Diseases of Herbaceous Ornamentals Houseplants

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Fall 2007Specialized Master Gardener Training
Ornamental Disease Potpourri(27 Diseases You Can
Learn To Love)
Brian D. Hudelson Department of Plant
Pathology University of Wisconsin-Madison/Extensio
n
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Ornamental Disease PotpourriPowdery Mildews

• Cause
• Erysiphe spp. Microsphaera spp.
• Uncinula spp. Sphaerotheca spp.
• Phyllactinia spp. Podosphaera spp.
• Blumeria spp. Brasiliomyces spp.
• Sawadaea spp.
• Oidium spp. Ovulariopsis spp.
• Hosts
• Virtually everything

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Glen Stanosz, UW-Madison Plant Pathology
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Glen Stanosz, UW-Madison Plant Pathology
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Glen Stanosz, UW-Madison Plant Pathology
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Ornamental Disease PotpourriPowdery Mildews

• Control
• Remove diseased plant material and debris
• Reduce humidity
• Plant less densely
• Thin existing stands
• Use resistant cultivars/varieties

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Ornamental Disease PotpourriPowdery Mildews

• Control
• Use fungicides to prevent infections
• Dinocap, dithiocarbamates, myclobutanil,
  triadimefon, triforine, sulfur or
  thiophanate-methyl
• Baking soda (1.5 T/gal) and horticultural oil (3
  T/gal)
• Apply when humidity gt60-70
• 7-14 day application interval

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Ornamental Disease PotpourriAnthracnose

• Causes Gloeosporium spp. Collectotrichum
  spp. Other fungi
• Hosts
• Anything and everything
• Ash, maple, oak

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Ornamental Disease PotpourriAnthracnose

• Control
• DO NOT panic
• Remove diseased leaves
• Use fungicides to prevent infections
• Copper-containing fungicides, chlorothalonil,
  mancozeb, thiophanate methyl
• 3 appplications at bud break, 1/2 expansion of
  leaves, full leaf expansion

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Ornamental Disease PotpourriBlack Spot

• Pathogen Marssonina rosae
• Host Rose

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Ornamental Disease PotpourriBlack Spot

• Control
• Plant/produce resistant rose varieties
• Do not overcrowd rose plantings
• Do not overhead water
• Do not overwater
• Prune rose shrubs to remove diseased canes and
  open the plant canopy
• Remove and destroy infested leaf debris

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Ornamental Disease PotpourriBlack Spot

• Control
• Use fungicides to prevent infections
• Chlorothalonil, copper-containing fungicides,
  mancozeb, maneb, myclobutanil, propiconazole,
  thiophanate-methyl
• Baking soda (1.5 T/gal) and horticultural oil (3
  T/gal)
• Neem oil
• 7-14 day application interval

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Ornamental Disease Potpourri Scab

• Cause Venturia inaequalis
• Hosts
• Apple
• Crabapple
• Pear
• Mountain ash

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Ornamental Disease PotpourriScab

• Control
• Plant/produce resistant varieties
• Remove and destroy infested leaf debris
• Thin trees to promote air flow
• Use fungicides to prevent infections
• Captan, chlorothalonil, mancozeb, myclobutanil,
  propiconazole, thiophanate-methyl
• From bud break through the end of favorable
  weather
• Applications every 7-14 days

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Ornamental Disease PotpourriCedar-Apple Rust

• Cause Gymnosporangium spp.
• Hosts
• Junipers
• Rosaceous plants apple, crabapple, hawthorn,
  quince

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Ornamental Disease PotpourriCedar-Apple Rust

• Control
• Use resistant cultivars/varieties
• Remove galls
• Use fungicides to prevent infections
• Ferbam, triadimefon
• Mid May through mid June (rosaceous hosts)
• Early July through August (juniper hosts)
• 7-21 day application interval

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Ornamental Disease PotpourriRhizosphaera Needle
Cast

• Pathogen Rhizosphaera kalkhoffii
• Hosts (major)
• Colorado blue spruce
• Other spruces Engelmann, black, Serbian, Sitka
• Hosts (minor)
• Pines Austrian, mugo, eastern white pine
• Douglas fir, hemlock, balsam fir

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Stigmina Needle Cast
Mary Ann Hansen, Virginia Tech
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Ornamental Disease PotpourriRhizosphaera Needle
Cast

