With continued moisture and high humidity in many areas of Manitoba
this year conditions have been ideal for rose (Rosa spp.) rust. (Phragmidium
spp.
 ) Already this year,
new growth has been infected by the fungus. Unlike many rusts which
have an alternate host, the fungus can complete it’s entire life
cycle (see picture) on the rose plant, and the
fungus can survive overwinter in Manitoba. |
 |
Symptoms:
|
 |
| Symptoms first show up in spring on the undersides of leaves and
other green parts of the plants including stems (see pictures),
initially the symptoms may be difficult to spot. The first signs of
the disease are masses of bright orange pustules (aeciospores). With
continued development, yellow to orange spots become noticeable on
the upper leaf surface (see picture). As the
severity of the disease increases, stem tissues and sepals may
become diseased and disfigured (see picture). |
 |
| There is a wide range of responses to infections by the various
rose cultivars (see the tables below for responses of selected
cultivars to rust), loss of leaves may not occur with an abundance
of pustules on some cultivars, whereas others will lose their leaves
with one pustule on a leaflet. |
 |
| The summer uredial stage has reddish orange pustules (see
pictures and may repeat every 10-14 days under favorable
environmental conditions (generally about 18-21°C with continuous
moisture on the plant surfaces of 2-4 hours—conditions commonly
associated with spring in Manitoba). The repeating summer uredial
stage is followed by wilting and defoliation of susceptible
cultivars. Generally summers in Manitoba are quite dry and hot, and
not suitable for further spread of the fungus. In Manitoba, the
black telia stage pustules are formed toward the end of autumn on
leaves and canes and initiate new
disease in the spring. |
 |
Management
During the season, removal of all diseased leaves during the
season and all remaining foliage during winter in conjunction with
spring pruning before new leaves appear helps to reduce the amount
of the fungus present and prevent early spring rust outbreaks.
Spring pruning of old canes will help to eliminate rust (present as
hardened telia) carry over on canes.
Any method of preventing condensation in greenhouses will aid in
controlling rust, as this will lessen the likelihood of free
moisture development on plant surfaces necessary for infection.
Prior to planting consider avoiding placing susceptible roses in
damp, shaded locations, which will be conducive for rust
development.
Preventative fungicidal sprays should be applied every seven days
during periods when environmental conditions favour disease
development. Currently foor commercial use: Products with the active
ingredient myclobutanil are registered. For domestic (home) use
there are a number of products (all of which are various
formulations of sulfur) that may be used. These products are also
effective for black spot and powdery mildew.
Tables of rose cultivar resistance (for black spot, powdery
mildew and rust)
| Disease Reaction: |
R = Resistant, little or no disease
M (Intermed. in older references) = moderate disease, some
resistance.
S = Susceptible, severe disease. |
| Grandiflora |
Black Spot |
Powdery Mildew |
Rust |
| Aquarius |
M |
M |
M |
| Camelot |
M |
M |
M |
| Comanche |
R |
S |
Intermed. |
| Gold Medal |
M |
M |
M |
| Love |
R |
R |
R |
| Montezuma |
R |
S |
S |
| New Year |
R |
M |
R |
| Pink Parfait |
Intermed. |
Intermed. |
Intermed. |
| Prominent |
M |
M |
R |
| Queen Elizabeth |
M* |
M |
M |
| Scarlet Knight |
Intermed. |
Intermed. |
Intermed. |
| Shreveport |
M* |
M |
M |
| Tournament of Roses |
R* |
R |
R |
| Hybrid Tea |
Black Spot |
