Miscellaneous diseases and disorders | |
|---|---|
| Alfalfa greening (green stain) | Unknown |
| Bitter pit | Localized calcium deficiency |
| Black end | Water imbalance |
| Black speck (skin speckling) | Associated with low oxygen in storage |
| Blossom blast | Boron deficiency |
| Brown core | High CO2 |
| Core breakdown (Bartlett) | Senescence |
| Cork spot | Associated with calcium deficiency |
| Green stain | Unknown |
| Internal bark necrosis | Unknown |
| Mealy core (d`Anjou) | Senescence |
| Pink end (Bartlett) | Preharvest low temperature |
| Rosette | Unknown |
| Scald | Senescence |
| Nematodes, parasitic | |
|---|---|
| Dagger, American | Xiphinema americanum |
| Dagger | Xiphinema riveri Xiphinema vuittenezi |
| Lesion | Pratylenchus spp. Pratylenchus penetrans |
| Pin | Paratylenchus spp. |
| Root-knot | Meloidogyne spp. |
| Viruslike diseases | |
|---|---|
| Flemish beauty corky pit | Virus suspected |
| Pear blister canker | Virus suspected |
| Pear decline | Phytoplasma |
| Pear freckle pit | Virus suspected |
| Pear red mottle | Virus suspected |
| Pear ring pattern mosaic | Virus suspected |
| Pear rough bark | Virus suspected |
| Pear stony pit | Virus suspected |
| Pear vein yellows | Virus suspected |
| Quince bark necrosis | Virus suspected |
| Quince sooty ring spot | Virus suspected |
| Quince stunt | Virus suspected |
| Quince yellow blotch | Virus suspected |