Willows

(Salix species, excluding S. babylonica, S. x calodendron and S. x reichardtii )
    Willows at Perth Bridge

What are willows?

  • Willows are a serious environmental weed.
  • Willows are a declared weed in Tasmania under the Tasmanian Weed Management Act 1999. The importation, sale and distribution of willows are prohibited in Tasmania.
  • Willows are also a Weed of National Significance (WONS).

How to identify willows

  • The appearance of willows varies dramatically between species. For example, willows can be trees or shrubs, smooth or rough barked, long or short leaved, and have flexible or brittle branches. Most willow plants are either male or female.
  • If you are still in doubt about the weed you are dealing with, contact Biosecurity Tasmania on 03 6165 3777 for help.
Post willow removal along Jordan River Willow strike
Image top: Willows near Perth Bridge.
Images above left to right: Post willow removal along the Jordan River, willow strike. 

Willows in Tasmania

  • Willows are a very complex plant group. There are a large number of willow species occurring in Tasmania, including many hybrid species (hybrids are a cross between two closely related species).
  • Of the naturalised taxa, crack willow (S. fragilis var. fragilis) is the most common. It is widely distributed and abundant in the north, east and south. Only male crack willow plants occur in Tasmania.
  • A number of willow taxa not occurring in Tasmania present a large threat due to their weed history on the Australian mainland (eg. S. nigra). There is also a risk that male crack willow will hybridise with other more localized willow species in Tasmania which include female plants, leading to hybrid plants that can then spread by viable seed.
  • Willows are a serious weed of riparian (riverside) habitats in Tasmania. Willows can choke waterways, increase erosion and silting, reduce water availability, and damage aquatic habitats for fauna and flora.

What is the legal status of willows in your area?

  • The legal responsibilities of landholders and other stakeholders in dealing with willows are laid out in the willow Statutory Weed Management Plan.
  • In Tasmania, the widespread crack willow forms a special case and is considered separately in the willow Statutory Weed Management Plan. See Table 1 (Zone A municipalities: crack willow) and Table 3 (Zone B municipalities: crack willow) to find out whether your area falls in an eradication or containment zone for crack willow. See also Table 2 (Zone A municipalities: non-crack willow) to find out whether willow species other than crack willow occur in your municipality.
Detailed management and control guidelines for willows in Tasmania can be found in the DPIPWE Willow Control Guide and Herbicides for Willow Control. Refer also to the Weeds of National Significance - Willows Management Guide for more detailed management information on willows. For further information see DPIPWE's Weed Links and Resources on this site.

 

See also:

Herbicides for Willow Control
Statutory Management Plan for Willows
Useful Weed Resources

Other useful links:

Pest Genie
APVMA

Willow Control Guide

Do

  • Willows can pose a very complex management problem - seek advice. Resources such as best practice management guides can help you plan your control program. Good planning will save time and money in the long-run and provide a more effective result;
  • If there is a chance that you are dealing with seeding willows, act immediately: seeding willows pose the highest threat;
  • Coordinate your control program with neighbouring landholders where your weed problem crosses property boundaries;
  • Take into account the impacts of your control activities on the stream as a whole, and on those living downstream;
  • Consider use a combination of different control methods for large infestations; and
  • Revisit and regularly inspect the site and ensure follow-up is undertaken.

Don't

  • Don't start your control program without first planning your approach;
  • Don't rely on one attempt at removal - follow-up is essential;
  • Don't rely on just one control method;
  • Don't take on too much at one time - many small steps may be better than one big attempt at control; and
  • Don't underestimate how much waste will be produced when you remove willows!

Spread of willow

  • Willows can spread in two ways: sexually, by seed germinating on wet sediment, and asexually, by twigs and branches travelling downstream and rooting on wet ground and in shallow water.
  • Spread by seed only occurs where compatible male and female plants flower at the same time and are close enough to cross pollinate (usually less than 2 km), and where there is wet ground available 1-2 months after seed shed (October to November).
  • Thousands of seeds are released over a short period in spring, so seedlings are typically found as 'galleries' or masses of similarly-sized seedlings growing close together.
  • Asexual spread can occur where branches and twigs break off and spread downstream, and through layering where trunks collapse and branches weep down and root where they touch the soil.
  • As rooted fragments can break off and establish at any time of year, this type of spread typically leads to plants of different ages and sizes.
  • In Tasmania, the widespread crack willow occurs only as male plants, and all spread is via fragmentation.

Integrated management

  • Willow management can be a long-term and expensive process, and eradication is not always either feasible or desirable.
  • Careful planning is therefore essential to avoid waste of resources, and to ensure the desired outcome is achieved.
  • Essential steps in planning willow control include: a clear objective (what you wish to achieve), a clear reason (why is it necessary), who is to be involved, when and where to conduct the works, and how you will review the process.
  • A first step in any control program will typically require mapping of the distribution and extent of an infestation, and the species of willow involved.
  • For large or complex infestations, it may also be necessary to priorotise areas and/or species. For example, seeding willows will usually be a very high priority, while areas of high conservation value or severe impact will attract a higher priority than areas of lower value or lesser impact.
  • Attention must also be given to what to do with the removed material. Remember that fragments of willow left behind may regenerate and un-do all the hard work of removal.
  • Finally, it is imperative to consider the potential impacts of any control actions on the river system itself, and to factor in revegetation where necessary and ongoing monitoring and follow-up control.

Physical removal

  • Willow seedlings and rooted fragments up to 2 years old can be removed by hand.
  • Larger trees will require machinery for physical removal. A range of machinery options are available depending on the site conditions. Always consider occupational health and safety when using machinery to remove willows!
  • On stream banks or other erodible sites root mass should be retained to limit erosion. This will require felling of stems and application of herbicide to the outer rings of the stump. Refer to the Weeds of National Significance - Willows Weed Management Guide.
  • Generally, a combination of physical removal and chemical treatment provides best long-term results.

Waste management methods

  • Don't underestimate how much waste will be produced when you remove willows - willow removal produces and enormous amount of waste material which has to managed.
  • Currently there are only a few waste management methods available, including piling and burning (the most common method of removal), mulching (generally limited to smaller infestations), and feed to stock, furniture and firewood (useful for only small quantities of willow material).

Biological control

  • Biological control is the use of a living species, usually an insect, mite or disease, to control a weed;
  • Biological control will not eradicate willow, but may be used in conjunction with other control methods;
  • No biological control agents for willow that released in Australia at the present time, although this approach has great potential as a willow management tool for the future.
  • For more information on biological control programs in Tasmania contact the Tasmanian Institute of Agriculture.

Chemical control

  • A number of herbicides are registered for use on willow in Tasmania. See Herbicides for Willow Control for more information.
  • Techniques include cut-and-paint and remove material, stem inject and leave material standing, and foliar spray and leave for seedlings up to 2 m.

Herbicides for Willow Control

Herbicides for Willow Control


Important Disclaimer
To the extent permitted by law, the Tasmanian Department of Primary Industries, Parks, Water and Environment (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using information or material (in part or in whole) contained on this website.

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