Herbicide(s) , also commonly known as weedkillers, are pesticides used to kill unwanted plants.Selective herbicides kill specific targets, while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic mimics of natural plant hormones. Non-selective herbicides: These herbicides are not specific in acting against certain plant species and kill all plant material with which they come into contact. 2  They are used to clear industrial sites, waste ground, railways and railway embankments.