Clean Production Practices
- 6.1. Workers and Visitors
- 6.2. Nursery Design, Layout, and Workflow
- 6.3. Benches and Growing Areas
- 6.4. Tools, Surfaces, and the Nursery Environment
- 6.5. Other Cultural Inputs
- 6.6. Inspection and Testing
6.1 Workers and Visitors
Objective
Ensure that all personnel that work in or visit the nursery consistently follow phytosanitary practices.
Guiding Principles
Everyone who works in the nursery needs to understand how Phytophthora spreads and how to avoid spreading it. For many, this will require substantial changes in thinking about how they go about tasks in the nursery. Personal protective equipment may need to be worn for some sanitizing procedures. Personal protective equipment that is reused needs to be cleaned and/or sanitized as appropriate. Visitors will be less informed about phytosanitary practices, so you need to ensure that they follow proper protocols or exclude them from clean areas of the nursery. This practice is applied in any critically clean situation in many industries.
Best Practices
| 6.1.1 | Nursery workers should be trained in approved phytosanitary procedures and follow the procedures at all times. Make sure nursery workers have access to resources that discuss BMPs and clean nursery practices so they understand how Phytophthora spreads and the reasons for clean working practices. Encourage workers to ask questions if they are unclear about procedures or their rationale. |
| 6.1.2 | Clothing worn in clean areas of the nursery should be free of contamination. Don’t enter clean areas wearing clothes that may have soil from your yard, other landscaped areas, field sites, trails, or other potentially contaminated areas. Change clothes or use a removable outer layer (apron, smock, or coveralls) if you will be working with contaminated materials (e.g., cleaning used pots) before working in clean nursery areas. Ensure personal protective equipment is clean and sanitized as appropriate. |
| 6.1.3 | Footwear should be cleaned and sanitized before entering clean areas of the nursery. Clean off all soil and detritus first and finish by soaking the soles and contaminated portions of the uppers with a disinfectant (e.g., 70% alcohol). |
| 6.1.4 | Use waterproof gloves when possible and clean and sanitize regularly (or discard as needed if using disposables). Use separate gloves for highly contaminated operations such as cleaning used pots. |
| 6.1.5 | Leather or fabric gloves are hard to sanitize and keep free of soil particles and should be avoided. Where use of these gloves is necessary, use multiple washable pairs and change into clean gloves if gloves become contaminated or when switching between activities that could result in cross contamination. |
| 6.1.6 | Don’t allow volunteers or other workers to bring home gardening gloves into the nursery unless they are freshly laundered. |
| 6.1.7 | If not using gloves, wash hands thoroughly with soap and water or hand sanitizer (quaternary ammonium or alcohol based) making sure clean off all adhering soil. |
| 6.1.8 | Require nursery visitors to follow the phytosanitary procedures that would apply to nursery workers, including clean clothes, shoes, and hands. Don’t allow visitors to enter clean areas or handle plants or clean materials without following the appropriate phytosanitary procedures. |
| 6.1.9 | Because information related to Phytophthora and other pests and diseases continues to expand and recommendations may change, keep in touch with the latest research and regulatory findings. |
6.2 Nursery Design, Layout, and Workflow
Objective
Use the design and layout of the nursery to reduce opportunities for introducing contamination into plant stock.
Guiding Principles
The propagation and production areas of the nursery need to be maintained as clean areas. Nurseries also have areas that are not clean, such as quarantine areas for potentially contaminated plants and contaminated areas where materials from outside of the nursery arrive. Organizing the nursery layout to separate clean and contaminated areas and activities will help reduce opportunities for spreading contamination into clean areas.
