Weeds in Waterways

We have a knack for bringing wet blustery conditions on our field days and Weeds in Waterways on the 14 April was no exception. Eighteen hardy souls donned their jackets and joined in for a day of information and demonstrations by expert presenters Rebecca Bradley – Senior NRM Manager from South East Local Land Services, Lori Gould – Grass Roots Environmental and John Franklin – Franklin Consulting.

Rebecca Bradley began by explaining the legal obligations of farmers with regard to weed management in NSW. The Biosecurity Act 2015 came into effect this year and has two key principles: biosecurity is everyone’s responsibility and all land managers have a general biosecurity duty.

All waterways are unique and behave differently depending the geology, soil type, river processes and energy level. You need to have a basic understanding of all aspects of stream behaviour before undertaking ground works. Something that works in one location may not be suitable on your property. Getting good local advice is a must. There are chemical, biological, physical and farm management factors that determine the behaviour of a watercourse. First and second order streams can have structures put in them to mitigate erosion, third order streams require a permit for structures and professional advice should be sought in this situation. See Tapping Into It: Water for Small Farms summary for an explanation about first, second and third order streams.

John Franklin and Lori Gould shared their expertise in managing weeds in waterways including a discussion about willows and managing a riparian restoration project.

Willows friend or foe?

Willows (Salix spp.) are currently identified as a weed of national significance (see weeds of national significance list). They are invasive and well adapted to Australian conditions. Key points about willows:

  1. Willows spread and propagate in different ways depending on the species. They can also form hybrids with each other. Some willows grow from seed, cuttings (that break off the plant and move in the water) and by suckers. Hybrid willows are very vigorous and can reproduce just two or three years after germination.
  2. The replacement of native vegetation by willows adversely affects biodiversity in waterways by reducing habitat and aquatic diversity. Willows create a flush of organic matter when they drop leaves in autumn. This reduces water quality by reducing available oxygen and releasing chemicals that harm small in stream herbivores that are adapted to living with evergreen plants (such as eucalypts).
  3. Willows use much more water than native vegetation in streams and willows in stream beds can divert stream flows, resulting in erosion.
  4. Any willow project should consider what other vegetation there is on the site and whether revegetation is required. Sometimes there is enough remnant vegetation to recolonise once willows are removed. Circumstances where willows shouldn’t be removed (or  removal should be staged) are on eroding outer bends of rivers and creeks and in places where it isn’t cost effective. For example, large infestations where willows are removed without any major environmental benefits, such as sites with willows upstream and downstream and little remnant vegetation. These sites really need a ‘whole of reach’ approach and actions need to be well coordinated. Often these sites become beyond the landholder’s capacity to manage. However, large projects can be a great success such as the Yass River Linkages Project.
  5. If you propose to remove or prune any existing trees or vegetation, you should contact your council first to make sure you don’t need approval for this – look in the Queanbeyan City Council Tree Guide

For more information on willows see the Rivers of Carbon website – What is the problem with Willows?

Some general principles for managing weeds in waterways:

  1. Understand what you have in terms of native vegetation and weeds and do a simple map.
  2. Cooperate with your neighbours where possible.
  3. Prioritise weed control in high asset areas and/or where the weeds are in low numbers, removing weeds by hand or targeted spraying. Start with weeds that are the highest environmental priority (e.g. Serrated Tussock, St Johns Wort and other noxious weeds) and then progress to managing lower priority weeds if appropriate. If weeds are extensive then control may need to be staged from the outside in or from upstream to downstream. The amount that can be achieved will depend on time and budget.
  4. It is generally considered better to poison willows in stream beds and leave them in place, rather than removing them manually using equipment. This reduces the risk of branches snapping off and plants establishing from the cuttings. The best option depends on what assets are downstream (e.g. fences, crossings, bridges).
  5. When planning your project think about what you want to replace the weeds with. Plant a diversity of plants including ground covers, grasses, shrubs and trees. This provides valuable habitat for animals. Use local plant lists and resources from Landcare and Greening Australia to find out what to plant in your area. For example ROC Native Revegetation Species List and Local Native Plant Guide – Molonglo Valley.
  6. Prepare tree planting sites by deep ripping and spraying in autumn and planting in winter and spring. Spraying with herbicide reduces grass competition or scalping is a chemical-free option.
  7. Always water plants in and use tree guards.
  8. Keep monitoring the site for new infestations of weeds and plant health.
  9. Fence off the watercourse and manage grazing to allow the plants to establish. Timed grazing can  be reintroduced once the revegetated trees and shrubs have grown to a suitable size.

Rivers of Carbon in partnership with Greening Australia and other organisations currently has funding for projects in the Burra, Goulburn and Yass areas to assist landholders with revegetation and stream rehabilitation (see Rivers of Carbon Funding Opportunities).

The following fact sheets may be helpful:

You might also like to read our workshop summary Working with Weeds .

This field day was made possible with funding from the Australian Government and in-kind support and funding from South East Local Land Services. Thank you to our sponsors of the network, the Palerang Local Action Network for Sustainability, and our host farm.