Willows

What are willows?

• Willows are a serious environmental weed.
  

• Willows are a declared weed in Tasmania under the Tasmanian Biosecurity Act 2019 and associated Regulations. The importation, sale and distribution of willows are prohibited in Tasmania.

• Willows are also a Weed of National Significance (WONS).
  

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.