Weed Biological Control: Challenges and Opportunities

Michael D. Day1 and Arne B. R. Witt

Keywords:

benefit: cost ratios, host specificity, low-risk, integrated control, biological weed control

Abstract:

Biological control of weeds has been conducted since 1902, resulting in over 500 biological control agents being intentionally released against nearly 200 weed species in over 90 countries. Collectively, 15 countries in Asia and 17 of the 22 countries and territories in the Pacific region have intentionally released over 80 biological control agents to help manage over 30 of their most invasive weeds. Many of these programmes, have been highly successful. In fact, globally, over a third of all weed biological control programmes have resulted in some form of control of the target weed, resulting in huge benefit: cost ratios of up to 4,000:1. In addition, there have been very few (<1%) unpredicted, sustained non-target impacts on native or economic plants by weed biological control agents. This is because biological control agents have co-evolved with their host plants and are thoroughly tested, sometimes collectively across numerous countries, against up to 280 plant species, before being released. Moreover, many biological control agents that have proved to be successful in one country have now been released in over 30 countries, with no recorded non-target impacts. Yet, despite these successes, many countries are still reluctant to implement weed biological control. Even countries that have had tremendous successes with weed biological control in the past have shied away from implementing biological control in recent times, stating that it is too risky or doesn’t work. Unfounded and unscientific statements such as “biological control agents could evolve or mutate to attack other plant species” or “climate change may affect their host range” are often used to justify not implementing biological control. As a result, landowners continue to spend millions of dollars to purchase and apply herbicides, when an integrated approach, which includes biological control, can reduce management costs and enhance control. The challenge, therefore, is to educate all stakeholders, including communities, in the safety and cost-effectiveness of weed biological control. There are numerous opportunities to introduce highly specific and very effective biological control agents from countries where they are being utilized successfully, into other countries where the target weed is problematic to help manage these species.