Download Diseases of Roses

Diseases of Roses
John & Mitchie Moe
ARS Master Rosarians
Pacific Northwest District
Revised March 2015
May 25, 2012
This program is eligible for one CR Credit if pre-approved
by the District and National CR Chairs
An American Rose Society Presentation © 2015
Acknowledgements
• Most photos used in this program are copyrighted.
• Permission was received to use the copyrighted photos for
this educational program! Please do not copy or reproduce
for any other uses.
• An excellent source – the ARS Consulting Rosarian Manual
• Another excellent source - http://www.sactorose.org
Baldo’s Bugs & Roses, the website of Baldo Villegas,
known to rosarians as “The Bugman”
• Please – no commercial use of this program!
Introduction
• There are many diseases of roses that have described in various books,
but there are three that seem to afflict the rose garden at one time or
another:
• Mildew
• Blackspot
• Rust
• If these three can be controlled, the rose garden will be generally
disease free. They can often be managed by following these
recommendations:
• Buy certified stock free of diseases
• Keep free of weeds, fallen leaves, and disease-infested plants or canes
• Use regular spray programs, and practice good cultural methods
Note: This program deals primarily with identification of diseases, and does not get into specific
chemical controls, which is a subject by itself.
Powdery Mildew
Sphaerotheca pannosa
•
A very common disease of
roses – some roses more
susceptible than others!
•
Starts on leaves, but spreads
to buds and young shoots
•
Common in crowded plantings
where air circulation is poor
•
Optimum conditions for spore
germination are 71°F and 98
percent relative humidity
Jack Kelly Clark
Photo by Jack Kelly Clark
Warm days and cool nights makes any climate just right for this!
Powdery Mildew Control
•
Over-winters on infected
canes, spores move to new
leaves in spring to begin
disease cycle
•
Aggressive spring pruning will
remove a large source of this
fungus
•
Fungicides work best at onset
of disease, not after massive
infection has occurred
•
A regular fungicide spray
program is generally
necessary to prevent it
David Hughes, Gardenseeker.com
This is why the first fungicide spray is so important!
Black Spot
Diplocarpon rosae
Photo by Jack Kelly Clark
• One of the most
common diseases of
roses
• Disease cycle
typically begins on
canes and leaves
infected the previous
season
• Leaves less than two
weeks old are the
most susceptible
• Small 2 mm black spots enlarging to 12 mm with generally circular
appearance, but having a feathery edge found on the upper leaf
surfaces as well as immature canes
Blackspot (cont.)
•
Lower areas are more likely to be
infected as spores are splashed up
on new foliage during rains or
irrigation– will continue up the
stem - as disease spreads, leaves
go from green to yellow and then
drop
•
Becomes very active in a wet
environment with temps around
70°F – needs about 7 hours to
produce new spores to infect
additional leaves and canes within
a few days
Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org
Blackspot Control
•
Good sanitation will help –
remove diseased leaves
•
Spores can over winter on
canes, and the entire cycle will
repeat next year if a fungicide
spray program is not started
early and maintained!
•
Aggressive spring pruning will
remove a large source of fungus
•
Prune to allow air circulation,
and water without wetting the
foliage
•
Buy disease resistant varieties of
roses
Photo by Jack Kelly Clark
Rust
• A fungal disease common in
many areas, easily identified
•
Phragmidium spp
Appears on the underside of
the foliage as red-orange spots
• Thrives in cool, moist weather
• The summer stage is cyclic, and
may repeat every 10 to 14 days
in favorable weather
• Fungus overwinters on infected
leaves and canes
• Spores are wind borne
• Can defoliate the plant
Clair Martin
Rust Control
• Good sanitation will help
to prevent early season
infections
• Remove affected leaves
and dispose in trash
• Don’t water in the
evening so that the leaf
surface is wet over night
• Fungicide you use for
powdery mildew or black
spot is usually effective
Univ of GA
Downy Mildew
Peronospora sparsa
•
A very serious disease that can
affect all roses!
•
May appear when favorable
conditions of humidity over 85%
and temps of 65 - 75° F
•
Under cool and moist spring
conditions, young leaves, stems
and flowers may show purple to
red or brown irregular blotches
that tend to follow the leaf veins
•
Advanced infections will have
yellowing of leaves
Gail Trimble
Downy Mildew (cont.)
• White to grayish fungal
threads containing
spores coat the
undersides of leaves
• Spores may germinate
in as little as 4 hours,
and appear on leaf
surfaces in 3 days
• Can defoliate a plant in
a day or so
• Fungus can winter-over
as spores in or on plant
parts
Photo by Jack Kelly Clark
Treating Downy Mildew
• Once seen, it is generally
too late to prevent severe
leaf drop, which begins at
the top!
• Before treating, severely
prune heavily infected and
defoliated plants to
encourage new growth
• Destroy all cut material,
spores can live for a
month
• Treating generally requires
using some very potent
and costly fungicides
Gail Trimble
Anthracnose
Sphaceloma rosarum
• Initially spots are small and black easily confused with blackspot
• Spores believed to be carried by
water or rain to new leaves and
stems
• As disease progresses, spots
become purple to brown and
centers turn gray or white with
dark margin
• This light-colored center best
defines the difference with
blackspot
• Can be severe under cool, moist
spring conditions
Baldo Villegas
Anthracnose (cont.)
