Greenhouse Sanitation
Diseases are a major concern for greenhouse growers and can
be a key limitation to profitable plant production. Disease management in greenhouses is critical
because the warm, humid environment in these structures provides optimal
conditions for reproduction of many fungal and bacterial pathogens. When disease management is neglected,
pathogen populations build-up and continue to increase as long as there is
susceptible plant tissue available for infection and disease development. Infected plant tissue, infested soil, and
pathogen inoculum all serve as sources of pathogens that can later infect
healthy plants. Removal of any material
that can harbor pathogens is the basis for disease management using sanitation
practices. This prevents spread of pathogens
to healthy plants or reduces survival from one cropping cycle to another.
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(Kara Keeton, Kentucky Farm Bureau)
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Importance of
Sanitation. Reduction of fungal and
bacterial pathogens by various sanitation practices can reduce both active and dormant
inoculum (infective pathogenic tissue).
While actively growing plants can provide host tissue for pathogen
multiplication and sporulation, dead plant material can harbor overwintering
propagules (fungal spores and bacterial cells) for months or years. These propagules can travel through wind/fan
currents, stick to shoes or tools, or move with contaminated soil or water
droplets.
Sanitation is one of the most overlooked disease management
practices. Often, growers presume that
fungicides are the most important disease management tool at their
disposal. However basic cultural
practices such as sanitation help reduce pathogen numbers and eliminate infective
propagules that cause disease. Poor
sanitation practices allow pathogens to spread to healthy plants or to survive
from one cropping cycle to another. Elimination
and reduction of pathogens can help prevent “overwhelming” of spray programs in
which surviving propagules cause disease epidemics within greenhouses.
Sanitation should be considered by both conventional and
organic growers.
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Water mold pathogens are often spread by contaminated soil
or water. They can also overwinter in
plant debris under benches or on containers and trays that are not properly
sanitized (C. Kaiser).
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Disease Management. Elimination and/or reduction of pathogens
from greenhouses results in fewer fungal propagules. The following sanitation practices can reduce
amounts of infectious pathogens:
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Discard plants that are heavily infected and
those with untreatable diseases (e.g. root rots). Some diseases (e.g. leaf spots) can be managed
using fungicides; isolate infected plants until disease is eliminated. Fungicides won’t bring dead tissue back to
life, but using fungicides will help protect new growth, allowing plants to
overcome disease outbreaks. Contact your
local Extension agent for more information.
·
If infected plants are to be treated with
fungicides, prune or remove infected tissue (flowers, leaves) to eliminate
sources for spore production or propagule multiplication before fungicide
application.
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Leaf spot fungi often produce hundreds or thousands of
spores that are carried by wind currents or on clothing. Many leaf spot diseases can carry over from
one crop to the next on weeds that are left under benches or on alternate crops
on nearby benches (J. Hartman).
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Discard prunings and culled plants. Never leave cuttings in greenhouses, as
pathogens may continue to multiply by producing spores or other
propagules. Do not compost cuttings or
soil because incomplete composting (temperatures below 160 F may result in
survival of propagules.
·
Remove weeds and volunteer plants to prevent
establishment of a “green bridge” between crops. A green bridge allows pathogens to infect
alternate hosts until a more suitable one becomes available.
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Do not reuse soil or potting media. Do not bring outside soil into greenhouses. Use sterilized potting mix only.
·
Disinfest pots, benches, floors, and tools to
remove spores and propagules. Use a
commercial disinfectant such as Green-Shield®, 10% bleach, or 10% Lysol®
concentrated disinfectant. Note: bleach is corrosive, so tools must be rinsed
after 5 to 10 minutes of exposure.
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Many soilborne pathogens produce overwintering or survival
structures (in this case, the tan spherical structures) that can remain dormant
for months or years (D. Hershman).
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·
Clean excess soil and plant debris from floors
and benches. Soilborne pathogens can
remain dormant in soil for months or years, becoming infective when temperature
and humidity increase or when susceptible plant material becomes available.
·
Do not drag hoses and other tools along floors,
where infested soil and plant debris can stick and be moved to clean surfaces.
·
Use pathogen-free irrigation water – either
municipal water or sterilized. Install a
water-treatment system if using recycled pond water.
·
Ideally, a sanitation regime should begin with
an empty greenhouse. Clean and sanitize
all surfaces to insure that pathogens are not carried over from one season to
the next.
·
Use foot baths containing sanitizers to prevent
carrying propagules to clean areas.
Additional Resources
Controlling Phytophthora Root Rot in
Greenhouse Ornamentals, PPFS-OR-H-9
Managing the Greenhouse Environment to
Control Plant Diseases, PPFS-GH-1
Damping-off of Vegetables and Herbaceous
Ornamentals, PPFS-GEN-3