• Control
• DO NOT plant Colorado blue spruce
• Do not crowd trees when planting
• Thin branches to increase airflow
• Prevent tree stress
• Prune diseased branches

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Ornamental Disease PotpourriRhizosphaera Needle
Cast

• Control
• Use fungicides to prevent infections
• Copper-containing fungicides, chlorothalonil
• Bud break
• 3-4 week application interval under favorable
  conditions

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Ornamental Disease PotpourriDothistroma Needle
Blight

• Pathogen Dothistroma pini
• Hosts
• Austrian pine
• Mugo pine
• Ponderosa pine

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Ornamental Disease PotpourriDothistroma Needle
Blight

• Control
• Plant disease free trees
• Plant resistant varieties
• Remove fallen infected needles (?)
• Use fungicides to prevent infections
• Copper-containing fungicides
• Early June
• 1 applications, or 2 applications spaced 3-4
  weeks apart

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Ornamental Disease PotpourriXanthomonas Leaf
Diseases

• Cause Xanthomonas campestris
• - pv. poinsettiicola - pv. hederae
• - pv. begoniae - pv. dieffenbachiae
• - pv. pelargonii
• Hosts
• - Poinsettia - Ivies
• - Begonia - Dumbcane et al.
• - Geranium

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Ornamental Disease PotpourriXanthomonas Leaf
Diseases

• Control
• Start with clean propagation materials
• Follow strict sanitation procedures when working
  with plant materials
• Remove symptomatic plants
• Remove contaminated plant debris
• Disinfest greenhouses after production

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Ornamental Disease PotpourriFoliar Nematodes

• Cause Aphelenchoides spp.
• Hosts
• Wide host range
• Houseplants African violets, ferns,
  begonia chrysanthemum
• Landscape plants Hosta

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Ornamental Disease PotpourriFoliar Nematodes

• Control
• Start with clean propagation materials
• Follow strict sanitation procedures when working
  with plant materials
• Remove symptomatic plants
• Remove contaminated plant debris
• Avoid overhead irrigation
• Hot water treatments (120-140F for up to 10 min.)

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Ornamental Disease Potpourri Botrytis
Blight/Gray Mold

• Pathogen
• Botrytis cinerea
• Hosts
• Virtually everything (particularly flower parts)
• Hit list roses, peonies, geranium

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Ornamental Disease Potpourri Botrytis
Blight/Gray Mold

• Control
• Remove and destroy diseased plant material
• Remove senescing plant parts
• Plant less densely
• Thin existing plant stands
• Do not overhead watering
• Do not overwater

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Ornamental Disease PotpourriBotrytis Blight/Gray
Mold

• Control
• Use fungicides to prevent infections
• Chlorothalonil, copper-containing fungicides,
  fludioxonil, iprodione, mancozeb, maneb,
  thiophanate-methyl, triflumizole
• 7-14 day application interval
• Apply during periods of high moisture

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Ornamental Disease PotpourriBlack Knot

• Cause Apiosporina morbosa
• Hosts
• Prunus species
• Plums
• Cherries

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Ornamental Disease PotpourriBlack Knot

• Control
• Do not plant infected Prunus stock
• Buy black knot-resistant varieties if available
  (Prunus Accolade, Prunus sargentii, Prunus
  maackii)
• Remove volunteer plums/cherries
• Prune diseased branches
• Do not use fungicides

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Ornamental Disease PotpourriNectria Canker

• Pathogen Nectria spp.
• Hosts
• Many woody ornamentals
• Honey locust
• Maple

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Joseph OBrien, USDA Forest Service, Bugwood.org,
www.forestryimages.org
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Joseph OBrien, USDA Forest Service, Bugwood.org,
www.forestryimages.org
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Petr Kapitola, State Phytosanitary
Administration, Czechia, www.forestryimages.org
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Ornamental Disease PotpourriNectria Canker

• Control
• Choose well-adapted trees and shrubs
• Water and fertilize trees and shrubs properly
• Prune properly when maintenance pruning
• Reduce environmental stresses/injuries
• Prune out infected branches
• Disinfest tools between pruning cuts
• Do not use fungicides

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Ornamental Disease PotpourriGolden Canker

• Cause Cryptodiaporthe corni
• Host Pagoda dogwood

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Ornamental Disease PotpourriGolden Canker

