SCOUTING FOR PLANT DISEASES Jean Williams-Woodward University of Georgia.
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Transcript of SCOUTING FOR PLANT DISEASES Jean Williams-Woodward University of Georgia.
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SCOUTING FOR PLANT DISEASES
Jean Williams-Woodward
University of Georgia
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Scouting for Plant Disease
• Disease control relies on prevention• You cannot cure a plant of a plant disease• You cannot manage diseases by reacting to symptoms
• The time between infection and symptom development may be 21 days or more
• By the time you see symptoms, it is too late to manage the disease on that plant
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Diseases come from…
• Infected plant liners, plugs, divisions• Off-shore production introducing exotic pathogens
into USA• Example: Daylily rust
• Residual plants from previous crop or previous season
• Plant and soil residues and debris
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Pathogens causing disease:
• Fungi • Root rots, leaf spots, rusts, mildews
• Bacteria• Leaf spots, vascular wilts, soft rots
• Viruses• Nematodes
• mostly foliar nematode
• Phytoplasmas• Aster yellows
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Disease Triangle
WATER! (wet foliage or soils, high humidity, poor air circulation)
Stressed or injured plant
Capable of causing disease (many are host specific)
Host Pathogen
Environment
Disease
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Disease Management Principles
• Eliminate initial inoculum (pathogen survival)• Sanitation• Scouting for early detection
• Reduce pathogen spread• Water splash• Plant-to-plant contact• Wind dispersal• Vectors (insects, workers, tools)
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Products available• Fungicides
• Primary disease management tool
• Bactericides• Coppers• Phosphonates (Xanthomonas sp.)
• Biological products• RootShield (Trichoderma harzianum)• Cease (Bacillus subtilis)
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Use Fungicides to Increase Lag Phase of Epidemic
0
20
40
60
80
100
120
No fungicideSpray #1Spray #2Spray #3Spray #4
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What to look for…• Concentrate on entryways into greenhouse (doors, open vents, walkways)
• Concentrate on incoming plants• Look for out-of-the-ordinary plants
• Stunted• Off-color• Yellowing• Wilting• Browning• Distorted• Leaf spotting
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Root and Cutting Diseases• Common diseases are damping-off and root rot• Symptoms include wilting, leaf yellowing, plant stunting,
softening and discoloration of roots, plant death• Major pathogens: Pythium, Phytophthora, Rhizoctonia• Disease favored by wet rooting medium, high humidity,
poor ventilation, high soluble salts (EC)
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Root Disease Symptoms
• Wilting, stunting, leaf yellowing and drop, softening and discoloration of roots and stems, branch dieback, plant deathPythiumPythium
RhizoctoniaRhizoctonia
PhytophthorPhytophthoraa
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Black Root Rot (Thielaviopsis basicola)
• Disease favored by:• High potting medium
moisture, alkaline medium pH, excess fertilization
• Spread • Water movement and
contaminated pots, trays, rooting medium
• Survives as chlamydospores• Control
• Sanitation, fungicides
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Botrytis Blight (Gray Mold)
• Spores dispersed by water impact and twisting from stalks upon drying
• Disease favored by • High humidity (>85%)• Moderate temperatures• Free moisture (4 hr at 79F)• Low light
• Control• Heating and venting,
sanitation, reduce plant wetness, fungicide sprays
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Fungal leaf spot diseases • Wet leaves favor disease• Remove infected leaves, plants• Fungicides used preventively and to reduce spread
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Leaf Rusts• Disease favored by:
• High humidity• Moderate to cool
temperatures• Spread by wind-blown
spores• Survives in living plants,
plant debris• Control
• Sanitation, discard plants, remove infected foliage
• Fungicides• Resistant cultivars
Daylily RustDaylily Rust
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Snapgradon RustSnapgradon Rust Geranium RustGeranium Rust
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Powdery mildew
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Powdery Mildew Downy Mildew
• Cool, humid, wet• Sporulates on underside
• Local and systemic
• Warm, humid, dry• Sporulates anywhere
• Local infections
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RoseRose ImpatiensImpatiens
LamiumLamium RudbeckiaRudbeckia
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VeronicaVeronica
ArgyranthemumArgyranthemum
From U. Mass website
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Bacterial Leaf Spots
• Disease favored by:• Free moisture on plant• Warmer temperatures• High humidity
• Spread• Water splashing• Plant-to-plant contact
• Survives in plant debris• Control
• Reduce water-splashing, sanitation!• Copper fungicides to reduce spread (limited)
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Virus DiseasesTSWV, INSV, CMV, TMV, others
• Common symptoms• Tissue deformation• Stunting• Leaf necrosis• Mottling, Mosaic• Ring spots