Preventing Herbicide Resistance in Aquatics

As aquatic resource managers, we have a responsibility to be stewards of the environment and manage our waterways safely. Through quality management practices, we must ensure pesticides are applied responsibly and prevent unnecessary problems. To prevent herbicide resistance in plants, best practices include properly dosing and rotating the herbicides we use. 

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Herbicide resistance is a plant's ability to survive and reproduce after being exposed to an herbicide at a rate that would normally be lethal. Herbicide resistance develops in two ways. Individual weeds within a plant population can naturally evolve and develop defense mechanisms against threats, including herbicides, by changing their metabolic processes or developing thicker cuticles. Some weeds can even detoxify an herbicide on the interior of their cells, rendering it ineffective. This adaptability can allow weeds to survive and reproduce despite herbicide treatments. However, herbicide-resistant biotypes actually do occur naturally within weed populations. These random genetic mutations are initially rare and exist at a very low frequency. When the same herbicide is used year after year, these outliers will survive and reproduce until they are the only population members. After multiple life cycles, an entire population of plants can become resistant to a specific herbicide. When resistance occurs, the active ingredient previously used is rendered ineffective, which can force aquatics managers to use less desirable options to achieve the same results. This may include increasing herbicide rates, resulting in a larger volume of product needed for treatment, causing ecological and economic strain. As herbicide resistance increases, resource managers will have fewer and fewer options to control target weeds. 

Herbicides are classified in groups based on their mode of action, or how they affect target weeds. To prevent the spread of herbicide-resistant plants, it is important to rotate and use different groups of herbicides each year. Typically, herbicide-resistant plants become resistant to a specific mode of action. To prevent these plants from prospering, we can control them with an herbicide that uses a different mode of action than what was previously used. For example, rather than treating Cattails (Typha spp.) with Glyphosate 5.4 year after year, use Imox in subsequent years to introduce another mode of action and prevent herbicide-resistant breakthroughs. Below is a chart showing examples of the mode of action and herbicide group of each Alligare aquatic product to help you choose a solution, based on how it affects target species, when rotating herbicides to prevent resistance. 

Herbicide Brand Name 

Active Ingredient 

Herbicide Group 

Mode of Action 




Electron Diverter 

Flumigard SC 



PPO Inhibitor 




PDS Inhibitor  

2,4-D Amine 



Synthetic Auxin 

Triclopyr 3 



Synthetic Auxin 

Glyphosate 5.4 



EPSP Synthase Inhibitor 




ALS Inhibitor 

Imazapyr 4SL/ Ecomazapyr 2SL     



ALS Inhibitor 

Imox herbicide

It is important to note the failure of an herbicide to control a specific weed does not always indicate resistance. Underlying factors such as environmental conditions, growth stage of the target species, improper application, or incorrect herbicide selection can be attributed to lack of control. However, understanding how herbicide resistance develops is important when planning and implementing effective management strategies. If you do have an unsuccessful treatment, it is recommended you consult an Alligare representative to ensure an appropriate herbicide was used at the proper dosage rate for the targeted weed. If that is not the case, and the target weeds do have a history of treatments, resistance is likely. 

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