While herbicides play a useful role in eradicating unwanted plants, they also pose certain risks. When deciding to use herbicides, weigh the potential benefits against the risks. In some cases, such as removing a particularly stubborn invasive species that might spread to woodlands and destroy wildlife habitat, the use of an herbicide might be justified. In the case of weeds that are easily pulled by hand, the danger may not be worth it.
Herbicides can remain in the soil, or drain off to nearby soil, killing not only intended weeds or plants, but also those you are trying to grow. It can render certain areas incapable of sustaining the growth of any plant, unless the soil is removed and replaced.
Use of too much of a particular type of herbicide on a regular basis can cause stubborn weeds to become resistant to the herbicide, just as certain bacteria can become resistant to antibiotics if they are used too often. Sometimes applying more herbicide will kill the resistant plant, but causes other side effects such as additional soil contamination or increased resistance.
When herbicides run off into streams, rivers, lakes and other bodies of water they can create a devastating ripple effect. They may stunt the growth of plants that aquatic animals rely on to survive, or they may directly poison animals such as fish and frogs. A study by the University of California at Berkeley found that a certain herbicide feminized frogs and rendered some of them sterile.
Herbicides, even when carefully applied to a specific area can be toxic to animals, children and the person applying the product. Birds, mice, lizards and other animals may ingest part of the plant, causing themselves physical damage. Children who touch or eat the treated plants may also experience symptoms such as rashes, upset stomach and headaches. Prolonged or continued contact can result in more serious health problems such as cancer and decreased fertility.