• Control
• Prune diseased branches
• Reduce plant stress
• Consider tree placement
• Water adequately
• Mulch adequately
• Fertilizer appropriately
• Do not use fungicides for control

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Ornamental Disease PotpourriFire Blight

• Cause Erwinia amylovora
• Hosts
• Many rosaceous plants
• Apple, crabapple, pear, mountain ash, cotoneaster

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Ornamental Disease PotpourriFire Blight

• Control
• Plant resistant varieties where available
• Prune diseased branches
• Do not over-fertilize with nitrogen
• Use bactericides to prevent infections (?)
• Copper-containing fungicides, antibiotics
• During flowering
• Applications every 7-14 days (3-4 days)

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Ornamental Disease PotpourriRamorum Blight
(Sudden Oak Death)

• Cause Phytophthora ramorum
• Hosts
• General An increasingly expanding list of woody
  and herbaceous ornamentals. Check out
  nature.berkeley.edu/comtf for an up-to-date list
• Shrubs Rhododendron, lilac, witch-hazel,
  viburnum, (hybrid and rugosa roses), and many
  others

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Joseph O'Brien, USDA Forest Service
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Ken Peek, Alameda Dept. of Agriculture
Shane Sela, Canadian Food Inspection Agency
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Dr. Alexandra Schlenzig, Scottish Agricultural
Science Agency
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John Bienapfl
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Ornamental Disease PotpourriRamorum Blight
(Sudden Oak Death)

• Control
• Buy woody ornamentals from a reputable source
• Inspect plants prior to purchase for symptoms of
  sudden oak death
• Keep new plants isolated from established plants
• Contact the PDDC if you believe you have found
  this disease!
• Remove and destroy infected plants (under the
  guidance of WI DATCP and/or USDA APHIS)

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Ornamental Disease PotpourriCytospora Canker

• Pathogen Leucocytospora kunzei
• Hosts
• Colorado blue spruce
• Norway spruces
• Other spruces
• Douglas fir

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Ornamental Disease PotpourriCytospora Canker

• Control
• DO NOT plant Colorado blue spruce
• Do not crowd trees when planting
• Thin branches to increase airflow
• Prevent tree stress
• Prune diseased branches
• Do not use fungicides

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Ornamental Disease PotpourriDiplodia Tip Blight

• Pathogen Diplodia pinea (Sphaeropsis sapinea)
• Hosts (major)
• Pines Austrian
• Other pines red, jack, Scots, mugo
• Hosts (minor)
• Other conifers cedars, cypresses, firs,
  spruces, junipers, yews

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Ornamental Disease PotpourriDiplodia Tip Blight

• Control
• DO NOT plant Austrian pines
• Prevent tree stress, particularly water stress
• Thin branches to increase airflow
• Prune diseased branches
• Remove infected cones

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Ornamental Disease PotpourriDiplodia Tip Blight

• Control
• Use fungicides to prevent infections
• Thiophanate methyl, chlorothalonil
• Bud break through shoot elongation
• 14 day application interval

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Ornamental Disease PotpourriPhomopsis Tip
Blight/Canker

• Pathogen
• Phomopsis spp.
• Phomopsis juniperovora
• Hosts
• Most woody ornamentals
• Junipers

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Theodor D. Leininger, USDA Forest Service,
Bugwood.org, www.forestryimages.org
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Edward L. Barnard, FL Department of Agriculture
and Consumer Services, Bugwood.org,
www.forestryimages.org
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Ornamental Disease PotpourriPhomopsis Tip
Blight/Canker

• Control
• Use resistant varieties where available
• Do not crowd trees/shrubs when planting
• Prevent tree/shrub stress
• Avoid over-fertilization, particularly with
  nitrogen
• Prune diseased branches, but avoid excessive
  pruning
• Disinfest tools between pruning cuts

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Ornamental Disease PotpourriPhomopsis Tip
Blight/Canker

• Control
• Use fungicides to prevent infections on junipers
• mancozeb, copper-containing fungicides,
  thiophanate methyl
• Bud break through period of rapid growth
• 7-21 day application interval

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Ornamental Disease PotpourriDutch Elm Disease

• Causes Ophiostoma ulmi Ceratocystis
  ulmi Ophiostoma novo-ulmi (Pesotum ulmi
  Graphium ulmi)
• Hosts
• Highly susceptible elms
• American, Belgian, English, red, rock, September,
  European white, winged
• Elms of intermediate susceptibility
• Cedar, European field (smooth-leaf), wych (Scots)

