Weed resistance is a concern for farmers throughout the world as weeds continuously evolve and become less susceptible to various herbicides.
The rise of weed resistance can impact growers on two fronts – reduced yield and increased input costs for weed control. Managing resistance involves various approaches, including mixing up herbicide modes of action and application timing.
Herbicide resistance is the evolution of a weed population to survive an application of a herbicide that previously provided effective control. When herbicides with the same mode of action are used continuously over time, resistance can occur. The few weeds possessing genetic mutations that allow them to survive the application of the herbicide and, through reproduction, will be the dominant population after a few generations.
To this effect, farmers need to apply herbicides and/or tank-mixes with multiple effective modes of action to slow the development of resistance.
Application of a multi-pronged approach
General strategies to reduce the weed seed bank, control emerging weeds before they compete with the crop, and target them when they are most vulnerable usually include:
Soil-active residual herbicides: Preventing early emergence
A pre-plant soil-active residual herbicide application is made for the purpose of controlling weed seeds and weed seedlings before they become a problem. Soil-applied residual herbicides control weeds as they germinate or emerge through the soil surface. Soil active herbicides may remain active for several weeks or even months and, as such, can provide long-lasting protection during the most critical early stages of crop growth.
Some advantages of a soil-active residual herbicide application are:
- Reduction of weed seed banks: Soil active residual herbicides target weeds as they germinate and before they have a chance to set seed, thus helping reduce the overall weed seed bank in the field.
- Extended protection: In a season when conditions delay the application of pre-seed or in-crop herbicides, residual herbicides can offer protection and help keep populations in a susceptible stage until the next herbicide application.
- Increased herbicide diversity: Soil active herbicides typically allow growers to incorporate different modes of action at a new or different application time. This is another way to throw weed populations off their game that may have adapted their growth cycle.
Fierce EZ herbicide is an excellent soil active herbicide which offers residual control of both broadleaf and grass weeds. It features two modes of action, Group 14 and 15, and uses active ingredients that aren’t typically used for in-crop applications.
Pre-seed burn-down herbicide: Clear the field before planting
A pre-seed burndown application is a great way to clean up fields before seeding.
Key benefits of pre-seed burn-down herbicide application:
- Improved crop establishment: Weeds that emerge before planting can challenge the crop during critical growth stages by competing for nutrients, light and water.
- Control of tough weeds: Many tough broadleaf weeds, such as kochia and cleavers, are controlled more effectively with a pre-seed burn-down treatment, when they are smaller in size.
- Resistance risk reduction: Pre-seed timing is another chance to include a mode of action not typically used during in-crop application timing. Tank-mixing multiple modes of action and rotating different modes of action throughout the season can help slow the development of resistance.
In-crop herbicide: Application for weeds during the growing season
In-crop herbicides are important because they are the last chance to control weeds before harvest.
Key advantages of in-crop herbicide applications:
- Selective control: In-crop herbicides are formulated to control weeds without damaging the crops to help maintain yield and quality.
- Managing escapes: Even with pre-seed and residual herbicide treatments, some weeds may still germinate later in the season. In-crop herbicides provide a crucial tool in managing weed escapes or late flushes.
- Maximizing efficacy at in-crop timing: In-crop herbicides should be part of a season-long weed management plan. Through thoughtful planning another herbicide group can be added to the rotation at in-crop timing. In-crop herbicides will work best on actively growing weeds. Lots of in-crop herbicides rely on making contact with the weed, so use enough water (often a minimum 10 gallons/acre) to get good coverage on targeted populations.
Herbicide resistance has been presented as a complex issue and an increasing problem. While we can’t stop weeds from developing resistance we can slow down the development by rotating herbicide groups through soil active, pre-seed burndown and in-crop herbicide applications. When possible growers should tank-mix more than one effective mode of action on the targeted species and consider adding cultural and mechanical practices to their operation..
