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Diseases of Azalea
(Rhododendron spp.)

D. M. Benson, primary collator (last update 05/29/2015)

ALGAL DISEASE

Leaf spot and stem gall

Cephaleuros virescens Kunze ex E. M. Fries

FUNGAL DISEASES

Anthracnose

Glomerella cingulate (Stoneman) Spauld. & Schrenk

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

Armillaria root rot (Shoestring root rot)

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

          (syn. Rhizomorpha subcorticalis Pers. ex Gray)

Botrytis petal blight

Botrytis cinerea Pers.:Fr.

          (syn. Botryotinia fuckeliana [de Bary] Whetzel)

Bud and twig blight

Pycnostysanus azalea (Peck) E. W. Mason

          (syn. Briosia azaleae Peck)

Cercospora leaf spot

Cercospora handeliiHemmi & Kurata

          (syn. Pseudocercospora handelii [Bubák] Deighton)

Clitocybe root rot (Mushroom root rot)

Armillaria tabescens (Scop.) Emel.

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

Cylindrocladium blight and root rot

Cylindrocladium floridanum Sobers & C. P. Seym.

          (syn. Calonectria kyotensis Terash.)

Cylindrocladium parasiticum Crous, M. J. Wingf., & Alfenas.

Cylindrocladium scoparium Morgan

          (syn. Calonectria morganii Crous, Alfenas, & M. J. Wingf.)

Cylindrocladium theae (Petch) Subram.

          (syn. Calonectria indusiata [Seaver] Crous)

Damping-off, Pythium

Pythium spp.

P. irregular Buisman

Damping-off, Rhizoctonia

Rhizoctonia solani J. G. Kühn

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

Exobasidium yellow leaf spot

Exobasidium burtii Zeller

Leaf and flower gall

Exobasidium vaccinii (Fuckel) Woronin

          (syn. E. azalea Peck)

Leaf rust

Chrysomyxa reticulate P. E. Crane

Thekopsora minima Syd. & P. Syd.

          (syn. Pucciniastrum minimum Arthur)

Leaf scorch

Phloeospora azaleae (Voglino) Priest

          (syn. Septoria azalea Voglino)

Ovulinia petal blight

Ovulinia azaleae Weiss

          (syn. Ovulitis azaleaeN. F. Buchw.)

Pestalotiopsis leaf spot and twig blight

Pestalotiopsis sydowiana (Bres.) B. Sutton

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

Phomopsis dieback

Phomopsis spp.

Phyllosticta leaf spot

Phyllosticta rhododendri West.

Phytophthora blight and dieback

Phytophthora citricola Sawada

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

P. foliorum Donahoo & Lamour

P. hibernalis Carne

P. nicotianae Breda de Haan

          (syn. P. parasitica Dastur)

P. pseudosyringae Jung & Delatour

P. syringae (Berk.) Kleb.

Phytophthora root rot

Phytophthora cinnamomi Rands (P. cinnamomi var. cinnamomi)

P. nicotianae Breda de Haan

          (syn. P. parasitica Dastur)

Powdery mildew

Erysiphe azaleae (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.

Shoot or twig blight

Monilinia azaleae Honey

Web blight

Ceratobasidium ramicola Tu, D. A. Roberts, & Kimbr.

          (syns. Ceratorhiza ramicola [W. A. Weber & D. A. Roberts]
           R. T. Moore; Rhizoctonia ramicola G. F. Weber & D. A. Roberts)

Rhizoctonia spp. (binucleate)

          (syn. Ceratobasidium D. P. Rogers)

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.

UNDETERMINED ETIOLOGY

Witches’-broom

Undetermined