Diseases of Herbaceous Ornamentals Houseplants

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Specialized Master Gardener Training Diseases
of Ornamentals
Brian D. Hudelson Department of Plant
Pathology University of Wisconsin-Madison/Extensio
n
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Diseases of OrnamentalsDamping-Off/Seedling
Blights

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

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Diseases of OrnamentalsDamping-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
• Dont overwater

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Diseases of OrnamentalsDamping-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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Diseases of OrnamentalsRoot Rots

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

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Diseases of OrnamentalsRoot 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
• Dont overwater
• Mulch properly

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Diseases of OrnamentalsRoot Rots

• Control
• Dont move contaminated soil or plants to
  non-infested areas
• Pretest soils/mulches/composts for the presence
  of root rot fungi
• Decontaminate recycled water
• Filtration
• Irradiation
• Chemical treatment

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Diseases of OrnamentalsRoot Rots

• Control
• 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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Diseases of Ornamentals Fungal Leaf Spots/Blights

• Pathogens
• Many different fungi
• Alternaria spp., Cercospora spp., Phyllosticta
  spp., Colletotrichum spp., Drechslera spp,
  Bipolaris spp., Helminthosporium spp., Fusarium
  spp., ad nauseum
• Host
• Anything and everything

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Diseases of Ornamentals Fungal Leaf Spots/Blights

• Control
• Do not overhead water
• Do not overwater
• Do not overcrowd plants
• Remove and destroy infected leaves
• Remove and destroy infested leaf debris

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Diseases of Ornamentals Fungal Leaf Spots/Blights

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

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Diseases of OrnamentalsPowdery Mildews

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

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Diseases of OrnamentalsPowdery Mildews

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

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Diseases of OrnamentalsPowdery 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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Diseases of Ornamentals Botrytis Blight/Gray Mold

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

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Diseases of Ornamentals 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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Diseases of OrnamentalsBotrytis 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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Diseases of OrnamentalsSouthern Blight

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

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Diseases of OrnamentalsSouthern Blight

• Control
• Inspect plants prior to purchase and avoid
  infected plants
• Remove infected plants
• Use fungicides for control
• Bayleton
• 14 28 day intervals

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Diseases of OrnamentalsXanthomonas 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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Diseases of OrnamentalsXanthomonas 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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Diseases of OrnamentalsBacterial (Ralstonia) Wilt

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

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Diseases of OrnamentalsBacterial (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

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Diseases of OrnamentalsBacterial (Ralstonia) Wilt

• Control
• If you suspect you have the disease, contact the
  WI DATCP
• Remove symptomatic plants
• Remove co-mingled plants
• Remove contaminated plant debris
• Disinfest greenhouses after production

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Diseases of OrnamentalsHosta Virus X

• Cause Hosta virus X virus
• Host Hosta
• Gold Edger
• Gold Standard
• Golden Tiara
• Striptease
• Sum and Substance

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Diseases of OrnamentalsHosta Virus X

• Transmission Mechanical
• Pruning tools
• String edgers
• Shovels
• Touch

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hostalibrary.org/firstlook/HVX.htm
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hostalibrary.org/firstlook/HVX.htm
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Diseases of OrnamentalsHosta Virus X

• Control
• Buy Hosta plants from reputable sources
• Inspect hostas prior to purchase for symptoms of
  Hosta virus X
• Request that plants be tested for Hosta virus X
  prior to purchase
• Keep new Hosta plants isolated from established
  Hosta plants

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Diseases of OrnamentalsHosta Virus X

• Control
• Remove and destroy infected plants
• Remove infested plant debris
• Disinfest tools (and other items) that come into
  contact with potentially infected plants
• Sodium dodecyl sulfate (sodium lauryl sulfate)
  Alconox (1 1)
• Trisodium phosphate
• Alcohol dip followed by flaming

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Diseases of OrnamentalsTobacco Rattle

