Weed resistance

Herbicide resistant plants are those with the inherited ability […] to survive and reproduce following exposure to a dose of herbicide normally lethal to the wild type. (Weed Science Society of America)
Cross resistance: resistance to different more than one herbicide but only a single MoA
Multiple resistance: resistance to more than one MoA and several herbicides

Herbicide resistance can occur naturally. An alteration in the genome leads to the resistance of individual plants to a certain mode of action. Two main types of resistance are differentiated: Target site resistance and metabolic resistance

Resistance mechanisms

Target-site resistance

Alteration of a single amino acid
Specific to one mode of action

Herbicide cannot bind to the target site
Increased herbicide dose not increase control

Metabolic resistance

Enhanced capacity to metabolise the herbicide
Not specific to one mode of action

Inactivation before the herbicide can reach the site of action
Increased herbicide dose help to increase control

Target-site resistance

Metabolic resistance

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Selection pressure

Increased selection pressure, e.g. using the same active ingredients or mode of action too often, can lead to a herbicide weed resistance over time. Within a crop rotation several measures are available to reduce this risk proactively.