This paper explores the role of regulation and legislation on influencing the development and diffusion of technologies and methods of crop production. To do this, the change in pesticide registration under European Regulation 1107/2009 ‘Placing Plant Protection Products on the Market’ was followed through the UK’s agricultural system of innovation. Fieldwork included: a series of interviews conducted with scientists, agronomists and industry organisations; a programme of visiting agricultural events; as well as sending an electronic survey to British potato growers. The (...) innovation system is noted to have made the legislation less restrictive than originally proposed. The most notable system response to the legislation is the adjustment of agrochemical company pesticide discovery strategy and their expansion into biologically derived treatments. There have also been other innovation responses: agricultural seed companies have been breeding in pathogen resistance in their cultivars; agricultural consultancies are prepared to recommend pathogen-resistant seeds; scientists are using the change as justification for adopting their solutions; the agricultural levy boards funded research into off-label pesticide uses; and producers, potato growers in particular, have been seeking advice, but not changing their growing practices. (shrink)