Powdery Mildew |
Rust |
| Aztec |
R |
R |
Intermed. |
| Blue Nile |
M. |
M |
R |
| Bewitched |
R* |
R |
S |
| Bob Hope |
R |
Intermed. |
R |
| Charlotte |
R |
Intermed. |
Intermed. |
| Chicago Peace |
M |
M |
M |
| Chrysler Imperial |
R* |
S |
S |
| Color Magic |
M |
M |
M |
| Command Perfomance |
R |
S |
R |
| Dainty Bess |
M |
M |
M |
| Double Delight |
M* |
M |
M |
| Eclipse |
? |
S |
R |
| Electron |
R |
R |
R |
| Ena Harkness |
R |
S |
S |
| Folklore |
M |
M |
M |
| Fragrant Cloud |
M* |
M |
R to M |
| Garden Party |
R |
Intermed. |
R |
| Granada |
M |
S |
M |
| Headliner |
M |
S |
M |
| Heirloom |
M |
M |
M |
| Helen Traubel |
R |
Intermed. |
Intermed. |
| Helmut Schmidt |
R |
M |
R |
| Honor |
M |
M |
M |
| Irish Gold |
M |
M |
M |
| Just Joey |
R |
R |
R |
| Keepsake |
R |
R |
R |
| Kordes Perfecta |
R |
R |
S |
| Las Vegas |
R |
R |
R |
| Medallion |
M* |
M |
M |
| Miss All American Beauty |
R |
R |
S |
| Mister Lincoln |
M* |
M |
M |
| Mojave |
Intermed. |
Intermed. |
Intermed. |
| New Day |
R* |
M |
R |
| Olympiad |
M |
M |
R |
| Paradise |
M* |
M |
M |
| Pascali |
M |
M |
R |
| Peace |
M* |
Intermed. |
S to M |
| Peter Frankenfeld |
R |
M |
R |
| Pink Peace |
R |
Intermed. |
S |
| Polarstern |
R |
M |
R |
| Precious Platinum |
R |
M |
R |
| Princess Margaret |
M |
M |
R |
| Pristine |
M |
M |
R |
| Red Devil |
M |
M |
R |
| Royal Higness |
Intermed. |
S |
S |
| Silver Jubilee |
R |
R |
R |
| Tiffany |
M |
M |
M |
| Touch of Class |
M |
S |
R |
| Tropicana |
R* |
S |
R |
| Voodoo |
R |
R |
R |
| Floribunda |
Black Spot |
Powdery Mildew |
Rust |
| Bonica |
R* |
M |
R |
| Cherish |
M |
M |
E |
| Class Act |
M |
R |
R |
| Escapade |
R |
M |
M |
| Europeana |
R* |
R |
R |
| Eye Paint |
M |
R |
R |
| French Lace |
M |
M |
M |
| Iceberg |
R |
M |
R |
| Impatient |
R* |
R |
R |
| Intrigue |
M |
M |
R |
| Little Darling |
M |
M |
M |
| Liverpool Echo |
R |
R |
R |
| Marina |
M |
M |
R |
| Matangi |
R |
R |
R |
| Orangeade |
R |
M |
M |
| PlayGirl |
R |
R |
R |
| Playboy |
R |
R |
R |
| Redgold |
R |
M |
R |
| Regensberg |
R* |
R |
R |
| Sarabande |
R |
R |
R |
| Sexy Rexy |
R* |
R |
R |
| Shocking Blue |
M |
M |
M |
| Showbiz |
R |
R |
R |
| Sun Flare |
M |
M |
R |
| Sunsprite |
M |
M |
M |
| Trumpeter |
R* |
R |
R |
| Viva |
R |
R |
R |
| Shrub |
Black Sport |
Powdery Mildew |
Rust |
| Adelaide |
S |
R |
- |
| Champlain |
S |
Intermed. |
- |
| Charles Albanel |
R |
R |
- |
| Cuthbert Grant |
R |
R |
Intermed. |
| David Thompson |
R |
R |
- |
| Henry Hudson |
R |
R |
- |
| Henry Kelsey |
S |
R |
- |
| Jens Munk |
R |
R |
- |
| John Cabot |
Intermed. |
Intermed. |
- |
| John Franklin |
Intermed. |
Intermed. |
- |
| Martin Frobisher |
R |
R |
- |
| Prairie Princess |
Intermed. |
- |
R |
| William Baffin |
R |
R |
- |
| Climbers |
Black Spot |
Powdery Mildew |
Rust |
| Altissimo |
M |
M |
R |
| Dortmund |
R |
R |
R |
| Dublin Bay |
R |
R |
R |
| Golden Showers |
M |
M |
M |
| Handel |
M |
M |
R |
| Joseph's Coat |
M |
M |
M |
| Royal Sunset |
R |
R |
R |
References:
Colbaugh, P.F. et al. 2005. Rose variety reaction to blackspot
disease under minimal input growing conditions, 2001. Biological and
Cultural Tests for Control of Plant Diseases (online). Report 20:
O0018. DOI: 10.1094/BC20
Holcomb, G.E and T. Raiford. 2005. Reaction of rose cultivars to
blackspot disease, 2004. Biological and Cultural Tests for Control
of Plant Diseases (online). Report 20: O005. DOI: 10.1094/BC20
Horst, R.K. and Cloyd, R.A. 1981. Compendium of Rose Diseases.
American Phytopathological Society Press. Pilot Knob 88pp.
Western Committee on Plant Disease. Ornamentals Chapter.
http://www.westernforum.org
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