Striking back at weedy Blackwood

IT’S a tree that most of us wouldn’t recognise – but Nature Conservation Margaret River Region says Blackwood is a weedy wattle that should be removed from gardens and bush blocks because it’s such a big threat to biodiversity and harder than most to control.

As part of a two-year campaign, Nature Conservation has been putting the spotlight on the worst weedy trees in the region and helping people to identify and remove them. Most of these are species that hail from the eastern states and become rampant here without their natural controls including Victorian Teatree, Sweet Pittosporum, Sydney Golden Wattle and Flinders Range Wattle.

Now, Blackwood (Acacia melanoxylon) is in the crosshairs of the conservation group. It says everyone from suburban gardeners to rural property owners should be aware of this “woody weed” and help to stop the spread.

Nature Conservation’s Biodiversity Officer Mike Griffiths said Blackwood is a large, slender tree that can grow to more than 20 m tall, with smooth grey bark and deep green foliage. Its cream-coloured flowers in spring make it easy to distinguish from most other tree wattles which typically have deep gold or yellow flowers. Their clusters of curly, twisted seed pods also make it distinctive from other wattles.

“Native to eastern Australia, Blackwood was historically planted here as windbreaks and shade trees, even in plantations for timber, but it’s now spreading into forests throughout the southwest. And one unusual feature makes it especially bad as an invasive species – it suckers and sends out thickets of young plants via special roots.  On top of that, the seed can last for many years in the soil. It favours damp valleys and creek lines where it spreads quickly and grows fast, and in time, forms dense, almost impenetrable thickets, shading out native shrubs, outcompeting native trees and degrading habitat for our special native animals.”

Blackwood control must be done with extra care. Stem-injecting or painting freshly cut stumps with herbicide is especially important because of its tendency to put out extra growth if disturbed and not poisoned. Trees up to 20 cm diameter can also be controlled by basal bark painting with herbicide and diesel. Small plants close to older trees are typically attached by suckering roots and must be poisoned or re-shoot profusely when disturbed.  Hand-pulling is only effective with young plants that have grown from seed but look very similar to suckering plants.

“We really want everyone to recognise Blackwood and help stop the spread,” Mr Griffiths said. “They’re harder than a lot of woody weeds to control, and bigger jobs may need qualified contractors or the Nature Conservation on-ground team, but it’s worth it when you think of how much you’re helping the surrounding bushland.  We don’t want to see more creek lines and valleys choked by thickets of these highly invasive trees in another 10 or 20 years.  If you have any woody weeds on your property, we really encourage you to remove them because one tree can spread seed over a large area in just a few years. Instead, replace them with local natives, which boost our bushland and are beneficial for wildlife.”

To learn more, watch a comprehensive Blackwood identification and removal video HERE, Or drop in to the Nature Conservation office and pick up a free woody weed booklet which details identification features and control measures.

The Woody Weeds Campaign is funded by the Western Australian Government’s State Natural Resource Management Program, and includes funding on a 50-50 cost sharing basis for landholders located in selected areas close to high priority bushland, reserves or national parks. To enquire about grant funding, email [email protected] or see www.natureconservation.org.au for more information.

Blackwood