Overview
The end of season cleanup is necessary to help ensure the success of next year's crop. A thorough cleanup is an important component of the pest and disease management program. It can prevent or minimize the carryover of pest and disease problems into the next season.
Crop residue removal
Remove all crop residue from the greenhouse and disposed of it. Depending on your area, there may be facilities that accept crop residue for composting. The spent coir from the grow-bags could also be a welcome addition to compost sites as much decomposition has already occurred during the growing season. Once the crop is removed, increasing the greenhouse temperature to over 25°C for several days can increase the metabolic activity of any pests still in the greenhouse. This can help cause them to die of starvation in the absence of their food source.
Greenhouse cleaning
Wash the interior of the greenhouse with a detergent solution using a pressure washer, and then rinse. The detergent will remove oily residues from the greenhouse and covering material. Following the rinse, apply a registered disinfectant solution to aid in disinfecting the greenhouse structure of any remaining pests and disease organisms.
To avoid a chemical reaction between the disinfectant and the detergent, consult with your supplier before purchasing your products to ensure compatibility. When pressure washing the greenhouse, ensure all safety precautions are taken to prevent direct exposure to the bleach solution.
Equipment
All greenhouse equipment should also be washed and disinfected. Soak dripper stakes, clips and truss supports (tomato greenhouses) overnight in a 10% bleach solution, and then rinse.
Irrigation lines should be flushed with nitric or phosphoric acid at a pH of 1.6 to 1.7 (1 part acid to 50 parts water). Do not allow the acid solution to contact the pH electrode sensors or the E.C. sensors, as they can be damaged. The acid solution should be allowed to sit in the lines for 24 hours at which time the lines should be thoroughly rinsed with water to ensure all acid solution is removed from the lines. For more information, see Maintenance and cleaning of drip irrigation.
Caution: Provide good ventilation through the greenhouse when flushing the lines with acid to avoid the build-up of fumes. Ensure the flushed water does not have a pH of below 5 as dangerous chlorine gas may form.
Slab sterilization
If rockwool slabs are used as the growing media, they can be reused for the upcoming crop. The reuse of rockwool slabs is both environmentally friendly and economical. Good quality slabs can be used for up to 3 years.
Do not reuse slabs that have lost more than 10% of their original height. This is an indication that the structure or ‘profile’ of the slab has changed to the extent that the yield of subsequent plants grown may be reduced significantly.
Steam sterilization can ensure disease organisms do not carry over into the next season. Slabs should be as dry as possible, as dry slabs heat faster than wet slabs.
If the crop has had tomato mosaic virus (TMV) or pepper mild mottle virus (PMMV) the slabs should be heated to 100°C and held at this temperature for 10 minutes. Otherwise, the slabs should be heated to 75°C for 20 minutes. If the slabs are bagged and paletted, they require 5 hours to reach 100°C.
Acknowledgements
Portree, J. 1996. Greenhouse Vegetable Production Guide for Commercial Growers. Province of British Columbia Ministry of Agriculture, Fisheries and Food.