Olea Europaea (Olive) Management Information

Olea europaea (olive) Management Information

Prepared by the IUCN SSC Invasive Species Specialist Group

Contents 1.0 Introduction...... Page 1 2.0 Preventative Measures...... Page 1 3.0 Monitoring...... Page 2 4.0 Physical Control...... Page 3 5.0 Chemical Control ...... Page 3 6.0 Biological Control...... Page 5 7.0 References...... Page 5

1.0 Introduction Olea europaea is a long-lived tree that ranges in height from 8 – 15 m, depending on environmental conditions (Parsons & Cuthbertson, 1992; Martin, 2003). While it is capable of persisting in most environments, O. europaea is most prolific in semi-arid to sub-humid warm- temperate regions (Parsons & Cuthbertson 1992), in sandy loam soil of moderate depth (Spennemann & Allen, 2000).

Olea europaea subsp. europaea has been cultivated around the world for thousands of years, not only for its edible fruit and the production of oil, but also as an occasional ornamental and shade species (Martin, 2003; Starr et al., 2003b). While of less economic importance O. europaea subsp. cuspidata (also known as O. e. africana) has also been widely cultivated in some areas such as Hawaii and Australia as a wind break and hedge species as well as a source of timber and for erosion control (Starr et al., 2003a).

Both subspecies have been known to escape from cultivation primarily through the high production of bird and mammal dispersed seeds (Spennemann & Allen, 2000) where they are capable of forming a dense canopy which shades out native species while still allowing conspecific seedlings to establish. The result of this is the formation of dense monocultures, capable of altering ecosystems and habitats through the loss of native biodiversity (Cuneo & Leishman, 2006).

The control of O. europaea is generally labour intensive due to the large amount of seed produced and its coppicing ability (Spennemann & Allen, 2000). Follow up operations are therefore to be recommended and care must be taken to avoid the dispersal of seed and fruit during control operations (Spennemann & Allen, 2000). These control methods are described as most effective in spring or summer in Australia (Spennemann & Allen, 2000) and are described in more detail below.

2.0 Preventative Measures A Risk Assessment of O. europaea for Hawaii and other Pacific islands was prepared by Dr. Curtis Daehler (UH Botany) with funding from the Kaulunani Urban Forestry Program and US Forest Service. The alien plant screening system is derived from Pheloung et al. (1999) with minor modifications for use in Pacific islands (Daehler et al., 2004). The result is a score 2 of 5 and a recommendation of: "The species has been assessed using the WRA system; however, no assessment of risk can be provided at this time because 1) crucial information is missing from the assessment or 2) the species possesses a combination of traits and characteristics that make its likely behaviour difficult to assess using the WRA system."

The same Risk Assessment for Australia was prepared by David Cooke in 2001 with a score of 2 and the same recommendations. In Australia O. e. cuspidata has been declared a Class 4 noxious weed under Section 7 of the New South Wales Noxious Weeds Act 1993 for the Ryde (Local Government Area) LGA where its growth and spread must be controlled according to the measures specified in a management plan published by the local control authority. Furthermore, the plant may not be sold, propagated or knowingly distributed (NSW DPI, 2006; in Cuneo & Leishman, 2006). Olea europaea (including all subspecies) is also listed as a Class 5d weed under the South Australia Natural Resources Management Act 2004, stating that the landowner must control and keep controlled all plants of that class on the owned land and may be liable for the cost of adjacent roadside weed control measures (Parliament of South Australia, 2004; in Cuneo & Leishman, 2006).

A number of cultural preventative measures have been developed by the Tasmanian Feral Olive Working Group following a resurgence in the olive industry experienced in Australia in the 1990s (Holding, 2004). These include the creation of a voluntary olive register to track to size, growth and distribution of the industry while storing information on age, location, numbers and variety into a database to determine whether groves are in proximity to susceptible vegetation (Holding, 2004). A code of practice was also developed for the olive industry aiming to help managers reduce the risk of O. e. europaea escaping from cultivation and includes wildlife monitoring and management, seedling surveillance in the bush and on roadsides, thorough harvest, and planning for abandoned groves (Holding, 2004). Each grove was also assessed for potential weed risk, providing growers with the ability to gauge the potential weed risk of their groves and improving their management and surveillance (Holding, 2004). Finally, education efforts have been focussed on both commercial growers and home gardeners to increase awareness of the weed status of O. e. europaea in other parts of Australia and measures that can be taken to reduce the risk of escape (Holding, 2004).

