The use of herbicides in certain situations may be needed, in conjunction with preventative measures that focus on reducing nutrient load in the water column. However, herbicidal applications can often cause a vicious cycle of chemical dependency.
Excess unwanted aquatic plants are typically the result of water containing high nutrients. The vegetation is not the problem, but rather a symptom of the underlying issue of more nutrients being produced than the beneficial bacteria present can consume.
When an herbicide is applied and the vegetation begins to die off, the decay process releases more nutrients into the already nutrient-loaded pond. More nutrients is the last thing you want when trying to reduce vegetation like duckweed. The nutrient spike triggers a regrowth in weeds, spurring the application of more herbicide, and the cycle repeats over and over again.
If you can reliably remove vegetation before it begins to decay, some herbicidal use can be helpful in removing invasive plants.
You may also want to use herbicidal treatments in conjunction with a biocatalyst that damages the plant’s defenses against attack. A biocatalyst like Naturalake’s Aquasticker works in multiple ways to increase an herbicide’s effectiveness.