1. An Introduction to Greenhouse Diseases Dr. Jean L. Williams-Woodward University of Georgia

2. Plant Disease Triangle HostPathogen Environment Disease

3. Disease Management 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)

4. Impossible Situations

5. Sanitation, Sanitation, Sanitation “Pet” plants Weeds – inside and out Dirt on floors, benches, pots, bamboo stakes, labels, etc. Worker clothes, hands, shoes, tools Hang water hoses

6. Root Rot Diseases Disease favored by wet potting medium, high humidity, poor ventilation, high soluble salts (EC) Disease spread by soil, insects, water splashing, plants Fungi survive in plant and soil debris

7. Pythium (and Phytophthora) Requires wet conditions Spread in water, soil Control by avoiding over watering, sanitation, fungicide drenches

8. Rhizoctonia Warmer temperatures and high humidity required Spread by hyphae (plant or soil contact), used pots, water-splash of soil Control by reducing humidity, sanitation, fungicide “sprenches”

9. Signs of wet environments Presence of fungus gnats and shore flies –Insects can spread root rotting pathogens Algae growth on pots, soil, benches, etc.

10. Black Root Rot Caused by fungus, Thielaviopsis basicola Disease favored by: –High potting medium moisture –Warmer temperatures –Alkaline medium pH –Excess fertilization Spread –Infected plants, water splash or movement, contaminated pots, trays, rooting medium

11. Black root rot Survival as chlamydospores (resting spores) –Within infected plants, soil debris on benches, stakes, pots Control –Acidify rooting medium pH, sanitation (clean pots, trays, benches, medium), cool root zone, fungicide drenches

12. Botrytis Blight Fungus readily produces spores on senescent tissues at 85% humidity

13. Botrytis Blight (Gray Mold) Spores are 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. Ventilation Problems

15. Powdery Mildew Disease is favored by: –High humidity (85% RH) –High fertility –Poor ventilation Spread –Air dispersed spores Survival –Plant debris Control –Reduce humidity, increase air circulation, fungicides

16. Bacterial Leaf Spots Disease favored by: –Warmer temperatures –Free moisture on plant –High humidity –Poor ventilation Spread –Water splashing –Plant to plant contact Survival –Plant debris Preventive Control –Copper fungicides

17. Leaf rusts Diseases favored by: –High humidity –Moderate to cool temperatures Spread by air and water dispersed spores. Survives in plant debris Control –Reduce humidity, sanitation, fungicides –Raise temperature to above 90-93F

18. Bacterial blight (Xanthomonas) Plants wilt, leaves yellow often in V-pattern Leaves have dark, sunken, greasy spots