Herbicide mixtures for control of herbicide resistant Apera spica-venti populations

Apera spica-venti is a very important weed in cereal crops throughout Central, Northern and Eastern Europe and herbicide resistance to post-emergence herbicides is often present in A. spica-venti populations. To improve herbicide efficacy and to prevent further spread of resistance, herbicide mixtures with different mode of action might be a solution. The aim of this study was to investigate potential interactions of ALS- and ACCase inhibiting herbicides on different A. spica-venti populations. Mixtures of pinoxaden with met- and thifensulfuron caused antagonism in herbicide performance to all populations tested. Tank mixtures of pinoxaden with flora- and pyroxsulam showed different interactions according to the status of resistance of the tested populations. Populations susceptible to both herbicides showed additive effects indicating that herbicides in the mixture do not influence their respective efficacy. Resistant populations showed not necessarily the same reaction to this herbicide mixture. In target-site resistant populations the efficacy of mixtures was increased with higher portions of the active ingredient still effective on the population. For populations with non-target-site resistance mechanisms the reaction was unpredictable depending on the population and mixture ratio. Synergism, antagonism and additive effects could be observed. However, results showed that these effects cannot be predicted even within different mixtures from the same modes of action.