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Reminders for Cleanup

To minimize carryover of disease-causing organisms to the new crop, and to facilitate management of pests and diseases in the subsequent crop, a good cleanup is essential. Although the procedure for cleanup has become routine in most operations, there are some key points that growers need to remember as they go through the cleanup process.

1. Clean surfaces before Disinfecting - Removing all inorganic (e.g. calcium deposits) and organic residues (e.g. plant debris) is critical to achieving a good cleanup. Inorganic deposits can harbour disease-causing micro-organisms, and organic residues greatly reduce the effectiveness of all disinfectants by interacting with them and providing protection for pathogens. An effective method of cleaning surfaces is use of soap and water applied at high pressure before the disinfection process. Soap is especially useful in removing greasy deposits. A thorough rinsing after washing with soap is best because soap residues can inactivate certain types of disinfectants such as quaternary ammonium compounds.
2. Pay attention to all surfaces - In particular, horizontal surfaces at higher levels in the greenhouse can be overlooked. Many disease-causing organisms are lodged on rafters, window ledges, tops of overhead piping etc. Power-washing from below will not adequately clean such areas. Additionally, extra care is needed in cleaning the textured surfaces of cement, wood, etc. which can hide many kinds of organisms.
3. Note pH effects - Soaps are alkaline and residues can either inactivate certain disinfectants, as mentioned above, or reduce the effectives of those disinfectants that work optimally at an acidic pH. Bearing the influence of pH in mind, it is best to use one type of disinfectant if multiple applications of disinfectants are being made. As long as proper concentrations are used and sufficient contact times are allowed, the disinfectant of choice should be effective. Note also that disinfectants are best applied to dry surfaces because wet surfaces dilute the concentration of the disinfectant applied.
4. Allow sufficient contact time with Disinfectants - Note that no disinfectant works instantaneously. A certain amount of contact time is required for maximum effectiveness, and the time required for contact is influenced by temperature and concentration of the disinfectant. Generally, higher temperatures increase efficiency of disinfectants by two- to three-fold for every 100C rise in temperature whereas lower temperatures do the opposite. For example, the effectiveness of chlorine is reduced by 50% at 100C.
5. Note hardness of water used for Disinfection - Some disinfectants, particularly quaternary ammonium compounds, are deactivated by hard water, i.e. water with high levels of calcium and magnesium. It is advisable to test water for hardness and for contamination before use.
6. Be mindful of Re-contamination - Growers need to maintain sanitation protocols to minimize re-contamination of the "cleansed" greenhouse. So, provision of disinfection boot trays or clean foot wear dedicated to use in the greenhouse, proper cleaning and disinfection of all equipment used in the greenhouse, etc. are in order.

These reminders provide the basis of a good cleanup job. Throughout this process, growers are also reminded to carefully read labels of all products used and to follow safety precautions recommended.