Ecological fitness of herbicide-resistant weeds

Prevention and management of herbicide resistance require adopting practices that reduce selection pressures favouring resistant plants. This goal requires understanding evolution and dynamics of resistant populations. In triazine-resistant weeds, a target site mutation impairs normal function, resulting in reduced fitness relative to susceptible plants. However, in the field, selection occurs for traits unrelated to resistance which may reduce detrimental effects of resistance. In cases of resistance to other herbicides, other effects associated with resistance seem to be of little practical significance in the field. In these cases, agricultural practices may be more important in determining population dynamics than fitness effects of the resistance mutation. While herbicide resistance does not necessarily incur a cost to fitness in the field, insufficient data are available to generalise about this relationship. The impact of herbicide resistance on fitness must be evaluated on a case-by-case basis for weed biotypes in the environment where they occur.