Yellow fly bait crystals and strychnine are poisons that kill groundhogs when the animals ingest them. Methyl bromide is a fumigant that kills groundhogs when they inhale it.
Using poison to kill groundhogs is inhumane, as the animals can suffer internal bleeding, loss of muscle control, convulsions and painful sores for days before they succumb. Humans or other animals may be unintentional victims of poisons targeting groundhogs.
Using repellents, such as mothballs, Epsom salts and coyote urine, to deter groundhogs is a more humane method of eliminating a groundhog problem. Using humane traps to catch and relocate the groundhogs is another option. Installing fencing to keep groundhogs out of specific areas may also be effective.