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Diseases of Rhododendron
(Rhododendron spp.)

D. M. Benson, primary collator (last update 5/29/2015)

ALGAL DISEASE

Leaf spot and stem gall

Cephaleuros virescens Kunze ex E. M. Fries

BACTERIAL DISEASE

Crown gall

Agrobacterium tumefaciens (Smith & Townsend) Conn

FUNGAL DISEASES

Armillaria root rot (Shoestring root rot)

Armillaria mellea (Vahl:Fr.) P. Kumm.

          (syn. Rhizomorpha subcorticalis Pers. ex Gray)  

Botryosphaeria dieback

Botryosphaeria dothidea (Moug.:Fr.) Ces. & de Not.

          (syn. Fusicoccum aesculi Corda)

Botrytis leaf and petal blight

Botrytis cinerea Pers.:Fr.

          (syn. Botryotinia fuckeliana [de Bary] Whetzel)

Bud and twig blight

Pycnostysanus azalea (Peck) W. E. Mason

          (syn. Briosia azalea [Peck] Dearn.)

Cercospora leaf spot

Cercospora handelii Hemmi & Kurata

          (syn. Pseudocercospora handelii [Bubák] Deighton)

Chrysomyxa leaf rust

Chrysomyxa nagodhii P. E. Crane

C. reticulata P. E. Crane

C. roanensis (Arthur) Arthur

Peridermium parksianum Faull

          (syn. C. piperiana Sacc. & Trott. ex Cummins)

Clitocybe root rot (Mushroom root rot)

Armillaria tabescens (Scop.) Emel

          (syn. Clitocybe tabescens [Scop.] Bres.)

Colletotrichum leaf spot

Glomerella cingulata (Stoneman) Spauld. & Schrenk

          (syn. Colletotrichum gloeosporioides [Penz.] Penz. & Sacc.)

Coryneum leaf spot

Seimatosporium rhododendri (Schwein.) Piroz. & Shoemaker

          (syn. Coryneum rhododendri Schwein.)

Cryptostictis leaf spot

Seimatosporium mariae (Clinton) Shoemaker

          (syns. Cryptostistis mariae [Clinton] Sacc.; Sarcostroma mariae
          [Clinton] Nag Raj)

Cylindrocarpon canker and wilt

Cylindrocarpon destructans var. destructans (Zinssm.) Scholten

                    (syn. C. radicicola Wollenw.)

Cylindrocladium stem canker

Cylindrocladium theae (Petch) Subram.

          (syn. Calonectria indusiata [Seaver] Crous)

Damping-off, Pythium

Pythium spp.

Damping-off, Rhizoctonia

Rhizoctonia solani J. G. Kühn

          (syn. Thanatephorus cucumeris [A. B. Frank] Donk)

Exobasidium yellow leaf spot

Exobasidium burtii Zeller

Glomerella canker and dieback

Glomerella cingulata (Stoneman) Spauld. & Schrenk

          (syn. Colletotrichum gloeosporioides [Penz.] Penz. & Sacc.)

Gray blight

Pestalotiopsis sydowiana (Bres.) B. Sutton

          (syns. Pestalotia sydowiana Bres.; Pestalotiopsis rhododendri
          Y. M. Zhang, Maharachch., & K. D. Hyde)

Leaf and flower gall

Exobasidium vaccinii (Fuckel) Woronin

          (syn. E. azalea Peck)

Lophodermium leaf spot

Lophodermium schweinitzii M. Wilson & N. F. Robertson

Ovulinia petal blight

Ovulinia azalea Weiss

          (syn. Ovulitis azaleae N. F. Buchw.)

Pestalosphaeria leaf spot

Pestalosphaeria concentrica M. E. Barr

          (syn. Pestalotiopsis guepini var. macrotricha [Kleb.] B. Sutton)

Pestalotiopsis leaf spot and twig blight

Pestalotiopsis sydowiana (Bres.) B. Sutton

          (syns. Pestalotia sydowiana Bres.; Pestalotiopsis rhododendri
          Y. M. Zhang, Maharachch., & K. D. Hyde)

Pestalotiopsis guepinii var. macrotricha (Kleb.) B. Sutton

          (syn. Pestalotia macrotricha Kleb.)

Phyllosticta leaf spot

Phyllosticta cunninghamiae Allesch.

Phymatotrichopsis root rot (Cotton root rot)

Phymatotrichopsis omnivora (Shear) Hennebert

          (syn. Phymatotrichum omnivorum [Shear] Duggar)

Phytophthora blight and dieback

Phytophthora cactorum (Lebert & Cohn) Schröt.

P. cambivora (Petri) Buisman

P. cinnamomi Rands (P. cinnamomi var. cinnamomi)

P. citricola Sawada

P. citrophthora (R. E. Sm. & E. H. Sm.) Leonian

P. gonapodyides (H. E. Petersen) Buisman

P. hedraiandra De Cock & Man in 't Veld

P. heveae A. Thomps.

P. hibernalis Carne

P. hydropathica Hong & Gallegly

P. inflata Caroselli & Tucker

P. insolita Ann & W. H. Ko

P. kernoviae Brasier, Beales, & S. A. Kirk

P. nicotianae Breda de Haan

          (syn. P. parasitica Dastur)

P. pini (Leonian) Gallegly, Hong, Richardson, & Kong

P. plurivora T. Jung & T. I. Burgess

P. ramorum Werres, De Cock, & Man in 't Veld

P. syringae (Berk.) Kleb.

P. tropicalis Aragaki & J. Y. Uchida

Phytophthora root rot

Phytophthora cactorum (Lebert & Cohn) Schröt.

P. cambivora (Petri) Buisman

P. cinnamomi var. cinnamomi Rands

P. citricola Sawada

P. cryptogea Pethybr. & Laff.

P. nicotianae Breda de Haan

          (syn. P. parasitica Dastur)

Powdery mildew

Erysiphe azalea (U. Braun) U. Braun & S. Takam.

E. digitata (A. J. Inman & U. Braun) A. J. Inman & U. Braun

E. izuensis (Y. Nomura) U. Braun & S. Takam.

E. rhododendri J. N. Kapoor

E. vaccinii Schwein.

Oidium ericinum Erikss.

Phyllactinia guttata (Wallr.:Fr.) Lév.

P. rhododendri H. D. Shin & Y. J. La.

Septoria leaf spot

Septoria rhododendri Cooke

Spot anthracnose

Sphaceloma spp.

Thekopsora leaf rust

Thekopsora minima Syd. & P. Syd.

          (syn. Pucciniastrum minimum Arthur)

Witches’-broom

Exobasidium vaccinii-uliginosi Boud.

NEMATODES (PARASITIC)

Foliar nematode:

Aphelenchoides fragariae (Ritzema Bos) Christie

Root-knot nematode:

Meloidogyne spp.

Stunt nematode:

Tylenchorhynchus claytoni Steiner

PARASITIC HIGHER PLANT

Dodder (Scaldweed)

Cuscuta gronovii Willd. ex Schult.

VIRUS DISEASES

Necrotic ringspot

Genus Potexvirus (Potato virus X group), Rhododendron necrotic ringspot virus (RoNRSV)

Other Viruses Causing Asymptomatic Infections

Petuvirus:

Rhododendron virus N (RhVN)

Unknown:

Rhododendron virus A (RhVA)