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.
(Kara Keeton, Kentucky Farm Bureau)
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.
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).
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:
· 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.
· 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.
· 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.
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).
· 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.
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