Best Practices
| 6.2.1 | Assess the areas adjacent to the nursery to determine whether they could serve as sources of contamination via flowing water, mud flows, blowing soil or debris, or splash from roads or vegetation. Install drainage, fencing, and barriers where appropriate to mitigate contamination from off-site sources. |
| 6.2.2 | Consider worst-case conditions (heavy rainfall, high winds, etc.) when designing mitigation measures such as drainage to ensure that these measures will be effective across the whole range of likely weather conditions. |
| 6.2.3 | Maximize separation between clean and potentially contaminated areas. Don’t situate contaminated areas (e.g., trash bins, dirty pot piles) where runoff, splash, or wind can move contaminated soil, water, or debris into clean areas. Separation between clean and contaminated areas should be at least 3 m (10 ft). Solid barriers that prevent movement of contamination may be used where this minimum separation distance cannot be achieved or where other circumstances warrant. |
| 6.2.4 | Use barriers and controlled access to restrict movement from contaminated to clean and require sanitation at entry points into clean areas. |
| 6.2.5 | Keep the size of contaminated areas to a minimum. Use solid surfaces, catchments, and drains to capture and remove contaminated soil, debris, and runoff to minimize opportunities for spread into clean areas. |
| 6.2.6 | Use closed bins or dumpsters for disposal rather than cull piles that can serve as sources of contamination. Areas for handling and discarding culls should be outside of the nursery clean areas and should not be located where wind or flowing water could carry contamination into the nursery. |
| 6.2.7 | Organize the flow of work in the nursery so that contamination from old plants, containers, and soil won’t be spread to clean materials and areas. |
| 6.2.8 | Consider how and where deliveries are made and avoid having contaminated vehicles and equipment enter clean production areas. Any vehicles entering clean areas of the nursery should be free of soil and debris. |
| 6.2.9 | Use signage at all access points that specify decontamination procedures required before entry. Use signage to emphasize clean working practices. |
| 6.2.10 | Establish wash and decontamination stations that are easy to use at all entrances to clean areas. |
| 6.2.11 | Make it easy for workers to follow clean production practices. Install hangers to keep hose ends off the ground. Have sanitation supplies such as brushes and disinfectant sprayers staged in convenient spots in working areas or have workers carry these supplies on their toolbelts. Use an easily cleanable cart equipped with sanitation supplies that can be used as a clean working surface in the nursery. |
| 6.2.12 | Potting benches and similar areas that need to be decontaminated frequently should be made of nonporous materials that are easy to clean and sanitize. |
6.3 Benches and Growing Areas
Objectives
Provide enough space between plants and potential sources of contamination to minimize the risk of contamination via water splash.
Guiding Principles
The ground surface, even if it is covered with gravel or landscape fabric, is nearly impossible to maintain as a clean surface. The common practice of placing containers on or near the ground is generally not compatible with clean production.
Best Practices
| 6.3.1 | Keep all plants on benches that provide at least 0.76 m (2.5 ft) of distance between the bottom of plant pots and the underlying surface to minimize the risk of contamination via water splash. Increasing the minimum height to 0.9 m (3 ft) provides a greater margin of safety (see rule of thumb 6). |
| 6.3.2 | Bench tops should be made of expanded wire mesh or other open, nonporous materials that do not allow water to move between pots and can be effectively sanitized. Plywood, wood pallets, or similar solid surfaces that allow water to pool or run laterally are not acceptable. Do not use benches that have wide horizontal surfaces that can catch and hold water or debris. |
| 6.3.3 | Wood is difficult to keep clean and to sanitize, so its use in nursery benches is generally discouraged. Wood is acceptable in applications such as upright members (bench legs) or other supports that do not catch soil, water, plant debris, etc. |
| 6.3.4 | Manage surfaces underneath benches, in walkways, driveways, and elsewhere in the clean area to prevent puddles, eliminate potential for splash, and remain free of weedy vegetation. Maintain adequate drainage and use gravel, landscape fabric, pavers, concrete, or other materials to keep underlying soil covered and avoid having exposed wet soil or mud. |
| 6.3.5 | Allow as much horizontal space as possible between benches and between blocks of plants within benches to minimize the potential for cross contamination via splash. Where it is not practical to provide a relatively safe gap of about 1 to 1.5 m (3.2 to 5 ft), barriers made of plastic film, acrylic sheets, etc., can be used to prevent cross-contamination via water splash between adjacent blocks on a bench. Note that if contamination is detected, all plants within splash distance of a Phytophthora-infected plant or block of plants need to be quarantined for further testing or discarded, so maintaining separation helps localize spot infestations to the fewest plants possible. |
| 6.3.6 | Increase spacing between containers within blocks where possible to reduce the potential for splash contamination between containers. |
6.4 Tools, Surfaces, and the Nursery Environment
Objectives
Use thought and care in all aspects of plant handling to prevent contamination in various plant production and maintenance activities.
