1. Scouting for Plant Diseases
Jean Williams-Woodward
University of Georgia

2. 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

3. 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

4. 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

5. (wet foliage or soils, high humidity, poor air circulation)
Disease Triangle
Host
Pathogen
Stressed or injured plant
Capable of causing disease (many are host specific)
Disease
Environment
WATER!
(wet foliage or soils, high humidity, poor air circulation)

6. 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)

7. Products available Fungicides Bactericides Biological products
Primary disease management tool
Bactericides
Coppers
Phosphonates (Xanthomonas sp.)
Biological products
RootShield (Trichoderma harzianum)
Cease (Bacillus subtilis)

8. Use Fungicides to Increase Lag Phase of Epidemic

9. 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

10. 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)

11. Root Disease Symptoms
Wilting, stunting, leaf yellowing and drop, softening and discoloration of roots and stems, branch dieback, plant death
Phytophthora
Pythium
Rhizoctonia

12. 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

13. 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

14. Fungal leaf spot diseases
Wet leaves favor disease
Remove infected leaves, plants
Fungicides used preventively and to reduce spread

15. 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 Rust

16. Snapgradon Rust
Geranium Rust

17. Powdery mildew

18. Powdery Mildew Downy Mildew
Warm, humid, dry
Sporulates anywhere
Local infections
Cool, humid, wet
Sporulates on underside
Local and systemic

19. Rose
Impatiens
Lamium
Rudbeckia

20. Argyranthemum
Veronica
From U. Mass website

21. Bacterial Leaf Spots Disease favored by: Spread
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)

22. Virus Diseases TSWV, INSV, CMV, TMV, others
Common symptoms
Tissue deformation
Stunting
Leaf necrosis
Mottling, Mosaic
Ring spots