GREENHOUSE SANITATION Jean 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) HostPathogen Environment Disease

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