Guiding Principles
If in doubt, sanitize surfaces, tools, and hands directly before they are used with clean materials. Some redundancy in maintaining sanitation will not cause harm, whereas skipping sanitation because something is supposed to be clean can lead to accidental contamination. Do not allow water, soil, or debris from contaminated items and surfaces (including the ground) to be transferred to clean plants or surfaces. Avoid moving soil or splashing water between plants.
Best Practices
| 6.4.1 | Provide disinfectant footbaths or other decontamination supplies (brushes and disinfectant sprayers) for sanitizing footwear at all entrances to clean areas. Footwear, including grooves in soles, should be free of visible soil and debris before entering clean areas. Workers may alternatively use dedicated clean, sanitized shoes or boots that are stored and and used only in the clean area. Sanitize these at least daily. |
| 6.4.2 | Items (including workers’ gloves or hands) that have been in contact with the ground or other potentially contaminated surfaces or materials must be sanitized before being placed in contact with clean plant materials, pots, soil, or benches. |
| 6.4.3 | Do not insert unsanitized items in the plant potting media (including your finger to check moisture). If you need to probe in to the pots of multiple plants, use clean and sanitized tools, implements, fingers, etc., as you move from plant to plant. |
| 6.4.4 | Clean and sanitize hands, surfaces, and implements periodically when handling many plants successively in operations such as repotting. Clean and sanitize hands, gloves, tools, etc., when switching between different blocks of plants. |
| 6.4.5 | Assign tools and equipment for exclusive use in the clean production area. Heat-treated potting media should also have dedicated clean tools. Provide clean storage areas where tools can be stored off the ground and away from splashing water. Tools and equipment should be stored clean and sanitized before use. |
| 6.4.6 | Avoid unnecessary handling, rearranging, and moving of plants. Handling increases chances for contamination. Rearranging plants can obscure patterns that might indicate a disease or pest problem and can also increase the chances for spread by giving infected plants new sets of neighbors. |
| 6.4.7 | Do not place container stock on the ground or unsanitized surfaces at any point. Plants that are potentially contaminated though improper handling should be discarded or moved to a quarantine area and not left in clean areas. It is better to lose one plant than to risk contaminating an entire block. |
| 6.4.8 | Place plants and other clean items only on clean or sanitized surfaces if it is necessary to move them. Clean intact sheets of plastic or paper may be used as a clean working surface. |
| 6.4.9 | Clean and sanitize benches before placing a different set of plants or other clean items on them. |
| 6.4.10 | Remove suspected diseased plants as soon as problems are seen. Transfer to a quarantine area for testing. Note the locations on the bench by leaving empty spots and make notes indicating date, symptoms, and test results. Monitor and test adjacent plants as appropriate (see 6.6. Inspection and testing below). |
| 6.4.11 | Promptly dispose of culls and disposable contaminated materials by placing them in a closed waste container. Do not maintain containers of contaminated waste or culls in the clean area. After use, take them to the waste disposal area and clean and sanitize the container before bringing it back to the clean area. Alternatively, use disposable bags for waste collection, seal, and take directly to the waste disposal area. |
| 6.4.12 | Maintain general cleanliness in the nursery by removing plant debris and spilled potting media. Avoid creating dust and splash when cleaning. |
6.5 Other Cultural Inputs
A. Irrigation Practices
Objective
Manage all cultural inputs to minimize the risk of contamination and facilitate rapid detection of root disease if it develops.