In New Zealand, O. europaea is listed as a "Research Organism" in the Auckland Regional Pest Management Strategy 2007 - 2010. As such it is not legally recognised as a pest species, with more research needed into its impacts and limiting the spread from cultivated specimens to natural habitats (Auckland Regional Council, 2007).

As of 2003, O. europaea is still widely available for purchase in Hawaii despite its recognised invasive tendencies (Starr et al., 2003a).

3.0 Monitoring On Raoul Island, detection of invasive plant species including O. e. cuspidata was carried out through grid searching accessible areas (West, 2002). Aerial surveillance using helicopters was also used to detect more visually distinct species such as O. e. cuspidata (West, 2002). The landscape distribution of O. e. cuspidata in southwest Sydney, Australia was able to be mapped by Cuneo et al. (2009) using satellite imagery; the primary data source in this case being Landsat 7 Enhanced Thematic Mapper (ETM). Multispectral satellite imagery such as Landsat ETM has moderate spatial resolution (25 m pixel size) and large area coverage, with each image covering 185 km x 172 km, making it highly cost-effective (Cuneo et al., 2009).

ERDAS® Imagine 8.4 software was used to classify the land covers of O. e. cuspidata and other major vegetation types using a technique known as “supervised classification” in which areas of known vegetation cover type are matched onto the image to define the spectral signature for each (Cuneo et al., 2009).

This data was used to identify 1907 ha of O. e. cuspidata infestation in southwest Sydney and to quantify the conservation threat to several Endangered Ecological Communities by total area occupied (Cuneo et al., 2009).

4.0 Physical Control Hand pulling of O. europaea seedlings and small plants has been found to be effective for both subspecies (Spennemann & Allen, 2000; Starr et al., 2003a; 2003b; Department of Conservation, 2010), and is encouraged over herbicide spraying for isolated patches (Spennemann & Allen, 2000). Slashing established seedlings or cutting down mature individuals has no lasting effect at all due to rapid resprouting (Spennemann & Allen, 2000). Cut trees have been known to reach 1 – 2 m high within 20 months of cutting (Dellow et al., 1987; in Spennemann & Allen, 2000).

Mulching using a drum mulcher attached to an excavator has been used successfully for large scale mature infestations of O. e. cuspidata in Australia where there is sufficient access and a low erosion risk (Cuneo & Leishman, 2006). It is reportedly highly effective provided that trees and seedlings are treated with herbicide prior to mulching (Cuneo & Leishman, 2006).

Although it does not kill larger individuals, burning at low intensity was tested as a control method for small O. e. cuspidata shrubs and seedlings in western Sydney (von Richter et al., 2005). While the majority of plants smaller than 20 mm diameter were killed, results may have been confounded by a lower than average annual rainfall rate for the previous three years, increasing the effectiveness of the fire by reducing the ability for seedlings to resprout due to water stress (von Richter et al., 2005). The data collected by von Richter et al. (2005) are consistent with assertions that burning at 10 year intervals can control smaller O. e. cuspidata plants, however frequent burning could also compromise the conservation of any native species also present. Larger individuals would also need to be removed through other means (von Richter, et al., 2005).

The reduction of grazing is thought to be a significant factor in the spread of O. e. cuspidata in New South Wales (Cuneo & Leishman, 2006). While systematic grazing of roadside edges and land adjacent to plantations would reduce the survival of seedlings, if already firmly established, smaller leaves near the stem are produced which are not fed upon thus ensuring its survival (Dellow et al., 1987; in Spennemann & Allen, 2000). While continued heavy grazing may contain the spread of O. europaea, like burning it is also environmentally undesirable (Spennemann & Allen, 2000).

