Host Plants - Westcott's Plant Disease - page 618

B LIGHT , Cutting. Cylindrocladium scoparium
and C. floridanum, FL, OH.
B LIGHT , Flower Spot. Ovulinia azaleae, CA, SC.
B LIGHT , Gray. Pestalotia macrotricha, general
after winter injury.
B LIGHT , Necrotic Shoots and Leaves.
Phytophthora irrigate and P. hydropathica,
MD, PA, VA, WV.
B LIGHT , Silky Thread. Rhizoctonia ramicola,
FL.
B LIGHT ,Twig. Phomopsis sp., CT, NJ, NY, OR;
Phytophthora hedraiandra, PA.
C ANKER ;D IEBACK . Botryosphaeria ribis,MD,
MA, NJ, NY; Gloeosporium sp., MD, NY;
Phytophthora cactorum, MD, MA, NJ, NY,
OH, PA, RI; P. hedraiandra (also leaf
lesions), MN; Glomerella cingulata, MD;
Phytophthora cambivora, NC.
D AMPING -O FF . Alternaria sp., CT; Rhizoctonia
solani, CT, NJ, NY.
D ODDER . Cuscuta gronovii, NJ.
G ALL . Exobasidium vaccinii, leaf and shot,
MA to FL, MS; E. burtii, yellow leaf spot,
NJ; E. vaccinii-uliginosae, Witches' Broom,
NJ.
L EAF S POT . Cercospora handelii, FL, NJ, NC,
VA; Coryneum rhododendri,NC,PA,TN,
VA; Cryptostictis mariae, KY, NY, TN, VA;
Discosia artocreas, secondary, MD, NY;
Guignardia rhodorae, CT, MD, MA, NJ,
NY, PA, VA; Gloeosporium ferrugineum,
NC; Hendersonia concentrica, NC, TX,
WV; Lophodermium schweinitzii,NYto
NC, TX; Pestalopezia rhododendri,TN,
WV; Mycosphaerella clintoniana, NJ, NY,
NC, OR, WA; Phyllosticta rhododendri,NJ;
Physalospora rhododendri,PA,TN,VA;
Phomopsis rhododendri, N ; Septoria
rhododendri,ME,NC;S. solitaria,N ;
Venturia rhododendri, MD, VA;
Phytophthora inflata,OH;P. insolita,OH.
L EAF S POT , Tar. Melasmia rhododendri, AK.
N ONPARASITIC . Chlorosis. Mineral deficiency,
usually iron, widespread.
Sunscald; Windburn. Severe winter injury in
exposed locations.
Walnut Toxicity. Poisoning by root emanation
from Juglans nigra .

P OWDERY M ILDEW . Microsphaera alni, MD, NJ,
NY; Erysiphe azalea and E. vaccinii, Pacific
Northwest.
R OT , Heart; Wood Rot. Fomes annosus, NC.
R OT , Root. Armillaria mellea, CA, NJ, NY;
Phymatotrichum omnivorum, TX.
R UST . Chrysomyxa ledi var. rhododendri, CA,
WA; C. roahnensis (II, III), NC, TN; 0, I on
spruce; C. piperiana (II, III), CA, OR, WA;
Pucciniastrum vaccinii (II), CT, NJ, RI.
S POT A NTHRACNOSE . Sphaceloma sp., WA.
V IRUS . Rhododendron Necrotic Ringspot,OR.
W ILT . Phytophthora cambivora, NC;
P. cinnamomi, MD, NJ, NY, PA, OH, VA;
P. citricola, OH, VA; P. cactorum, VA;
P. citrophthora, VA; P. nicotianae, VA;
P. tropicalis, VA; P. hibernalis.
Most rhododendron leaf spots are not worth
worrying about. Some come after winter injury;
some are definitely parasitic but not serious. Win-
ter and early spring sun will turn some of the
foliage brown. Do not prune out supposedly
dead twigs and branches too soon; wait for new
growth to start. An accumulation of matted wet
leaves around the trunk fosters root and collar rot.
Be cautious in the use of aluminum sulfate to
acidify soil; sulfur is somewhat safer.

Rhoeo

V IRUS , Tobacco Mosaic, MD.

Rhubarb (Rheum)

A NTHRACNOSE . Colletotrichum sp., IL, MO, PA,
WV, WI.
B ACTERIAL Crown Gall. Agrobacterium

tumefaciens, IA, MA, NY.
B ACTERIAL Soft Rot. Erwinia carotovora, occa-
sional in market; E. rhapontici, crown
rot, OK.
B LIGHT , Southern. Sclerotium rolfsii, FL, MS,
TX, VA.
D AMPING -O FF ; Crown Rot. Pythium spp.,

CA, MD.
D OWNY M ILDEW . Peronospora rumicis, CA.