GREENHOUSE
SANITATION
Jean Williams-Woodward
Extension Plant Pathologist
UGA
Disease Triangle
Stressed or
injured
plant
Host
Pathogen
Disease
Capable of
causing
disease (many
are host
specific)
Environment
WATER!
(wet foliage or soils, high humidity, poor air circulation)
Plant diseases are caused by…
• Fungi
• Bacteria
• Viruses
• Nematodes
• Phytoplasmas
• Aster Yellows
80%
10%
5%
5%
Pathogens are spread by…
• Foliar pathogens:
• Soilborne pathogens:
• Water
• Soil
• Wind
• Water
• Insects
• Insects
• Grafting
• Plants
• Pruning/pinching
• Seed
• Vegetative propagation
• Worker activity
• 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
Ralstonia
Xanthomonas bacterial wilt of banana
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
120
100
No fungicide
Spray #1
Spray #2
Spray #3
Spray #4
80
60
40
20
22
9/
15
8
9/
9/
1
9/
25
8/
18
8/
11
8/
4
8/
28
7/
21
7/
7/
14
0