Cheaper olive control method shows promise

News release
18 November 2016

Feral Olive. Photo credit Biosecurity SA

Feral Olive. Photo credit Biosecurity SA

A new trial comparing control methods for Wild Olive (Olea europaea) near One Tree Hill suggests that the basal bark spraying method is more efficient than the traditional drill and fill.

The two techniques were trialled on two side-by-side plots, on olive plants of various shapes, sizes and ages (excluding seedlings).

Early results show the basal bark method to be cheaper and faster than drill and fill. The trial was carried out by Natural Resources Adelaide and Mt Lofty Ranges in collaboration with SA Water.

Using the basal bark method, 382 trees were treated at a cost of $1872, compared to 81 trees treated for $2014 using the drill and fill technique.

It took about 12 hours of labour to treat with the basal bark method, compared with 38.5 hours for drill and fill.

The trial was undertaken in February this year, and the plots were assessed in August to determine effectiveness.  

The basal bark method may take 9-12 months to completely kill the leaves on treated plants. It’s expected that by the end of this year, more than 90 per cent of olives treated by basal bark will have no green leaves left.

Previous observations suggest that a small proportion of olives treated with either method can still re-shoot in later years. Whether that proportion differs significantly between the two methods will be studied in the future.

Direct application

The use of basal bark spraying to control olives is relatively new, a technique where the herbicide is applied directly to the bark of the tree. Application is via a knapsack or hand sprayer, allowing operators to work quickly without having to carry power tools such as drills and chainsaws.

An earlier trial by AMLR in 2015 on roadside vegetation, showed that the cost of treating three-metre high olive trees with the basal bark method took 3.5 hours and cost $386, compared to 44.5 hours and $2913 for drill and fill.

The basal bark method is best applied to young and medium aged trees with smooth bark in an open woodland situation. It is not recommended as a replacement for all other techniques but provides a lower cost alternative in some situations. Depending on where olives are growing, the best results may be achieved through a combination of techniques.

Wild olives infest steeper areas of unimproved grazing land, reducing pasture productivity and providing habitat for rabbits and foxes. They are also a serious problem as they can take over native vegetation, reducing biodiversity and presenting a bushfire risk.

The basal bark method is best applied in spring or early summer, to young and medium aged trees with smooth bark. It is not recommended as a replacement for all other techniques but provides a lower cost alternative in some situations. Depending on where olives are growing, the best results may be achieved through a combination of techniques.

For how to use the technique, go to the Natural Resources Adelaide and Mt Lofty Ranges website and search for ‘basal bark’.

Or please call the Natural Resources Adelaide and Mt Lofty Ranges Galwer office on 8523 7700.

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More information

Natural Resources Adelaide and Mount Lofty Ranges