Guiding Principles
Phytophthora-caused diseases, as well as those caused by many other plant pathogens, are favored by the moist and crowded conditions found in many plant nurseries. Chemicals that suppress Phytophthora symptom expression in the nursery do not eliminate Phytophthora infections.
Best Practices
| 6.5.1 | Use low water pressure and small droplet sizes when irrigating to minimize splash between containers. Use drip irrigation where feasible to minimize the potential for splash between containers. Thoroughly sanitize drip irrigation equipment whenever it is moved between different plants. |
| 6.5.2 | Schedule overhead irrigations to minimize the duration of leaf wetness. |
| 6.5.3 | Avoid excessive irrigation or stressing plants with inadequate water. Consider water loss from evapotranspiration, inputs from rainfall, size of plants and containers, and other factors when scheduling irrigations. |
| 6.5.4 | Keep irrigation wands, nozzles, and hose ends at least 3 feet (1 m) off the ground on clean, sanitized hooks or racks. The same standard applies to any portion of a hose that may come in contact with or will be held over plants or benches during use. Resanitize these items after any contact with the ground or other potentially contaminated surfaces. Overhead hose reels (like those used in auto shops) are somewhat expensive, but potentially an easy way to avoid contaminated hoses in a small nursery. |
B. Applied Amendments and Chemicals
Objective
Do not apply materials to plants that may be contaminated with pathogens or that will interfere with the testing procedures used to detect and eliminate infected plants in the nursery.
Guiding Principles
Chemicals and biological control agents used to manage Phytophthora in nursery plants suppress symptom expression but do not eliminate Phytophthora infections. Early detection of a Phytophthora introduction into the nursery may be thwarted by use of these chemicals, allowing spread to occur undetected. Infected plants may show no obvious symptoms, but when planted into the field, disease suppression declines as the chemicals degrade. The pathogens can resume activity, leading to both plant decline and infestation of the planting site. See How Using Fungicides in Nurseries Can Increase the Risk of Moving Phytophthora to Planting Sites for a more complete discussion on this topic.
Best Practices
| 6.5.5 | Do not apply materials to plants (e.g., compost tea, organic amendments, organic fertilizers) unless you have reliable documentation that they
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| 6.5.6 | Do not use systemic oomycete suppressive compounds (commonly called “fungicides”, labeled for use against Phytophthora). These compounds suppress Phytophthora and can interfere with Phytophthora detection, but do not eliminate infections. These include fertilizers containing phosphite or phosphonate salts (note: phosphites have suppressive activity against Phytophthora diseases; phosphates are fertilizers with no such activity). |
| 6.5.7 | Biological control agents (e.g., soil bacteria or fungi) or other microbial additives applied to plants or potting media must be free of plant pathogens. The use of such agents is discouraged due to their potential to interfere with Phytophthora detection. |
6.6 Inspection and Testing
Objective
Identify potentially diseased material at the earliest possible stage so it can be culled in a timely manner to prevent further spread in the nursery. Note that with clean inputs and clean production practices, the need for testing will be minimized and tests should show no Phytophthora detections. If Phytophthora contamination is detected in the nursery, you will need to reevaluate your practices (see 7. Record Keeping below) and look for possible avenues of contamination.
Guiding Principles
Most of the Phytophthora species currently circulating in nurseries cause decay of fine feeder roots, though some may progress to cause lethal basal cankers. Decay of fine roots alone can result in stunting and drought stress symptoms, because affected plants have reduced capacity to absorb water and nutrients. In nursery situations, plants commonly get plenty of water and nutrients and have low evaporative demand due to shading and high humidity. Under these nursery conditions, plants that are drought tolerant, like many California natives, can survive and show no obvious top symptoms even if they have very few functioning roots. Although visual inspection of the tops is of limited use for detecting root rots, close attention to plant appearance (e.g., off-color) and patterns of growth (e.g., stunting, low vigor) in a batch of plants can help you spot plants or sets of plants that should be tested. Various Phytophthora species, including many that mainly cause root rot, can also cause foliar blighting or stem cankers if they are splashed onto shoots and leaves. These shoot and leaf symptoms can be detected by careful inspection, though testing is needed to confirm whether such symptoms are due to Phytophthora.
