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GREENHOUSE SANITATIONJean Williams-Woodward
Extension Plant Pathologist
UGA
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
Plant diseases are caused by…
• Fungi • Bacteria• Viruses• Nematodes• Phytoplasmas
• Aster Yellows
80%
10%
5%
5%
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
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
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
Diseases may be overlooked…
Look more closely…
Closer… Notice the defoliation, leaf spotting
Downy mildew on Knockout Rose
Turn leaf over and look for sporulation
Botrytis blight
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
Root disease
• Plant wilting, off-color, etc.• Pythium, Phytophthora, Rhizoctonia, Thielaviopsis
• Damping off (both pre- and post-emergence)
• Root death, sloughing, discoloration – WET substrate
• Graded, gravel beds or ground-cloth covered gravel can reduce root disease incidence
• Phytophthora and Pythium are water-molds• Require water to spread and infect.• Puddles saturate the rooting medium, as well as channel Phytophthora inoculum
Phytophthora infected rhododendrons
• Discard dying plants quickly to reduce spreading disease to adjacent plants
• Potential rooting medium contamination from cull piles or incorporation of non-composted material
Home-made steam sterilizer
• Clean or sterilization rooting medium and containers is essential in reducing Rhizoctonia
Bacterial slime/ooze
Xanthomonas bacterial wilt of banana
Ralstonia
Acidovorax anthurii on Anthurium
• Scout for disease twice a week
Scout plants, provide good air flow
Drip irrigation to keep foliage dry
Wash hands immediately after touching infected plants
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
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)
Use Fungicides to Increase Lag Phase of Epidemic
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No fungicideSpray #1Spray #2Spray #3Spray #4