Sanitation Guidelines for Management of Pests and Diseases of Greenhouse Vegetables
Table of Contents
Sanitation is an important cultural strategy for reducing the impact of pests and diseases on greenhouse vegetable crops. Generally, sanitation involves the removal of both infested materials and potential sources of infestation, followed by disinfection of surfaces.
Various levels of sanitation should be implemented within the greenhouse. During crop production, basic sanitation takes place to suppress development of pests and diseases. However, at the end of each year, before re-planting of the spring crops, a major sanitation exercise occurs. This entails not only removing all plant material but also subsequently cleaning and disinfecting the greenhouse structure and equipment used within it. This process minimizes carryover of pests and disease sources to the new crop, thereby facilitating a clean start for the new crops. The benefits of a clean start include:
For maximum impact, sanitation measures should be practised at all stages of production, beginning with propagation all the way to the end of the crop.
As much as possible, purchase seed that has been treated to exclude disease organisms. Seeds can harbour several pathogens, such as those causing bacterial and viral diseases. Keep seedlings clean by never placing them directly on dirty floors (Figure 1). This can damage roots and infect them with soil-borne diseases such as Pythium and Fusarium root rot. It is imperative to examine all transplants from the plant propagator so that diseased or pest-infested plants can be discarded or treated immediately (Figure 2).
Figure 1. Pepper transplants on clean floor in propagation house.
Figure 2. Transplants about to be planted in production house.
Monitor seedlings and transplants at least once a week for early signs of pest damage or disease symptoms. Use yellow sticky cards (Figure 3) for early detection of arthropod pests such as whiteflies, fungus gnats, thrips and aphids. Place traps along walkways and close to doorways and air intakes, since that is where the pests are likely to enter the greenhouse. Inspect the traps at least weekly.
Figure 3. Yellow sticky card used for monitoring of pests in cucumber seedlings.
Remove potential sources of pests & diseases
Figure 4. Rack of clean lab coats for visitors.
Figure 5. Visitor dressed in lab coat and plastic shoe covers.
Figure 6. Visitor dressed in coveralls and disinfected boots.
Figure 7. Footbath at edge of propagation area.
Figure 8. Disinfection mat for small vehicles at greenhouse entrance.
For more efficient and effective management of pests and diseases, regularly monitor pests using sticky cards (Figures 9 and 10) and inspect the crop for early detection of pests and disease.
Figure 9. Yellow sticky cards used for monitoring young crop.
Figure 10. Yellow sticky card at top of canopy in older crop.
Minimize spread of infectious diseases (for example, bacterial canker, Tobacco mosaic virus, Pepino mosaic virus, etc.)
Infected plant material
Figure 11. Covered bin for garbage bags containing discarded plant material.
Figure 12. Footbath consisting of a pad moistened with disinfectant.
Figure 13. Automatic footbath consisting of mechanical brushes and sprayed disinfectant.
Figure 14. Disinfectant dispenser placed at the greenhouse entrance.
Figure 15. Mechanical disinfectant dispenser.
Workers & equipment
Figure 16. Worker in regularly laundered uniform.
Crates, carts & packing
Figure 17. Workers' cart kept clean by washing and disinfecting at end of each day.
Figure 18. Walkway being mechanically cleaned.
Figure 19. Wide strip of lawn around greenhouse to suppress growth of weeds.
To minimize carryover of pests and diseases, it is best to have a crop-free period. This means not having any overlap between the new crop and the old one on a single operation. Overlapping occurs when a fall crop is interplanted with transplants for the spring crop or when spring transplants are planted while an old crop is still standing in another part of the same operation. Avoiding overlap is particularly important for breaking the cycle of persistent disease organisms and pests that disrupt a biological control program in the new crop.
To reduce carryover of arthropod pests, crops may be treated before removal and shortly after the last harvest. This timing minimizes the opportunity for them to disperse and hide in the ground under plastic sheeting or in the cracks and crevices in the greenhouse structure. It also prevents the pests from moving outdoors to overwinter in weeds or entering neighbouring greenhouses. During treatment, maintain warm temperatures (25-30°C) to keep the pests active and therefore more susceptible to pesticides. These treatments may be chemical or non-chemical, as described below.
Applying effective pesticides before and after crop removal usually reduces most of the insect and mite pest populations. As with the use of any pesticide, follow proper procedures for application and adequately ventilate the greenhouse before re-entering.
