"Aquatic weeds, the silent invaders of our waterways, pose a particular biosecurity problem for New Zealand" (Biodiversity Strategy 2000).

The success of invasive water weeds in New Zealand is spectacular, at the cost of native biodiversity, hydro-electric power generation and recreational use of our waterways.

NIWA assesses the risks posed by potential aquatic weeds, both within New Zealand and at our borders, and advises on priority species for biosecurity management. The ways (pathways) and means (vectors) how weeds are spread are identified, as are ways to intercept them. The impacts of weeds and their management on the environment are quantified so that the ecological costs and benefits of biosecurity actions are clarified. A major goal is to expand the toolbox of solutions for the control and eradication of aquatic weeds and to best match solutions with specific weed situations.

Articles

Assess threats

Inventory introduced species

• Aquatic plant pests

Assess competitiveness

• Gypsywort warning
• Weeds in waiting

Develop Risk Assessment Models

• Managing tomorrow’s weeds today – a risk assessment approach to aquatic weed management
• Weed risk assessment model
• Hornwort – our worst submerged weed

ID pathways & vectors

• Decontamination of fishing nets and other equipment to prevent transfer of freshwater pet organisms

Advise surveillance strategies

• Spreading the word, not the weed
• Hornwort: a serious threat to South Island lakes

Invasion outcomes

Measure impacts of invasive species

• Hornwort weed impacts on lake bed sediments

Measure impacts of control l

• Diquat Summary – use and safety
• Review of Diquat Reports of Relevance to Iwi Values in Lake Karapiro
• Effects of grass carp on the biota of a Waikato drain

ID risk of hybridisation

• Alien Hybrids

Managing weeds

Trial herbicides for NZ use

• Controlling hydrilla
• Control of hydrilla
• Manchurian wild rice: the alien invader can be stopped
• Managing marginal mayhem
• Hornwort Threatens Lowland Waterways
• Endothall trial for the control of Ceratophyllum demersum in the Wairarapa

Advise integrated management

• Decision Support System
• Weed-busting case studies from the NIWA files