• Tissue may drop out of the
center of the spots, giving
infected leaves its other name
of “Shot Hole Fungus”
• Fungus overwinters as spores
mainly in old lesions on canes
• Can cause leaf drop that
weakens the plant
• In extreme cases, it can result
in complete defoliation
Gail Trimble
Anthracnose Control
• Sanitation is best means of
control – remove diseased
leaves, and dispose in trash
• Plant spacing, use of drip
lines or soaker hoses rather
than sprinklers should help
• Prune out canes that have
infections in fall – dispose
in trash, not in compost pile
• Fungicide used for black
spot is usually effective
Paul Bachi
Botrytis Blight
•
When the weather is cool and wet, the
Botrytis cinerea
conditions are right for this fungus
•
Most common symptom - young flower
buds droop, turn black at the base
•
Later produce
the cottony
grey-black
mycelium of
Gail Trimble
the fungus
Gail Trimble
• Can affect any part of the plant except roots
Botrytis Blight (cont.)
• Spores are moved to other plants
by wind or blowing rain
• Note the grayish fuzzy growth on
the cane that indicates botrytis
• Good ventilation is also essential
in reducing disease incidence
• Fungus may overwinter in dead
plant material
• Remove blighted flowers, leaves,
or entire plants if infected at the
base – discard in trash!
• Fungus becomes quickly
resistant, so alternate fungicides
Univ of GA
Rose Canker
• A fungal disease that can
affect any part of the
plant, but most common
on stems and canes
Coniothyrium spp
• After a cold wet winter,
pruned stems provide
wound sites for canker
causing fungi
• Canker can also enter
thru leaf scars – do NOT
tear off leaves during fall
pruning!
John Moe
Rose Canker (cont.)
• Tissue within the canker
begins to dry out and shrink,
giving it a shriveled look
• Stems will yellow, often have
red spots and later become a
dark brown or black
• Can be acute on old roses
that have lost vigor, and on
new bare root roses coming
from cold storage
John Moe
Rose Canker Control
• Time fall prune so tips can
callus before winter
• Dormant spray can protect
pruning cuts
• Disinfect pruners before
moving to another bush
• In spring, remove infected
canes and spray for fungal
disease
• Fungicides that control black
spot will also help to control
canker
John Moe
Bacterial Crown Gall
Agrobacterium tumefaciens
• Bacterial disease usually seen
on bud union, or on the trunk
• Thrives in warm, sunny
weather; not active in cold
weather
• Cork-like substance that will
turn brown and harden as it
ages
• Plants will usually be stunted
in their growth habits
John Moe
Bacterial Crown Gall (cont.)
• Can persist in the soil in a
dormant state for years
• The growth can be removed,
however, chances are it will
eventually return
• If you do cut out galls, use a
sharp knife or pruning shears,
brush on full strength bleach
• Destroy the galls; disinfect
cutting tools with Lysol® after
each cut
John Moe
This cut was most likely made with infected pruners!
Bacterial Crown Gall Control
• Avoid injury to canes and stems
when planting or cultivating
• Maintain good garden sanitation
and cultural practices
• If heavily infected, remove and
discard the plant
• If you can, replace soil where
rose was growing with new soil,
or saturate the soil well with a
10% bleach solution before
replanting
• Disease is un-treatable
Rose Mosaic
Prunus Necrotic Ringspot Virus
• Probably the most commonly
found virus in roses
• Mosaic is primarily
transmitted by propagation
• Usually appears in spring as a
distortion of growing tips and
leaves
• Symptoms include coloration
patterns (shown), distorted
leaf growth, slow to develop,
and fewer quality blooms
Univ of Georgia
Rose Mosaic (cont.)
• No cure – buy quality plants
showing no symptoms of
the disease
• Commercial rose growers
purchase rootstock that has
been “virus indexed”, which
means it has been lab tested
to confirm the absence of
the virus in the plants tissue
• Overall damage from the
disease may be mostly
cosmetic with some
reduction of plant vigor
Univ of GA
Jack Kelly Clark
Rose Rosette Disease (RRD)
• Exact cause unknown
• The distinctive red stems,
distorted and wrinkled
leaves are symptoms
• The main host is R. multiflora
• New growth appears
unusually soft and pliable
• RRD is suspected to be
carried from plant to plant
by the tiny eriophyid mite
• Can be confused with plant
damage from chemicals like
Roundup®
Photo by James W. Amrine Jr.
Rose Rosette Disease
• The stems grow
slowly and produce
excessive thorns
• There may be so
many thorns that
the stem may be
non-visible!
• Thorns are often
red-tinged
Photo by
John Hartman
Rose Rosette Disease
• If you are sure
that it is this
disease, you
need to act
fast!
• Very serious
disease – no
cure, fatal to
plant!
Photo by James W. Amrine Jr.
• Remove the diseased plant as soon as possible (including the
entire root system) and destroy it!
• Considered to be one of the most damaging problems of roses!
Questions?
Thank You
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