5.0 Chemical Control A variety of herbicides have been found to be effective for different application techniques against O. europaea. For foliar spraying applications, Santos et al. (1992) tested 5% aqueous solutions of Roundup (glyphosate), Garlon 4 (triclopyr) and Tordon 22k (picloram) on 60 O. e. cuspidata shrubs ranging in height from 85 – 165 cm (34 – 65 in.) in Hawaii. The most effective herbicide in this case was found to be Garlon 4, with 87% of treated plants showing severely desiccated foliage after one month and a 100% mortality rate after 8 months (Santo et al., 1992). The least effective herbicide used in foliar spraying was Tordon 22k which showed <50% of treated leaves being chlorotic after a month with little difference when surveyed at 12 months (Santos et al., 1992). Spennemann & Allen (2000) also suggest foliar spraying of O. europaea with a triclopyr based herbicide but that more mature trees require cutting before application while the Department of Conservation (2010) suggest spraying O. e. cuspidata with a metsulfuron-methyl based herbicide (600 g / kg at 5 g / 10 L).

Additionally, basal bark spraying using a triclopyr and diesel mixture (1:14) was reported to be a simple and effective application for the control of O. europaea regardless of size; this technique involves spraying the first 30 cm of the trunk, wetting the bark to runoff point (Dellow et al., 1987; in Cuneo & Leishman, 2006).

For the spraying of O. e. cuspidata seedlings, trials by Santos et al. (1992) using 5% and 1% solutions of the same herbicides, with the addition of Amitrol T (amitrol), again showed that 5% Garlon 4 was the most effective, resulting in 100 % control in all test plots after 4 months. 1% Garlon 4 was the second most effective and consistent achieving 75 – 90% mortality in all plots by the 4th month. While the 5% solutions of the other herbicides tested were always more effective than the 1% solutions, they were not shown to be effective (Santos et al., 1992). In contrast, Spennemann & Allen (2000) and Cuneo & Leishmann (2006) suggest spot-spraying of O. europaea seedlings and coppice-shoots with glyphosate. Seedlings up to 6 months old are known to not resprout after such a treatment (Spennemann & Allen, 2000).

Spennemann & Allen (2000) state that broadscale application of triclopyr kills most other plants and can have serious environmental side effects; sufficient planning and care should therefore be put into its use. Santos et al. (1992) state that while the triclopyr based herbicide Garlon 4 was the most effective treatment in spraying both seedlings and shrubs, more research is needed to find the lowest effective concentration to minimise cost and potential hazards to native vegetation and the applicator. While Santos et al. (1992) found limited environmental side- effects when using Garlon 4, they recommend only spraying in situations when the targets are less than 1 m tall and where native plants are not in close proximity.

As mentioned earlier, more mature trees require cutting before herbicide application onto cut surfaces (Spennemann & Allen, 2000). Santos et al. (1992) trialled 14 different treatments on 350 O. e. cuspidata shrubs of five different size classes including Tordon RTU (picloram) undiluted, Tordon 22K and Roundup undiluted and as 20% and 5% dilutions in water and Garlon 4 undiluted and as 20%, 10%, 5%, and 2% dilutions in diesel oil. Each treated individual was cut as close to the ground as possible using a chainsaw (usually less than 15 cm or 6 in.) and then immediately treated with the herbicide. Control effectiveness was not found to vary among the five size classes with Tordon RTU and undiluted Garlon 4 being the most effective treatments, neither of which resulted in the stump successfully resprouting and with cambium vigour checks showing that all treated stumps were completely dead at 6 and 12 months for each respective treatment (Santos et al., 1992). Also effective, albeit to a lesser degree, were undiluted Tordon 22k and Roundup, as well as the 20% Garlon 4 in diesel oil treatment; the two undiluted treatments resulted in 12% of the stumps resprouting after 12 months while the Garlon 4 treatments resulted in 20% of the stumps resprouting after 12 months (Santos et al., 1992). Undiluted glyphosate and a 25 % triclopyr in diesel mixture are similarly recommended by Cuneo & Leishman (2006). Due to Tordon RTU being cheaper to apply and presenting a lower hazard to the applicator, it is recommended by Santos et al. (1992) as the preferred treatment on cut stumps of O. e. cuspidata.