Routine testing for Phytophthora in production areas should be conducted as a quality control measure. Individual plant tests are warranted when symptoms suggest that plants may be infected. Bench-level tests are needed to follow up on detections and are useful for quality assurance. Not all test protocols are equally useful for all situations. Most tests will identify highly-infected plants, but to detect low levels of disease in asymptomatic plants, the proverbial “needle in a haystack”, tests that depend on small samples from one or a few plants will be very inefficient and result in false negatives. See Phytophthora Testing Procedures for BMPs for Producing Clean Nursery Stock for more information.
Best Practices
| 6.6.1 | Visually inspect all plants regularly and frequently (at least weekly) for poor plant growth or appearance. You can use photos from a fixed point to help compare appearance over time. Symptoms in Phytophthora-infected plants may include (in order of increasing severity): low vigor, stunting, off color, intermittent wilting or water stress symptoms, leaf dieback or blighting, root collar and/or stem cankers, whole plant wilting or necrosis. |
| 6.6.2 | Look for patterns of symptoms in the block that may suggest spread from one or more infected plants. This will not be possible if you rearrange plants on the bench. |
| 6.6.3 | Remove suspected diseased plants from the clean production area in a manner that will prevent contamination of other remaining plants. In particular, don't let water or potting media from removed containers fall into other containers or onto clean surfaces. Place pots directly in a plastic bag or clean container before moving. |
| 6.6.4 | The positions of culled plants on a bench should remain unoccupied at least until testing has been completed. Quarantine adjacent plants (hold in place without selling or moving) within 2 m (6.5 ft) ft of suspected diseased plants until testing is completed. |
| 6.6.5 | Remove suspected diseased plants from the clean area to a contained, cleanable surface to inspect the root system. Look at as much of the root system as possible by separating roots from the potting media; rinse with water if needed to see roots more clearly. Roots with severe Phytophthora root rot may have roots that appear discolored, mushy or decorticated (outer soft tissues slough off, leaving only the woody vascular tissues). In less decayed roots, you many only see decay or discoloration of small side roots or newly-emerging root tips and overall root growth may be less than expected. There may be areas of apparently healthy roots and others that show decay. At early stages of disease or in some species it may be difficult to see any clear symptoms of disease. |
| 6.6.6 | Plants with possible disease symptoms and surrounding plants should be tested for the presence of Phytophthora, or other pathogens if appropriate (see Phytophthora Testing Procedures for BMPs for Producing Clean Nursery Stock. |
| 6.6.7 | If Phytophthora is detected within a block of plants, the entire block should be considered to be contaminated. Further testing should be conducted to determine whether the contamination is associated with one or more batches or is associated with the block (see definitions). Use bench level testing or other methods to test the suspect block and other plants from the same batch that are in other blocks. |
| 6.6.8 | Dispose of all plants in contiguous blocks that test positive for Phytophthora. Quarantine and continue to test blocks within splash distance (typically 1.5 m [5 ft]) of any known positive block until you determine the limits of the infected plant material. Plants adjacent to a detection can be considered uninfected if no detections are made in two successive tests conducted at least 2 weeks apart under suitable test conditions. If the detected pathogen is under quarantine or regulation (e.g., P. ramorum) additional rules and protocols may apply. |
| 6.6.9 | Thoroughly sanitize bench surfaces, irrigation equipment, and other items and surfaces that may have been in contact with Phytophthora-infected plants. |
| 6.6.10 | Seek diagnostic help from qualified experts if you encounter unfamiliar pests or disease symptoms. |
| 6.6.11 | Bench level testing can be used to test for the presence of Phytophthora in blocks of plants that do not show obvious symptoms as a quality control check. Emphasize testing of higher risk material (e.g., older plants, plants from tier 2 or 3 propagules), and test material before upsizing to larger containers. See Sample size and sample selection for additional details on selecting plants for testing. |