Host Plants - Westcott's Plant Disease - page 542

B LIGHT , Southern; Crown Rot. Sclerotium rolfsii
( S. delphinii ), general.
L EAF S POT . Alternaria iridicola, IL, MT, TX,
WA WI; Didymellina macrospora
( Heterosporium iridis ); Ascochyta iridis
MD, NY; Cladosporium herbarum, second-
ary; Kabatiella microsticta, secondary;
Phyllosticta iridis, FL, MI, NY, OH, TX,
WI; Stictopatella iridis, IL.
N EMATODE , Root Knot. Meloidogyne incognita.
N ONPARASITIC . Scorch. Cause unknown, some-
times associated with nematodes.
R OT , Gray Mold; Crown. Botryotinia convoluta,
MN, NJ, NY, WI.
R OT , Root; Damping-Off. Rhizoctonia solani,
occasional.
R UST . Puccinia iridis (II, III), widespread on
native species; most garden varieties are resis-
tant. P. sessilis (0, I), ME to NE, MN; II, III on
Phalarus .
V IRUS . Iris Severe Mosaic; Iris Fulva Mosaic,
MA.
The most common disease of bearded iris in
home gardens is bacterial soft rot following
iris borer. Crown rot or southern blight gets
started when iris is too crowded. Didymellina
leaf spot or blight may be conspicuous in a wet
summer. The physiological () disease, scorch,
is causing concern, particularly in central
states.

Iresine (Blood-Leaf)

L EAF S POT . Septoria iresines, OK.
N EMATODE , Root Knot. Meloidogyne sp., FL,
MD.
R OT , Root. Helicobasidium purpureum, TX;
Rhizoctonia solani, IL.
S MUT , Inflorescence. Thecaphora iresine, IN.

Iris (Bulbous) (English, Spanish,
Dutch)

B LIGHT , Blossom. Botrytis cinerea; Glomerella
cingulata, MD.
B LIGHT , Leaf; Ink Disease of Bulbs.
Mystrosporium adustum, NC, OR, VA.
B LIGHT , Southern; White Bulb Rot. Sclerotium
rolfsii, CA, CT, FL, MD, NC, OR, SC, TX.
L EAF S POT , Blight. Didymellina macrospora,
CA, NC, TX, WA.
N EMATODE , Bulb. Ditylenchus dipsaci ( D. iridis ),
FL, NY, NC, OR, SC, VA, WA.
N EMATODE , Root Knot. Meloidogyne sp., NC.
N EMATODE , Root Plate. Aphelenchoides
parietinus, MI, NY, NC, TX, WA.
N ONPARASITIC . Blindness. Complex physiological
causes.
R OT , Basal. Fusarium oxysporum, AZ, CA, NY,
NC, OR, TX, VA, WA.
R OT , Black. Sclerotinia bulborum, bulb
rot, Northwest; Rhizoctonia tuliparum,
occasional; Blue Mold, Penicillium spp.,
general.
R OT , Root, Neck. Rhizoctonia solani, NJ, Pacific
Northwest.
R UST . Puccinia iridis (II, III), CA, IN, LA, NC.
V IRUS . Iris Mosaic, general; Iris Severe Mosaic.

Ironweed (Vernonia)

B LACK M ILDEW . Stigmella vernoniae, MO.
D OWNY M ILDEW . Plasmopara halstedii, KS, MO.
L EAF S POT . Cercospora noveboracensis, MO;
Ascochyta treleasei, WI; Mycosphaerella
sp.; Septoria sp., MO; C. oculata,WVto
AL, NE, TX, WI.
P OWDERY M ILDEW . Golovinomyces

Iris (Rhizomatous) (German, Siberian,
Native Species)

cichoracearum, general; Sphaerotheca

macularis,MO.
R OT , Root. Phymatotrichum omnivorum, TX.
R UST . Coleosporium vernoniae (I, III), general;
0, I on pine; Puccinia vernoniae (0, I, II, III),
widespread.

B ACTERIAL Soft Rot. Erwinia carotovora,
general.
B LIGHT , Blossom. Botrytis cinerea,MA.