Seeds or transplants must be free from pests, diseases, viruses or viroids before bringing into the glasshouse.
Always check, and where possible audit, the seed producer and transplant raisers regarding their biosecurity procedures and ensure the relevant procedures and paperwork are in place. Some resistant or tolerant cultivars are available and worth investigating, especially if there is a particular issue on a nursery and the cultivar is acceptable to customers.
Best practice in handling bought-in plants
AHDB Horticulture Factsheet 06/08 ‘A guide to best practice in handling bought-in plants’ provides advice on goods-in procedures, documentation, nursery hygiene, plant care and the biosecurity measures necessary to help maintain plant quality and ensure plant health requirements are met.
The guidelines from the Factsheet for working with plant suppliers are:
- Seeds and plants should be procured from reputable suppliers who are able to provide high-quality material on a consistent basis
- Seeds and plants must be free from pests, diseases and weeds, and meet specified quality requirements regarding plant size and shape
- Suppliers should also be able to meet quantity requirements and maintain high levels of customer service
- Make sure your suppliers know what you expect and keep you informed of progress or any anticipated problems
- Where it is proposed to use any plant protection products, check with your retailer’s technical documentation to ensure these are permitted in the country of application and for the crops on to which they are applied
- Visit your plant suppliers (propagator) on a regular basis to review progress, ensure your requirements are being met and develop a good working relationship with them. Developing good supply networks is the key to success
- Agree your requirements in writing (consider using pictures to your specification to better illustrate requirements), including your trading terms and conditions
- Check whether your suppliers are part of an industry certification scheme and have traceability systems in place, which include records of cultural work and pesticide applications
Once planted in the nursery, crops should be carefully monitored for pest, disease, virus and viroid issues. Systematic and frequent monitoring is the key to understanding when action needs to be taken. Dedicated staff training to identify issues will give the greatest possible chance of spotting problems at the earliest stage.
If there is an issue identified, the plant, bay and row numbers should be recorded and close attention paid to monitoring that area frequently. Growing and picking methods must minimise any potential spread – e.g. pick problem areas last. Staff can act as vectors for plant-to-plant spread, either physically or through equipment they use to perform the day-to-day growing operations. Daily tasks of crop husbandry, e.g. monitoring, maintenance, leaf removal, pruning, training, twisting heads, applying biocontrols, harvesting, can all be considered as potential spreaders of pests, diseases, viruses or viroids.
Control methods to prevent spread of disease
Particular care must be taken with operations where plants are physically cut using a tool and material from any part of that plant can be transferred to any other plant. This is most likely on harvesting knives, etc. Harvesting tools should be disinfected frequently, at least every row, with suitable disinfectants, such as hydrogen peroxide, peracetic acid or benzoic acid. Skimmed or powdered milk is commonly used to help sanitise knives between plants (milk proteins can reduce the infectivity of some viral particles). Some nurseries use a one-knife-per-row policy, so if an issue occurs spread is restricted to that row alone. Soaking contaminated knives in disinfectant for one hour after use has been shown to reduce spread of disease in crops.
If any plant health issues are suspected, then more stringent control methods in crop work appropriate to the issue are advised; for example, the use of disposable coveralls and gloves (when dealing with bacterial or viral problems), should be changed at the end of every row; the same worker keeps to the same crop rows; all equipment used on suspect plants must be kept separate from other plants and washed regularly in a suitable disinfectant.
Any plants which have developed disease, viral or viroid infection during the cropping season need to be removed immediately from the glasshouse. Where viroid or bacterial infection is present, the slabs should also be removed. This should be done as carefully as possible. Drippers should be removed from slabs and the plants left to wilt for a few hours to prevent spillage of infected liquid feed. Debris should be placed in a plastic bag, which should be sealed before removal. It is important that no infected material is left in the vicinity of the glasshouse, to remove the risk of infection remaining and further affecting the crop, or infecting crops at other nearby nurseries. Any such material must be removed from the growing site and disposed of appropriately at landfill. A good relationship with a plant clinic (such as Fera, STC or EMR) and the local Plant Health and Seed Inspectorate (PHSI) is useful. If unusual or previously unseen symptoms are found, it is worth contacting a plant clinic, and if a notifiable disease is suspected, advice on methodology for removal must be sought from your PHSI inspector.
In general, the glasshouse and surrounding areas should be kept as clean as possible from weeds to reduce the chance of potential infection. At least two metres is considered a minimum, but up to ten is recommended. There should also be attention paid to keeping vehicles clean – wheel disinfectant dips are advised to treat all vehicles entering and leaving the site.
Businesses that have multiple sites must take extra care if transferring staff, equipment (including harvest crates) and crops between locations. There is a high risk of moving pest or disease problems from site to site and this can be a particular issue from overseas. Comprehensive protocols for movement of goods should be in place.