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Ornamental Disease PotpourriDutch Elm Disease

• Transmission
• Elm bark beetles
• Scolytus multistriatus (European)
• Hylurgopinus rufipes (Native)
• Root grafts
• Major method of movementin clumps of elms
• Ophiostoma ulmi can reachthe roots during the
  firstseason of infection

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Ornamental Disease PotpourriDutch Elm Disease

• Control
• Remove diseased elms
• Disrupt root grafts
• Mechanically (vibratory plow or trenching
  machine)
• Chemically (soil fumigant)
• Physical barriers
• Be careful using elm wood
• Remove bark
• Cover wood

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Ornamental Disease PotpourriDutch Elm Disease

• Control
• Prune diseased branches
• Use fungicides injections
• Propiconazole, thiabendazole
• Prophylactic
• Every 12-24 months

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Ornamental Disease PotpourriDutch Elm Disease

• Control
• Plant resistant elms
• Crosses between American and other elms
• True American elms
• American Liberty
• Independence
• Princeton
• Valley Forge
• New Harmony

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Ornamental Disease PotpourriDutch Elm Disease

• Control
• Treatments of dubious use
• Tracing
• Verticillium dahliae

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Ornamental Disease PotpourriOak Wilt

• Cause Ceratocystis fagacearum (Chalara sp.)
• Hosts
• About 20 species of oak
• Black/red oak group northern red, northern pin,
  black
• White oak group white, bur, swamp white
• Chinese chestnut

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Ornamental Disease PotpourriOak Wilt

• Transmission
• Oak bark beetles
• Pseudopityophthorus ninutissimus
• Pseudopityophthorus pruinosus
• Sap beetles
• Carpophilus spp.
• Colopterus spp.
• Cryptarcha spp.
• Epuraea spp.
• Clischrochilus spp.

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Ornamental Disease PotpourriOak Wilt

• Transmission
• Root grafts
• Major method of movementin clumps of oaks
• Can form between treesin the same subgenus
• Black/red oak group
• White oak group
• Movement of up to 20-25 ft/year

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Ornamental Disease PotpourriOak Wilt

• Control
• Do not prune or wound oaks from bud break to 2-3
  weeks past full leaf development
• Disrupt root grafts
• Mechanically (vibratory plow or trenching
  machine)
• Chemically (soil fumigant)
• Physical barriers
• Remove diseased (and healthy) trees

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Ornamental Disease PotpourriOak Wilt

• Control
• Be careful using oak wood
• Remove bark
• Cover wood
• Use fungicide injections
• Propiconazole
• Prophylactic (or therapeutic)
• Every 12-24 months

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Ornamental Disease PotpourriVerticillium Wilt

• Causes Verticillium dahliae
  Verticillium albo-atrum
• Hosts
• Anything and everything
• Many woody ornamentals
• Many herbaceous plants
• New host Snowberry

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Ornamental Disease PotpourriVerticillium Wilt

• Control
• Avoid Verticillium-infested areas
• Pretest soils/mulches/composts for the presence
  of Verticillium
• Fumigate heavily infested soils
• Keep broad-leaf weeds under control
• Avoid municipal mulches

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• Wood Chips as an Inoculum Source
• Amur maple
• 30.0/25.0 (Trted)
• 0.0/0.0 (Non-Trted)
• Green Ash
• 23.7/10.5 (Trted)
• 0.0/0.0 (Non-Trted)
• Redbud
• 10.7/13.3 (Trted)
• 0.0/0.0 (Non-Trted)

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Ornamental Disease PotpourriVerticillium Wilt

• Control
• Use resistant plants
• CONIFERS Pines, spruces, firs, junipers
• DECIDUOUS TREES/SHRUBS Beech, birch, ginkgo,
  hackberry, hawthorn, hickory, honey locust,
  mountain ash, white oak, bur oak, poplar,
  serviceberry, sycamore, willow

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Ornamental Disease PotpourriVerticillium Wilt

• Control
• Prevent plant stress
• Prune diseased (wilted) areas
• Make infected trees comfortable until they die
• Remove diseased plants
• Destroy infected materials
• Composting?

