A GUIDE TO THE BIOLOGICAL CONTROL OF ALIEN INVASIVE HAKEA SPECIES

The document details the management of four invasive hakea species in South Africa, primarily silky hakea, rock hakea, sweet hakea, and willow hakea. It advocates for an integrated control strategy combining mechanical, chemical, and biological methods, with a heavy emphasis on the use of specific biological control agents—including fungi and insects—to reduce seed production and population density, especially in inaccessible mountainous terrain.

• Four hakea species were introduced from Australia to South Africa between 1835 and 1858. Silky, rock, and sweet hakea are declared category 1b weeds under NEMBA:AIS regulations, while willow hakea is a category 1b invader only in the Western Cape province.
• Silky hakea is the most widespread and serious invader, with estimated seed banks of 1.5 million seeds per hectare. Its success is attributed to high seed production, long seed lifespan, wind dispersal, and a lack of natural herbivores and pathogens.
• Mechanical control is recommended for accessible terrain and high-priority conservation areas, while biological control is the only feasible option for inaccessible mountainous areas. Chemical control using Tebuthiuron is registered only for silky and rock hakea but is generally discouraged due to costs and impacts on indigenous plants.
• The hakea gummosis fungus (Colletotrichum acutatum) is a host-specific mycoherbicide that can kill large stands of silky hakea by causing bark cankers and ring-barking the tree, though plants from the Grahamstown area are resistant.
• The hakea seed weevil (Erytenna consputa) is the most important biological control agent for silky hakea, capable of destroying more than 80% of developing seeds annually. It is less successful against rock hakea.
• The hakea seed moth (Carposina autologa) complements the seed weevil by destroying seeds in mature woody fruits that escaped the weevil's attack, reducing accumulated seeds at some sites by up to 40%.
• The hakea stem-boring beetle (Aphanasium australe) can kill plants by weakening them structurally through extensive tunneling in the base of stems and sub-surface roots, often causing trees to fall over during summer winds.
• The hakea bud weevil (Dicomada rufa) and leaf weevil (Cydmaea binotata) have limited impact; the bud weevil reduces fruit and seed production, while the leaf weevil's damage is described as negligible.
• Effective biological control requires the establishment of 'biological control reserves' (1–5ha in size, 5–10km apart) to prevent local extinction of insects during mechanical clearing and to provide sources for redistribution.
• Post-fire management is critical: gummosis fungus should be applied to seedlings in the first year, followed by the release of seed and bud weevils in years 2–5, and the seed moth once mature fruits appear in year 4+.

APA

Wood, A., Fourie, A., Krug, R., & Gordon, T. (n.d.). A GUIDE TO THE BIOLOGICAL CONTROL OF ALIEN INVASIVE HAKEA SPECIES. WWF South Africa. https://wwfafrica.awsassets.panda.org/downloads/hakea_english_flipping_book_hires.pdf

Chicago

Wood, Alan, Andries Fourie, Rainer Krug, and Tony Gordon. A GUIDE TO THE BIOLOGICAL CONTROL OF ALIEN INVASIVE HAKEA SPECIES. WWF South Africa, n.d. https://wwfafrica.awsassets.panda.org/downloads/hakea_english_flipping_book_hires.pdf.

Wikipedia

{{cite report |last1=Wood |first1=Alan |last2=Fourie |first2=Andries |last3=Krug |first3=Rainer |last4=Gordon |first4=Tony |title=A GUIDE TO THE BIOLOGICAL CONTROL OF ALIEN INVASIVE HAKEA SPECIES |publisher=WWF South Africa |url=https://wwfafrica.awsassets.panda.org/downloads/hakea_english_flipping_book_hires.pdf |access-date=17 August 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{woodndguide, author = {Wood, Alan and Fourie, Andries and Krug, Rainer and Gordon, Tony}, title = {{A GUIDE TO THE BIOLOGICAL CONTROL OF ALIEN INVASIVE HAKEA SPECIES}}, institution = {WWF South Africa}, url = {https://wwfafrica.awsassets.panda.org/downloads/hakea_english_flipping_book_hires.pdf}, urldate = {2026-08-17}, note = {Indexed by Climate Insights Directory} }