Maintain ambient temperatures of about 40°C and a relative humidity of less than 50% for a minimum of 3-4 days to effectively reduce populations of insect and mite pests. This treatment may be repeated after removing the crop. Such an approach is best done during the summer months when warm outdoor temperatures make it easier to increase greenhouse temperatures.
After treatment and removal of the crop, use yellow sticky cards located close to ground level to monitor for any remaining flying pests, such as thrips, whiteflies and aphids. Check these cards often. If any pests are detected, take further remedial action.
Disposal of crop residues
To minimize the survival and dispersal of pests and diseased tissue, remove and properly dispose of residual crop debris immediately (Figure 20). Surface disking plant residues into the soil in adjacent fields is not sufficient. For instance, bacteria that cause bacterial canker can survive for at least 24 months if residues are laying on the surface. However, if the same debris is deeply buried into the soil, survival is reduced to about 7 months. If you cannot remove debris from the site or bury it immediately, place it in covered bins and dispose of it at the landfill site.
Figure 20. Residue of old crop to be removed.
Before disinfection, clean and wash the greenhouse structure and all associated equipment, such as drip stakes, tools, crates, irrigation equipment and vehicles. Debris or organic matter remaining on surfaces can react with the disinfectant and neutralize its active ingredient.
Textured surfaces (for example, cement and wood) may hold organic matter and fungal/bacterial spores that can cause disease in greenhouse plants. Scrub or clean these areas with a detergent or commercial-grade cleaner and a power washer. Note that many disease-causing organisms get lodged on horizontal surfaces, such as on rafters, window ledges and the tops of overhead piping.
For best results, mix disinfectants in warm water (approximately 20°C) and apply the solution to dry surfaces during the evening in a warm greenhouse. Generally, contact time between the disinfectant and a surface should be a minimum of 15-30 min for optimum results. In general, lower temperatures require longer contact times, whereas higher temperatures increase the efficiency of disinfectants.
Figure 21. Greenhouse structure being washed after removal of old crop.
Figure 22. Wet drip stake during washing and disinfection process.
Tools and equipment
Figure 23. Washed and disinfected rollers ready for loading string for the new crop.
Figure 24. Greenhouse equipment that has been washed, disinfected and packed.
Growth media disinfection
New growing media should be used for every crop. However, if the media is to be re-used, then it should be disinfected. Sterilizing growth media will reduce pest carryover, particularly of spider mite and thrips. Between August and September, diapausing mites move downwards from the crop and can hide in rockwool slabs, under the ground-sheet plastics, in crop debris, etc., where they are sheltered until favourable conditions resume. Thrips pupate on the ground and can survive in similar refuges. Older growing media often harbour many disease pathogens that attack the roots. Growth media may be disinfected using steam or fumigation.
To efficiently steam growing media such as soil or any mix of organic components, the media should have a good tilth and be neither too wet nor too dry. Use a soil thermometer to ensure that the media is heated to over 80°C for 30 min. If this temperature or time is exceeded, problems of waterlogging, high salts and ammonia burn may be encountered.
The time required for steaming depends on the wetness of the rockwool and temperature used. Steaming at 90°C for 30 min should be adequate. Generally, the wetter it is, the longer the steaming period. For this reason, the substrate should be as dry as possible before steaming. Rockwool that is stacked on pallets and not wrapped in polyethylene bags can be steam-sterilized in 2 hr. Rockwool wrapped in polyethylene requires 5 hr of steaming. Do not stack the rockwool higher than 1.5 m (5 ft.). To stabilize the stacked slabs, place each row at right angles to the row beneath. In addition, leave a 2.5 cm (1 in.) space between individual slabs to allow for better steam penetration.
Remove all weeds in and around the greenhouse, clearing as large a perimeter as possible. Weeds not only harbour insect and mite pests, they are also a good source of many viruses and other diseases.
Once the greenhouse structure is clean (Figure 25), biosecurity/sanitation practices should be maintained. Use disinfection mats and footbaths at all entrances to ensure that all shoes, vehicle wheels, etc. are clean and disinfected before entering boiler rooms and the greenhouse area. Have coveralls and hand sanitizers available for all visitors. As far as possible, restrict activities of visitors to the main walkways to minimize contact with the crop.
Figure 25. A clean greenhouse ready for planting of new crop.
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