Herbicides are poisons intended to kill weeds; but any type of poison should be handled with care and carries some inherent risks with it. Herbicides can do serious damage to plants, soil, water supplies, pets and people. Knowing the dangers and handling herbicides properly helps reduces the risks, but you should never assume that an herbicide is harmless in a lesser amount. Always take herbicides seriously and use them cautiously.
Herbicides applied at too strong a concentration can cause foliage burn on surrounding desirable plants; for newly planted specimens, foliage burn can be fatal. Take care by using herbicide only near healthy, established plants and by following package instructions for the correct concentration.
Whether in liquid or granular form, herbicides pose the risk that they will be carried into the water supply by rainfall. A significant amount of herbicide in a water supply can promote algae growth and harm aquatic life. Try to use herbicide when there is no danger of immediate rainfall, and never use herbicide on the banks of a stream or other waterway.
Because herbicides are poisons, they pose a threat to pets or people who ingest them accidentally. This is a significant risk for pets and children. Always keep pets and children inside when you are applying an herbicide, and read the package for the time period needed to allow the herbicide to soak in and/or wear off in potency. Supervise pets and children once you allow them back in the area where you have used the herbicide.
Long-Term Health Risks
Long-term health risks are not the same for every type of herbicide; for the home gardener using a bit of weed killer here and there, the risk is minimal. For a commercial farmer, spraying crops several times a season with a commercial-strength herbicide, long-term health risks are a valid concern, notes the Fred Hutchinson Cancer Research Center. Pesticides have been studied for links with health problems such as fibrosis and several types of cancer; though not all results are conclusive, it's using common sense to use caution with something that we know is toxic, whatever the real long-term effects may be.