• Cause Tobacco Rattle Virus
• Hosts
• Ornamentals
• Astilbe, bleeding heart, columbine, coral bells,
  daffodils, epimedium, gladiolus, hyacinth,
  marigold, peony, tulip, vinca
• Vegetables
• Beans, beet, pepper, potato, spinach

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Diseases of OrnamentalsTobacco Rattle

• Transmission Stubby-root nematodes
• Trichodorus
• Paratrichodorus

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Anette Phibbs, WI DATCP
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Anette Phibbs, WI DATCP
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Diseases of Ornamentals Tobacco Rattle

• Control
• DO NOT buy symptomatic plants
• Grow non-susceptible plants
• Annual phlox, carnation, devils trumpet (downy
  thorn-apple), sweet William, zinnia, zombie
  cucumber
• Remove and destroy infected plants

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Diseases of Ornamentals Tobacco Rattle

• Control
• Disinfest tools (and other items) that come into
  contact with infected plants (e.g., when dividing
  plants)
• Sodium dodecyl sulfate (sodium lauryl sulfate)
  Alconox (1 1)
• Trisodium phosphate
• Alcohol dip followed by flaming
• Control of stubby-root nematode is not practical

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Diseases of OrnamentalsRoot Knot Nematodes

• Cause Meloidogyne spp.
• Hosts
• Wide host range

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Diseases of OrnamentalsRoot Knot Nematodes

• Control
• Use resistant varieties
• Plant non-hosts in infested areas
• Start with clean materials
• Use soil-less growing media or pasteurized soil
• Discard infected plants

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Diseases of OrnamentalsCyst Nematodes

• Cause Cactodera spp. (Cactus cyst nematode)
• Hosts
• Cacti
• Other succulents

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Diseases of OrnamentalsCyst Nematodes

• Control
• Start with clean materials
• Use soil-less growing media or pasteurized soil
• Discard infected plants

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Diseases of OrnamentalsFoliar Nematodes

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

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Diseases of OrnamentalsFoliar 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 (?)

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Diseases of OrnamentalsAster Yellows

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

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Diseases of OrnamentalsAster Yellows

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

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Diseases of OrnamentalsNutrient Abnormalities

• Cause
• Nutrient deficiencies
• Nutrient toxicities
• Affected plants
• Virtually anything

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Diseases of OrnamentalsNutrient Abnormalities

• Management
• Fertilize properly
• Water properly
• Maintain proper soil pH
• Repot plants on a regular basis
• Pot plants into inert containers

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Diseases of OrnamentalsPesticide Exposure

• Cause
• Accidental exposure to herbicides
• 2,4-D
• Dicamba
• Improper use of fungicides/bactericides/insecticid
  es
• Affected plants
• Virtually anything

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Diseases of OrnamentalsPesticide Exposure

• Control
• Apply herbicides only when needed
• Follow application directions exactly
• Apply herbicides only when wind speed is low (lt 5
  mph)
• Dont apply herbicides too close to nontarget
  plants
• Apply herbicides at low pressure
• Use amine rather than ester forms of herbicides

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Diseases of OrnamentalsEnvironmental Pollutants

• Cause Toxic compounds in the environment
• Fluoride
• Sulfur dioxide
• Ethylene
• Affected plants
• Virtually anything

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Diseases of OrnamentalsEnvironmental Pollutants

• Management
• Remove the source of the pollutant
• Avoid use of contaminated water
• Increase ventilation
• Make sure heating systems are working properly

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Diseases of OrnamentalsAdverse Environmental
Conditions

• Cause
• Temperature stress
• Water stress
• Light stress
• Affected plants
• Virtually anything

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Diseases of OrnamentalsAdverse Environmental
Conditions

• Management
• Maintain plants at proper temperatures
• Water plants appropriately
• Grow plants in appropriate light
• Avoid extreme changes in environmental factors

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Plant DiseasesWhere 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
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Plant DiseasesWhere to Go for Help
Soil and Plant Analysis Laboratory 8452 Mineral
Point Road Verona, WI 53593 (608)
262-4364 http//uwlab.soils.wisc.edu