1. GREENHOUSE SANITATION Jean Williams-Woodward Extension Plant Pathologist UGA

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

3. Plant diseases are caused by… Fungi Bacteria Viruses Nematodes Phytoplasmas Aster Yellows 80% 10% 5%

4. Pathogens are spread by… Foliar pathogens: Water Wind Insects Grafting Pruning/pinching Vegetative propagation Seed Worker activity Soilborne pathogens: Soil Water Insects Plants Seed Worker activity

5. 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

6. 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

7. Diseases may be overlooked…

8. Look more closely…

9. Closer… Notice the defoliation, leaf spotting

10. Downy mildew on Knockout Rose

11. Turn leaf over and look for sporulation

12. Botrytis blight

13. Signs of wet environments Presence of fungus gnats and shore flies indicate high soil moisture Insects can spread root rot pathogens Algae growth on pots, soil, benches, etc. indicates high moisture environment

14. Root disease Plant wilting, off-color, etc. Pythium, Phytophthora, Rhizoctonia, Thielaviopsis

15. Damping off (both pre- and post-emergence)

16. Root death, sloughing, discoloration – WET substrate

17. Graded, gravel beds or ground-cloth covered gravel can reduce root disease incidence

18. Phytophthora and Pythium are water-molds Require water to spread and infect. Puddles saturate the rooting medium, as well as channel Phytophthora inoculum

19. Phytophthora infected rhododendrons Discard dying plants quickly to reduce spreading disease to adjacent plants

20. Potential rooting medium contamination from cull piles or incorporation of non-composted material

21. Home-made steam sterilizer Clean or sterilization rooting medium and containers is essential in reducing Rhizoctonia

22. Bacterial slime/ooze Xanthomonas bacterial wilt of banana Ralstonia

23. Acidovorax anthurii on Anthurium Scout for disease twice a week

24. Scout plants, provide good air flow

25. Drip irrigation to keep foliage dry

26. Wash hands immediately after touching infected plants

27. Sanitation! Follow good sanitation practices Use clean pots, rooting medium, benches, tools, etc. Disinfest tools, benches, everything Bleach quaternary ammonium hydrogen dioxide Begin a habit of washing hands after handling infected plants Remove infected plants immediately Inspect newly arriving plants – don’t bring in diseases

28. 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)

29. Use Fungicides to Increase Lag Phase of Epidemic