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