What Anglers Can Do to Prevent Didymo Spreading

Felt-soled wading boot have been identified as a major didymo risk. Instead of felt-soled boots or waders, Fish & Game New Zealand recommend using rubber-soled alternatives that dry rapidly and are easily cleaned.

If using felt-soled boots, it is preferable to restrict them to one river. Always check and remove any didymo before leaving the river, and to decontaminate the soles as best you can.  The Biosecurity New Zealand website advises either:

• Soak for at least 40 minutes in hot water kept above 45 °C, or
• Soak for 30 minutes in hot water kept above 45 °C containing 5% dishwashing detergent or nappy cleaner.
• Freeze until solid: The time required until the boot is frozen solid will vary but freezing overnight should work in most instances.

Check

Before you leave a river or lake, check items and leave debris at site. If you find any later, treat and put in rubbish. Do not wash down drains.

Clean

The Biosecurity New Zealand website advises that  there are several ways to kill didymo. Choose the most practical treatment for your situation which will not adversely affect your gear.

• Non-absorbent items
  Detergent: Soak or spray all surfaces for at least one minute in 5% dishwashing detergent or nappy cleaner (two large cups or 500 mls with water added to make 10 litres); or
  
  Bleach: Soak or spray all surfaces for at least one minute in 2% household bleach (one small cup or 200 mls with water added to make 10 litres); or
  
  Hot water: Soak for at least one minute in very hot water kept above 60 °C (hotter than most tap water) or for at least 20 minutes in hot water kept above 45 °C (uncomfortable to touch).
  
• Absorbent items
  Absorbent items require longer soaking times to allow thorough saturation.
  Felt soled waders, for example, require:
  Hot water: soak for at least 40 minutes in hot water kept above 45 °C; OR
  Hot water plus detergent: soak for 30 minutes in hot water kept above 45 °C containing 5% dishwashing detergent or nappy cleaner; OR
  Freezing: Freezing until solid
• Freezing
  Freezing any item until solid will also kill didymo.

Dry

Drying will kill didymo, but slightly moist didymo can survive for months. To ensure didymo cells are dead by drying, the item must be completely dry to the touch, inside and out, then left dry for at least another 48 hours before use.

Relying on ambient drying as a stand-alone treatment for decontaminating highly absorbent risk goods such as felt-soled waders and boots is not recommended in situations where use between waterways is frequent (daily, weekly or even monthly).

Drying should only be relied upon as a decontamination treatment if great care is taken to actively and completely dry the felt (such as by using a heat source where temperatures around the felt are assured of reaching 30 °C). Once the felt appears dry, complete dryness must be confirmed by a tactile inspection of the felt pile to the base of the fibres. Once completely dry, items must remain dry for at least 48 hours before use in another waterway.

See Didymo Biosecurity Alert

See press releases about felt-soled boots:
- from Fish & Game on 29 January 2007
- from Fish & Game and DOC on 7 December 2007

See the Biosecurity New Zealand website for cleaning methods to use for fishing equipment, waders, clothing. boats, vehicles and tyres.