• Feb 19, 2018

Are Your Herbicide Sites of Action Effective?

Sprayer Nozzle
As new herbicide technology hits the market, there has been even more discussion about the battle against resistant weeds. The International Survey of Resistant Weeds reports there are 160 weed species in the U.S. that are resistant to at least one herbicide class. But how does resistance happen and what can you do to help combat the problem?
Rise of Resistant Weeds
Resistance starts with a small number of weeds that carry mutations making them more tolerant to specific herbicides. This happens spontaneously, in the same way that mutations happen in our own DNA. The problem arises when we inadvertently give these weeds the upper hand by selecting for them when we apply herbicides that they are tolerant to.
Herbicide-tolerant weeds are selected for when there is a spray program that lacks diversity, meaning herbicides with the same sites of action are continuously applied. Every time a weed escapes control, it has the potential to make seed. Those seeds end up in the soil and the next generation of weeds have more tolerance to the herbicide they are developing resistant to. If the same herbicide class is used without including additional effective sites of action for control, the cycle continues until resistant weed populations have taken over.
Break the Cycle
The good news is that you can stay one step ahead of resistance by diversifying your spray program. The goal is to limit weed escapes by using multiple site of action herbicides in your tank mixes. It’s also important to layer herbicides throughout the season and incorporate residual products to get extended windows of coverage. These strategies all help attack the defenses of weeds that have become adapted to the environments they are thriving in.
Some weeds have documented resistance of up to four different sites of action, so don’t assume adding multiple site-of-action herbicides to your tank will be enough. Make sure the products you are using are actually effective against the weeds you are trying to control.
The website Take Action on Weeds has a tool that identifies sites of action for most common herbicides to help you diversify your spray program. Alternating herbicide sites of action can help extend product life and reduce the likelihood that weeds will develop resistance. Talk to your local retailer to learn more about effective weed management strategies.