Benjamin Franklin once famously observed: "An ounce of prevention is worth a pound of cure". In actuality, Franklin was talking about fire prevention in the city of Philadelphia. However, he just as easily could have been talking about pest control in greenhouse and high tunnel crops. Prevention always is the easiest cure for pests; in certain cases it's the only cure.
Greenhouse and high tunnel growers who find themselves continually battling certain diseases and insect pests might not be doing an adequate job of greenhouse sanitation. Prevention is one of the basic IPM principles for both disease and insect management, and proper sanitation is the first step in prevention. It is advisable to sanitize a greenhouse as early as possible following the growing season opposed to waiting just before planting the following spring.
Cleaning is the first step in sanitizing and involves physically removing weeds and all living plant material from the greenhouse. The importance of this step cannot be overemphasized since living plant material is an ideal refuge for pests such as aphids, thrips and mites. Plant debris, spilled potting media, etc. also should be eliminated prior to disinfecting a greenhouse. Shop vacuums are useful in removing debris from concrete and covered floors. Additionally, there are cleaning agents on the market (e.g. STRIP-IT™) that can make the job of algae, grime and fertilizer residue removal easier. Using a power washer with soap and water is another possibility. Care must be taken, however, since soap can leave residues that can inactivate certain disinfectants (i.e. the quaternary salts) used later in the sanitation process.
Owners of greenhouses with bare soil or gravel as a floor might consider the installation of weed barriers. In addition to preventing weed growth, weed barriers make algae management easier. Weed barrier should not be used below a gravel greenhouse floor since it tends to trap soil and moisture, creating an ideal environment for weeds, diseases, insects and algae.
After thoroughly cleaning a greenhouse, it should be disinfected. To a certain degree, a number of pathogens (e.g. Pythium or Rhizoctonia) can be managed effectively by the use of disinfectants. Dust particles or other organic residue in the greenhouse might contain bacteria or fungus inoculum which disinfectants can eliminate. In addition to plant pathogens, some disinfectants are also labeled for managing algae. The latter tends to promote populations of fungus gnats and shore flies to develop.
There are four disinfectants commonly used in greenhouses. When possible/practical, rotation between these four is recommended. The four disinfectants include:
For those who produce vegetables in greenhouses or high tunnels using soil culture, sanitation is equally important. As mentioned above, remove all of the debris from the previous crop as possible. Be mindful of weeds around the perimeter of the greenhouse or high tunnel, since weeds harbor insect pests that can serve as vectors for certain plant diseases. Deep cultivation should follow debris and weed removal to bury any plant residue missed deep in the soil.
Good sanitation practices provide growers with a longer pest free window, reducing the need for pesticide and reducing labor and expenses associated with pesticide application. The following graph illustrates how proper sanitation can reduce the need to apply pesticides:
In summary, effective greenhouse and high tunnel management requires growers and managers to develop a "think clean" mindset. Proper sanitation does requires time and attention to detail. However, the benefits of following good sanitation practices will be evident when used effectively and consistently. A clean production facility leads to healthy plants, and healthy plants lead to happy growers and greater profits
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REVISED: February 21, 2017