Monitoring & Mitigation

Here’s how weed scientists monitor herbicide resistance and develop systems to mitigate the development and spread of resistant weeds.

Monitoring and mitigation is an important aspect of managing herbicide resistance in weeds. Detecting resistance early, understanding its scope in an area and limiting the spread are all important steps in managing the risk.


Public and private weed scientists monitor herbicide-resistant weed populations for early detection and to monitor the scope of the problem.

Monitoring methods include:

●      Field surveys, where seeds are collected and tested using bioassays;

●      Market research surveys of farmers and weed scientists;

●      Tracking herbicide performance complaints.

Monitoring programs vary depending if the monitoring is reactive or proactive. Both have different goals, challenges and levels of success. See more detailed examples in the full text of the paper.


Identifying herbicide resistance early is difficult. Through the first few years of selection, resistant weeds only make up a small proportion of the total weed populations. These ‘escapes’ may be mistaken for weather, application or herbicide performance issues. The question of resistance may not arise until 30-40% of the population is resistant. At that point a complaint on performance by the farmer might be the first step in identifying a resistant population and developing a plan to mitigate the issue.

Differences in monitoring

While the objectives of monitoring herbicide resistance are similar to insecticide and fungicide resistance monitoring, enough issues exist to make monitoring approaches different. Differences in insect/disease mobility, the time between generations and how resistance genes are inherited mean monitoring systems are also different.

Mitigating resistance development

When resistant weed populations are detected, steps can be taken to reduce the impact that resistance has. With weed seed bank dynamics and seed dormancy, eradication is generally not feasible. Mitigation focuses on preventing further spread and development.

Successful mitigation typically relies on education, training and the implementation of Best Management Practices (BMPs).

Download our report Monitoring and Mitigation of Herbicide Resistance: Global Herbicide Resistance Committee (HRAC) Perspectives for more information.