A GUIDE TO THE BIOLOGICAL CONTROL OF ALIEN INVASIVE HAKEA SPECIES

This guide provides technical instructions for the biological control of alien invasive hakea species in South Africa, specifically focusing on silky, rock, sweet, and willow hakea. It details the use of various biological control agents—including fungi and insects—and explains how to integrate these with mechanical and chemical control methods to manage infestations in mountain catchments.

• Four hakea species were introduced from Australia to South Africa between 1835 and 1858. Silky hakea (Hakea sericea), rock hakea (Hakea gibbosa), and sweet hakea (Hakea drupacea) are declared category 1b weeds. Willow hakea (Hakea salicifolia) is a category 1b invader only in the Western Cape province.
• Silky hakea is the most widespread and serious invader, with recorded invasion areas growing from 9,000ha in 1939 to 360,000ha by 1983. Its success is attributed to high seed production, long seed lifespan, wind dispersal, and a lack of natural herbivores and pathogens.
• Control strategies are categorized by accessibility: mechanical control is recommended for accessible areas, biological control for inaccessible areas, and an integrated approach for areas that are difficult to access. Chemical control using Tebuthiuron is registered only for silky and rock hakea but is generally discouraged due to costs and negative impacts on indigenous plants.
• The hakea gummosis fungus (Colletotrichum acutatum) is a host-specific mycoherbicide used against silky hakea. It causes bark cankers and gummosis, which can kill the plant by girdling the stem. It is applied via wound-treatment of stems (≥2cm diameter) or as a bran inoculum for seedlings.
• 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 also used for rock hakea, though with less success.
• The hakea seed moth (Carposina autologa) complements the seed weevil by destroying seeds in mature, woody fruits that escaped weevil attack. It has reduced accumulated seeds at some sites by up to 40% over several years.
• 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 strong summer winds.
• Other biological agents include the hakea bud weevil (Dicomada rufa), which reduces seed production by feeding on flower buds, and the hakea leaf weevil (Cydmaea binotata), which causes negligible damage by tunneling through succulent leaves and stems.
• Biological control reserves of 1–5ha, spaced 5–10km apart, should be established in areas undergoing mechanical clearing. These reserves act as breeding grounds to prevent local extinction of insect agents and serve as sources for redistribution.
• Post-fire implementation is critical: gummosis fungus should be applied to seedlings immediately after the first rains, followed by the release of seed and bud weevils in years 2–5, and the seed moth once mature fruits appear (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} }