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Ornamental Disease PotpourriBacterial
(Ralstonia) Wilt

• Cause Ralstonia solanacearum
• races
• biovars
• Hosts
• Geranium
• Potato
• Many other herbaceous plants

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Ornamental Disease PotpourriBacterial
(Ralstonia) Wilt

• Control
• Start with clean propagation materials
• Follow strict sanitation procedures when working
  with plant materials
• Keep plants from different sources separated
• Disinfect pruning tools
• Disinfect hands when working with plants
• Remove and destroy infected plants (under the
  guidance of WI DATCP and/or USDA APHIS)

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Ornamental Disease PotpourriDamping-Off/Seedling
Blights

• Pathogens
• Pythium spp.
• Rhizoctonia solani
• Fusarium spp.
• Hosts
• Seedlings of virtually anything

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Ornamental Disease PotpourriDamping-Off/Seedling
Blights

• Control
• Use a pasteurized soil mixture
• Use decontaminated pots, working surfaces and
  tools
• Moderate soil moisture
• Use a soil with adequate drainage
• Do not overwater

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Ornamental Disease PotpourriDamping-Off/Seedling
Blights

• Control
• Germinate seeds at higher temperatures
• Use fungicides to protect seedlings
• Etridiazole, metalaxyl, mefenoxam, captan
• Applied as a seed treatment or drench

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Ornamental Disease PotpourriRoot Rots

• Pathogens Pythium spp., Phytophthora spp.,
  Rhizoctonia solani, Fusarium spp.
  Thielviopsis spp.
• Hosts
• Virtually anything
• Firs
• Rhododendrons
• Peonies

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Ornamental Disease PotpourriRoot Rots

• Control
• Moderate soil moisture
• Plant outdoor plants in well-drained sites
• Use a soil with adequate drainage
• Improve drainage in poorly drained sites/soil
  mixes
• Add organic matter to improve drainage
• Use raised beds
• Do not overwater
• Mulch properly

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Ornamental Disease PotpourriRoot Rots

• Control
• Do not move contaminated soil or plants to
  non-infested areas
• Use fungicides to prevent infections
• Etridiazole, metalaxyl, mefenoxam, fosetyl-Al
• PCNB, thiophanate-methyl, fludioxonil
• Use granular formulations if possible
• Use during periods of wet weather

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Ornamental Disease PotpourriSouthern Blight

• Pathogen
• Sclerotium rolfsii
• Hosts
• Many herbaceous ornamentals
• Some woody ornamentals

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Ornamental Disease PotpourriSouthern Blight

• Control
• Inspect plants prior to purchase and avoid
  infected plants
• Remove infected plants
• Use fungicides for control
• Triadimefon, PCNB, fludioxonil
• 14 28 day intervals

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Ornamental Disease PotpourriPlum Pox

• Cause Plum pox virus
• Hosts
• Plum
• Peach
• Nectarines
• Apricot
• Ornamental Prunus spp.

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Ornamental Disease PotpourriPlum Pox

• Transmission
• Aphids
• Aphis craccivora Aphis spiraecola
• Brachycaudus helichrysi Brachycaudus
  cardui
• Myzus persicae Myzus varians
• Myzus (Phorodon) humuli
• Mechanical
• Grafting
• Seed (apricot)

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Biologische Bundesanstalt für Land und
Forstwirtschaft
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Biologische Bundesanstalt für Land und
Forstwirtschaft
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Ornamental Disease PotpourriPlum Pox

• Control
• Buy woody ornamentals from a reputable source
• Inspect Prunus spp. prior to purchase for
  symptoms of plum pox
• Keep new trees isolated from established trees
• Contact the PDDC if you believe you have found
  this disease!
• Remove and destroy infected plants (under the
  guidance of WI DATCP and/or USDA APHIS)

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Ornamental Disease PotpourriAster Yellows

• Pathogen
• Aster yellows phytoplasma
• Hosts
• Many plants in the Asteraceae
• Many other plants in many other plant families

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Ornamental Disease PotpourriAster Yellows

• Control
• Remove infected plants
• Control leafhopper vector (?)

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Ornamental Disease PotpourriWhere to Go for Help
Plant Disease Diagnostics Clinic Department of
Plant Pathology University of Wisconsin-Madison 16
30 Linden Drive Madison, WI 53706-1598 (608)
262-2863 bdh_at_plantpath.wisc.edu http//pddc.wisc.e
du