The relationship between herbicide resistance and the use of integrated weed management: Is it simply reactive?

Herbicide resistance (HR) has been a major management challenge and ongoing threat in cropping regions over several decades, particularly in the time since the widespread adoption of no-tillage cropping systems. Despite extensive and severe development of resistance in Australian cropping regions, growers have been able to maintain control of new weed populations by introducing new herbicides and non-herbicide practices. These integrated weed management (IWM) practices have helped farming systems maintain productivity and adapt to changing environmental and agronomic conditions. Earlier studies found that the adoption of these alternative practices was associated with a reaction to the initial development of forms of HR on a farm. Practices include those classified as harvest weed seed control (HWSC) that kill potentially herbicide resistant weed seeds and reduce overall weed seedbank populations without increasing HR selection pressure. A largely unexplored aspect of the socioeconomics of HR management is whether the initial ‘reactive’ adoption of IWM has a ‘preventative’ effect on the further spread or proliferation of resistance development to other herbicides and in other weed species. To gain a deeper understanding of the farm-scale factors determining the presence of HR, the adoption of IWM practices, and the relationship between IWM use and HR status, we focus on whether initial reactive adoption of IWM has a preventative effect on further resistance development. Data from 602 broadacre grain growers across 13 agroecological zones of Australia were analyzed using Ordinary Least Squares and Logistic regressions to assess the extent of IWM practice adoption, while Ordered Logit models were used to capture the diversity of IWM practice use, including HWSC strategies. Notably, we found that adoption of IWM (including HWSC) was higher in the Western and Southern regions, most likely where HWSC practices can offer greater control on the most common resistant weed types, such as annual ryegrass. There was no evidence to support the argument that IWM use on farms is associated with reduced herbicide use, but there was considerable evidence to show that early forms of HR development on farms have led to the use of IWM practices, such as HWSC, that have the potential to reduce the seed set of weeds with potential new forms of resistance. The extent of HR was the only consistently highly significant variable to explain IWM use. These results have the capacity to pre-emptively identify sustainable weed management scenarios in various regional farming systems and future contexts, including where earlier ‘reactive’ adoption of resistance management practices may now be offering ‘proactive’ benefits. • Examine farm-scale factors influencing IWM and HWSC in Australian cropping systems. • First nationwide farm-level study links HR presence to proactive adoption of IWM practices. • Analysis of 602 growers' data across 13 AEZ using OLS, logistic, and ordered logit models. • HR presence, farm size, no-till years, and advisory support strongly drive IWM uptake, especially in WA & SA. • Evidence-based guidance for regional policymakers to target HR management and support IWM adoption.