Best Management Practices for Producing Clean Nursery Stock

2. Clean planting materials

Objective: start with propagative material that is free from infection or external contamination by Phytophthora species as well as other possible pathogens.

What you need to know:  Phytophthora propagules can move in infested soil and water.  Water splash can disperse spores at least up to a height of about 0.6 m (2 ft) and a horizontal distance of 1.5 m (5 ft) (see Basic Rule of Thumb 6 above).  Spores splashed from the soil surface can initiate above-ground infections of flowers, leaves, and stems.  Seeds lying on infested soil can become infested or infected, especially under moist conditions.  Infested or infected propagules can introduce Phytophthora into the nursery, where it can develop and spread.  Tools and boots contaminated with soil containing Phytophthora spores can introduce Phytophthora species from outside areas into the nursery, or conversely into seed or collecting areas outside the nursery.

Best practices:

2.1.  Don’t collect plant materials for propagation in areas known or likely to be infested with Phytophthora.  Only a small percentage of the Phytophthora-infested areas that exist have been documented.  As a general rule, assume that nurseries and cultivated landscapes (yards, gardens, parks, botanical gardens, arboreta, etc.) have the potential to be infested.  Some natural areas, including portions of regional or state parks, open spaces, ecological reserves, and private lands are also infested.

2.2.  Collect seeds, cuttings, or other propagules only from plants and fruit that appear healthy. Do not collect or store seeds or other propagules with apparent disease symptoms such as decay, atypical discoloration, or fungal fruiting bodies. 

2.3. Don't collect seed from the ground.  Collect seeds and cuttings as high above the ground as possible, preferably at least 1 m (3 ft) above the soil surface.

2.4.  Don't collect during wet or muddy conditions.

2.5. Collect propagules with clean hands/gloves and equipment (pruning shears, etc.) and place them in new bags/envelopes and new or clean containers.  Sanitize gloves, hands, and tools immediately if they come in contact with soil.  Sanitize cutting tools frequently.

2.4. Do your part to avoid introducing Phytophthora into seed collection areas.  Make sure your equipment, vehicle, and footwear are clean.  Clean and sanitize your footwear and tools between locations.

2.5. Conduct all processing of seeds or cuttings in a clean work area with clean equipment and clean hands or gloves.  Discard or sanitize any seed or propagule that is dropped on the ground or comes in contact with contaminated surfaces or materials.

2.6. Clean seed as soon as possible after collection to remove any debris before storage and stratification.  Inspect stored seeds or other propagules regularly and discard materials that develop symptoms in storage. 

2.7. Do not bring potentially infected or contaminated plant material into clean production areas of the nursery.  Properly collected seed and tip cuttings (described above) will normally be free of Phytophthora.

2.8. Plant propagules that have been in contact with the soil (divisions, tubers, rhizomes, bulbs, etc.) have an elevated risk of being infected or contaminated with Phytophthora or other soilborne pathogens.  Plant stock originating from such propagules should be segregated from planting material started from cleaner sources, such as seed or cuttings.  See Propagating from field-grown plants for a more complete discussion about the implications of using propagules from soil.

2.9. Plant propagules from the soil (divisions, tubers, rhizomes, bulbs, etc.) should be thoroughly cleaned to remove soil and inspected.  Discard propagules that show evidence of decay.  Surface contamination can be removed with treatments such as diluted bleach dips, but surface treatments will not eliminate internal infections.  Internal infections can only be eliminated by heat treatments, but not all plant propagules will tolerate temperatures needed to kill Phytophthora infections (see Phytosanitary Procedures for BMPs for Producing Clean Nursery Stock).

2.10. Assume nursery stock from others is infested and do not bring such material into clean production areas of the nursery.  If a native plant nursery or other grower has had a well-documented and certifiable clean production system in place for the entire time that their current inventory has been in existence, the stock may be clean.  Place such material in quarantine for at least 3-4 months for observation and testing.