Although herbicides will continue to dominate weed-control practices because of their economic utility, the sustainability of herbicide use depends on their diversification and integration with nonchemical weed-control strategies. Only by implementing diverse weed-management practices will herbicides be conserved as a valuable agricultural resource.
Although a number of factors determine the frequency of resistance in weed populations, reported incidents strongly suggest that the single-most important factor leading to the evolution of herbicide resistance is overreliance on a single herbicide (or group of herbicides with the same SOA) without using other weed management options.
Herbicide use without careful thought and understanding may result in the loss of herbicide options for all farmers, especially if resistance spreads rapidly across a region. Judicious herbicide use is critical to the long-term availability of herbicides.
What herbicides should you use? It all depends on the weeds you’re trying to control. Finding the right match is important. Get it wrong and you could reduce efficacy, increase production costs and reduce your yields.
Before you start herbicide selection, it’s important to know your weeds.
Several factors increase the frequency of herbicide resistance:
- Characteristics of the herbicide and herbicide class
- Weed biology
- Cultural practices, such as crop rotation, tillage practices, and time of planting, all play a role in determining the likelihood and frequency of herbicide resistance.
Resistance to herbicides is a function of:
- Frequency of use
- How the herbicide has been used
- The herbicide characteristics
- Resistance mechanism in the weed
Herbicides are classified in many ways:
- By crop
- By application timing
- By Mode of Action (MOA) and Site of Action (SOA)
Mode of Action vs. Site of Action
The distinction between Mode of Action and Site of Action relates to “how” the herbicide works vs. “where” it works. For example, one mode of action works to destroy chlorophyll in the presence of light. However, different herbicides can do that by blocking different enzymes, or sites, in the plant’s physiology. Each represents a site of action that takes a different path to achieve the same result. Therefore, using multiple herbicide sites of action vs. just multiple modes of action adds even more diversity to your weed management strategy.
All of these classifications are important to consider when developing a weed management plan.