Selecting for Weed Resistance: Herbicide Rotation and Mixture

Abstract

Herbicide rotations and mixtures are widely recommended to manage herbicide resistance. However, little research has quantified how these practices actually affect the selection of herbicide resistance in weeds. A 4-yr experiment was conducted in western Canada from 2004 to 2007 to examine the impact of herbicide rotation and mixture in selecting for acetolactate synthase (ALS) inhibitor resistance in the annual broadleaf weed, field pennycress, co-occurring in wheat. Treatments consisted of the ALS-inhibitor herbicide, ethametsulfuron, applied in a mixture with bromoxynil/MCPA formulated herbicide (photosystem-II inhibitor/synthetic auxin), or in rotation with the non-ALS inhibitor at an ALS-inhibitor application frequency of 0, 25, 50, 75, and 100% (i.e., zero to four applications, respectively) over the 4-yr period. The field pennycress seed bank at the start of the experiment contained 5% ethametsulfuron-resistant seed. Although weed control was only marginally reduced, resistance frequency of progeny of survivors increased markedly after one ALS-inhibitor application. At the end of the experiment, the level of resistance in the seed bank was buffered by susceptible seed, increasing from 29% of recruited seedlings after one application to 85% after four applications of the ALS inhibitor. The level of resistance in the seed bank for the mixture treatment after 4 yr remained similar to that of the nontreated (weedy) control or 0% ALS-inhibitor rotation frequency treatment. The results of this study demonstrate how rapidly ALS-inhibitor resistance can evolve as a consequence of repeated application of herbicides with this site of action, and supports epidemiological information from farmer questionnaire surveys and modeling simulations that mixtures are more effective than rotations in mitigating resistance evolution through herbicide selection.

Identifying Optimum Herbicide Mixtures to Manage and Avoid Fenoxaprop-p-Ethyl Resistant Phalaris minor in Wheat

“…During this study fenoxaprop-p-ethyl was not used as a mixture component in any of the mixtures. Effective control of resistant weed populations with herbicide mixtures has been reported in previous findings (Beckie and Reboud, 2009).…”

“…The mixtures are also an effective strategy to control herbicide resistant weeds by exploring the reduced fitness of resistant weeds and due to negative cross resistance (Beckie, 2006). Partner herbicides must have different modes of action to make herbicide mixtures more efficient in delaying and preventing resistance (Friesen et al, 2000;Beckie and Reboud, 2009). Tank mixture of acetolactate synthase (ALS) herbicides with MCPA have proved very effective to manage and delay resistance development in different weed species.…”

Selectivity of clomazone and S-metolachlor applied after cassava pruning

“…The selection of other selective herbicides to cassava and that have different mechanisms of action, such as for example S-metolachlor, can contribute to the management of weeds and prevent the selection of biotypes that are resistant to the herbicides in cassava cultivation areas (Beckie, 2006;Beckie & Reboud, 2009;Mello et al, 2012;Vencill et al, 2012).…”

Growth and Development of Digitaria insularis Biotypes Susceptible and Resistant to Glyphosate

“…Selecting for herbicide-resistant weed biotypes has been usual in agricultural lands in numerous countries; management practices used in modern agriculture based on intensive use of herbicides have increasingly urged the selection of these biotypes (Beckie and Reboud 2009;Vencill et al, 2012).…”