Similarly, Motooka et al., (2003), state that large O. europaea specimens (subspecies not stated) can be injured by cut surface applications of triclopyr, glyphosate and 2, 4-D (2, 4- Dichlorophenoxyacetic acid) in descending order of severity. Concentrations are not specified however and the kill rates were reportedly low at 12 months after treatment. The Department of Conservation (2010) also suggest the use of metsulfuron methyl (600g / kg at 5g / L) for cut stump applications for O. e. cuspidata as well as a cut and squirt technique making one cut every 100 mm around the trunk and then applying metsulfuron-methyl (600 g / kg undiluted) to each cut.

Cuneo & Leishman (2006) report that using a portable drill to drill 3 cm deep holes in the trunk, 4 cm apart at 45 degree angles and then injecting undiluted glyphosate (360 g / L, 2.5 ml per hole) is commonly used to control O. e. cuspidata in inaccessible areas where cutting and removing is not practical. Alternatively, a chisel can be used to create regularly spaced openings in the trunk in a technique known as frilling (Cuneo & Leishman, 2006).

Soil applications of hexazinone and tebuthiuron have been shown to be ineffective against mature plants (Motooka et al., 2003).

6.0 Biological Control While there are no known biological control agents being used against O. europaea at present, the Olive Lace Bug (Frogattia olivinia) is native to parts of Australia and is known as a pest of O. e. europaea, causing small fruits on heavily infected trees to drop before ripening (Robertson, 2005; in Cuneo & Leishman, 2006). Frogattia olivinia however is not noted to impact on O. e. cuspidata requiring further research to determine if a level of biological control for this subspecies can be provided (Cuneo & Leishman, 2006). Biological control of naturalised populations is not possible without also harming the fruit industry (Spennemann & Allen, 2000) with any move to introduce a biological control agent likely to encounter strong industry resistance (Cuneo & Leishman, 2006).

7.0 References 1. Cuneo P., & Leishman, M.R. (2006). African Olive (Olea europaea subsp. cuspidata) as an environmental weed in eastern Australia: a review. Cunninghamia, 9, 545-577. 2. Department of Conservation (DOC). (2010). Weedbusters Olea europeaea subspecies cuspidata. Retrieved April 3, 2010 from Department of Conservation website: http://weedbusters.co.nz/weed_info/detail.asp?WeedID=68 3. Holding, D. (2004). European olive in Tasmania factsheet. Cooperative Research Centre for Australian Weed Management. 4. Martin, G.C., (2003). Olea europaea L. olive. Retrieved April 3, 2010 from USDA Forest Service website: http://nsl.fs.fed.us/wpsm/Olea.pdf 5. Motooka, P., Castro, L., Nelson, D., Nagai, G., & Ching, L. (2003). Weeds of Hawaii’s Pastures and Natural Areas; An Identification and Management Guide. College of Tropical Agriculture and Human Resources, University of Hawai’i. 6. Parsons, W.T., & Cuthberson, E.G. (1992). Noxious weeds of Australia. Inkata Press: Australia. 7. Spenneman, D.H.R., & Allen, L.R. (2000). Feral olives (Olea europaea) as future woody weeds in Australia: a review. Australian Journal of Experimental Agriculture, 40, 889- 901. 8. Starr, F., Starr, K., & Loope, L. (2003a). Olea europaea subsp. cuspidata African olive Oleaceae. Retrieved April 3, 2010 from Hawaiian Ecosystems at Risk (HEAR) website: http://www.hear.org/Pier/pdf/pohreports/olea_europaea_subsp_cuspidata.pdf 9. Starr, F., Starr, K., & Loope, L. (2003b). Olea europaea subsp. europaea European olive Oleaceae. Retrieved April 3, 2010 from Hawaiian Ecosystems at Risk (HEAR) website: http://www.hear.org/pier/pdf/pohreports/olea_europaea_subsp_europaea.pdf 10. von Richter, L., Little, D., & Benson, D.H. (2005). Effects of low intensity fire on the resprouting of the weed African Olive (Olea europaea subsp. cuspidata) in Cumberland Plain Woodland, Western Sydney. Ecological Management and Restoration, 6, 230-232. 11. West, C.J. (2002). The eradication of alien plants on Raoul Island, Kermadec Islands, New Zealand. In: C.R. Veitch & M.N. Clout (Eds.), Turning the Tide: The Eradication of Invasive Species. Proceedings of the International Conference of Eradication of Island Invasives. Occasional Paper of the IUCN Species Survival Commission, No. 27.