Commercial Olive Plantations are part of the agricultural sector in north-east Vicotira producing a variety of edible fruit and styles of oil, but did you know that Olives can be a serious environmental weed?
Think twice if you are thinking of planting olives in your garden or on your property for ornamental purposes. And if you already do have olives growing make sure you harvest all the fruit before the birds get to them.
That’s the message those involved in the Indigo Feral Olive Control Program would like to get out to the wider community.
While olives are an important part of the agricultural and tourist industry in north-east Victoria, they have a “dark” side.
A hardy plant, well-suited to our climate, mature olive trees produce large quantities of fruit with seeds easily dispersed by birds. As a result feral olives have become a serious environmental weed and pose a real threat to remnant native vegetation.
A long-lived species (100 years or more), olives produce a dense canopy that effectively shades out native plants and suppresses natural regeneration. A South Australian study found native Eucalypt woodlands infested with olives have a 50% reduction in plant diversity and an 80% reduction in native plant canopy cover.
There are olive infestations in many parts of south east Australia including major infestations in the Adelaide Hills in South Australia and the Mt Annan Botanic Gardens in the Blue Mountains, NSW. A declared weed in NSW and South Australia, olives are not yet officially a weed in Victoria.
The Indigo Feral Olive Control Program is an ambitious joint project by the Rutherglen and Chiltern Landcare groups in Victoria’s North-East which has seen more than 400km of roadsides in the Indigo Shire mapped and cleared of feral olive trees.
The groups’ goals are to remove the olives before they do  became a major environmental weed and inform the community of the potential threat to the district’s remnant vegetation along roadsides, on private properties and in state and national parks.
The three year program, which began in May 2012, received $96,000 funding from the Victorian Sate Government’s Communities for Nature program.  As well Indigo Shire is actively supporting the project and has contributed $10,000 for removing other woody weeds on selected roadsides.
“From Indigo Shire’s perspective this project is viewed as a really pro-active program rather than a reactive one,” says Jenny Pena, the Shire’s Natural Resources Management Officer. “The landcare groups are trying to tackle an issue before it gets too big. It complements our own weed program and we can complement theirs.”
But for the program to be successful, the source of olive infestations also needs to be tackled.
“There is a real concern that garden plantings and farm driveway plantings of olives are possibly a ticking time-bomb unless those olives are well-managed and regularly pruned,” says Jenny Davidson, president of the Rutherglen Landcare Group and convenor of the program’s steering committee.  
“Ensuring we don’t allow our olives to become an environmental weed is very much a community responsibility. We need to be very aware of what we are planting in our gardens and on our properties.”
Instead of planting fruiting olives, the suggestion is to plant a non-fruiting variety such as the Swan Hill Olive, or a native species with similar foliage and growth characteristics e.g. Western Rosewood (Alectryon oleifolium subs.canescens)
 Those involved are also hoping that raising people’s awareness of the environmental threat that olives can pose will encourage landholders to remove unwanted  and feral olives on their properties and adjacent roadsides.
The initiative isn’t targeting commercial olive growers.
“Properly managed olives are OK because you are removing the fruit and the seed source,” says project manager Rick James, from Riparian Management Services.
“If you are a conscientious professional olive grower you should be aware they can become a weed and remove the fruit. It would be good practice for growers to monitor their immediate area and remove any seedlings that do pop up on nearby roadsides or reserves.”
*Members of the project are happy to talk to other landcare groups and agencies and share their experiences about what they have learnt from undertaking the project and have developed a fact sheet “Olives: friend or foe?”