Biological control of ragwort in the New Zealand dairy sector: an ex-post economic analysis

Abstract

ABSTRACTRagwort flea beetle, released in New Zealand in 1983, successfully controls ragwort, except in regions that receive very high rainfall such as the West Coast of South Island. If biocontrol had not been instigated, expenditure on ragwort control across New Zealand dairy farms in 2015 would have been an estimated NZ$64 million (adjusted for inflation and national herd size). Data on the impact of the flea beetle were used to estimate the national benefit from reduced control costs to dairy farms from biocontrol which, in 2015, was NZ$44 million. Ragwort biocontrol in New Zealand was attempted from 1926, and a net present value (NPV) analysis gave a 14:1 benefit:cost ratio, which remained positive in robust sensitivity testing. In New Zealand, the flea beetle was rejected as a biocontrol agent in 1933 on anecdotal evidence of its low impact on ragwort. This poor decision cost the dairy industry NZ$8.6 billion (NPV) from 1945 to 1999.