Host Plants - Westcott's Plant Disease - page 621

R UST . Phragmidium americanum (0, I, II, III),
on leaves of cultivated and native roses, ME to
NC, ND, TX; P. montivagum (0, I, II, III), on
native species, SD to NM, AZ, WA;
P. mucronatum ( P. disciflorum ), the common
rust of cultivated roses, possibly on native
species (0, I), on leaves and stems; II, III on
leaves, eastern states to Rocky Mts.; Pacific
Coast; P. fusiforme ( P. rosae-acicularis ) (0, I,
II, III), on native species, MI to CO, CA, WY;
P. rosae-californicae (0, I, II, III), on natives,
AZ, CA, MT, OR; P. rosae-pimpinellifoliae
( P. subcorticium ) (0, I), on stems; II, III on
leaves of brier and sweetbrier groups, northern
U.S.; P. rosicola (III), CO, MT, NE, on native
spp.; P. speciosum (0, I), on leaves and stems,
III on stems of cultivated and native roses,
general except far South.
S POT A NTHRACNOSE . Elsino¨ rosarum, ME to FL,
KS, MI, MO, TX; Pacific Coast.
U NKNOWN . Speckle. Chlorotic flecks in leaves,
not transmitted by grafting, MD, NJ, NY,
PA, TX, VA.
V IRUS . Rose Mosaic (in part Prunus Necrotic
Ring Spot and Apple Mosaic), Pacific Coast
and eastern states in greenhouses and in gar-
dens on plants shipped from the West Coast;
Rose Rosette (Witches' Broom), CA, KS,
MD, MO, OR; Rose Streak, MD, NJ, NY,
TX, VA; Rose Yellow Mosaic, CA, IL, MD,
NY, PA, VA; Crinkle. On Manetti
understock, sometimes garden roses, Pacific
Coast, MD, NY, PA, TX, VA; Rose Leaf
Curl, CA; Rose Spring Dwarf, CA.
W ILT . Verticillium albo-atrum, AR, CA, IL, NJ,
NY; probably wide spread.
Blackspot, brown canker, powdery mildew, and
rust are the big four diseases of garden roses.
Blackspot is almost inevitable except in some dry
western states, and shows up even there when over-
head watering is substituted for the usual irrigation.
It can be controlled by regular weekly spraying or
dusting. Powdery mildew, a problem on the Pacific
Coast, is increasing in eastern gardens. Brown can-
ker and other cane diseases are best controlled at
spring pruning, by cutting out infected canes and
cutting other canes just above a bud, not leaving
any stub to die back. Cankers are increased by

excessive winter protection. Where temperatures
permit, as in the Central Atlantic region, eliminate
soil mounding and other special winter treatment.
Roses are sensitive to many chemicals; it is
important to distinguish spray injury from
blackspot and not increase the dosage because
you think you are not getting control. Combination
sprays or dusts should take care of most diseases,
as well as insects, in one operation. The bacterial
crown gall is occasionally present on plants pur-
chased from a nursery. Ask for a replacement; do
not contaminate your soil by planting such a bush.

Rose - Acacia (Robinia hispida)

L EAF S POT . Alternaria fasciculata, ND.
R OT , Root. Phymatotrichum omnivorum, TX.

Roselle (Hibiscus sabdariffa)

A NTHRACNOSE , Pod Spot. Colletotrichum

gloeosporioides, FL.
B LIGHT , Gray Mold. Botrytis cinerea,MD.
B LIGHT , Southern. Sclerotium rolfsii, TX.
L EAF S POT . Cercospora hibisci, TX.
N EMATODE , Root Knot. Meloidogyne sp., TX.
P OWDERY M ILDEW . Microsphaera euphorbiae,
AL, FL.
R OT , Fruit, Stem. Fusarium sp., FL;

Phytophthora parasitica, TX.
R OT , Root. Phymatotrichum omnivorum, TX;
Rhizoctonia solani, TX.
W ILT . Fusarium oxysporum, FL.

Rose-Gentian (Sabatia)

A NTHRACNOSE . Gloeosporium sp., OK.
L EAF S POT . Cercospora sabbatiae, DE, MS, NC,
OK, TX.

Rose - Mallow (Hibiscus palustris)

B ACTERIAL Crown Gall. Agrobacterium

tumefaciens, MS.