Willow infestation is likely

The sustained high water flows through the Winter months has stripped the instream vegetation of most streams and rivers and created.

The results look impressive with little or no weeds evident, however careful inspection will reveal that this not the case.

Two processes contributed to the moon scape left on these waterways, fast flowing water containing debris and the long duration of the high flows that smothered the vegetation of light and oxygen with silt.

Each mature willow that has been stripped has the potential to propagate hundreds of new trees with each brittle twig capable of being translocated in silt and debris.

Several surveys conducted by the Central Tablelands Local Lands Services have revealed the potential for a large Willow infestation this season.

Willows are listed as one of twenty Weeds of National Significance (WoNS).

This is due to their invasive nature and their impacts on the hydrology and bio-diversity of the river system. Willow control costs NSW approximately $3 million per annum.

Several factors have contributed to this potential disaster; the extensive prolonged high flows, high velocity, siltation levels above normal flow lines, no competition from other species yet to germinate, warm moist conditions, low grazing pressure from better land management and strong pasture growth.

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The inspections have revealed that where any willow twigs, branches or trunks have come to rest they have established roots and sprouted in the silt and fine debris have deposited along the watercourses.

Willows reduce habitat for native and aquatic species by being invasive along water courses and in wetlands. Dense shade over summer can reduce light levels and water temperatures which affect aquatic life.

Roots spread into stream beds reducing water flows, diverting water from the main channel and creating upstream flooding.

Leaf drop in autumn can cause organic matter contamination and reduction in oxygen levels in water.

Action is required from all land managers to stop a major Willow infestation by:

1.) Being vigilant for translocated willows along waterways.

2.) Strategic high density grazing.

3.) Pulling new Willow sprouts out of the waterways, plants less than 50cm tall are fairly easy to pull. If it breaks off at ground level then the root usually needs to be removed. The pulled material needs to be taken to a dry site to prevent it re-establishing.

4.) Foliar spraying with the appropriate chemical can be used on smaller trees, shrubs, seedling infestations or regrowth from other treatments during summer to autumn when leaves are present in close proximity to the waterway.

To control existing mature Willow infestations –

Putinjections every 10cm around the trunk or base and apply 2mL of the appropriate chemicalper cut or site.

Injection sites may be made with a tomahawk or chisel to penetrate the sapwood or a 1cm drill 2-4cm deep angled down at 45 degrees. Stem injections appear to work best in autumn just before the leaves change colour.

Trees with trunks less than 10cm diameter can be cut in Autumn and the stump immediately painted with the appropriate chemical. Tops should be moved to dry ground to prevent them taking root. Cutting alone is ineffective because the tree readily re-sprouts.

In areas where trees need to be physically removed, consider killing them with herbicides some months before removal or cut the trunk between ground level and the first branches and immediately paint the cut stump with the appropriate chemical. Remove and burn all the trees and debris to prevent stem fragments reinfesting the site.

New plants can establish from chips so if trees are to be chipped they should be chemically killed first or chipped on a dry site and inspected 1-2 years later and sprayed if necessary with the appropriate herbicide. Revisit the site every two years to remove new plants before they set seed or get too big for hand removal.

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