Cacti are classified as succulents because of water-storing stems that aid their survival in dry, hot regions. While some people grow cactus gardens intentionally, not everyone enjoys these prickly characters. In many areas, wild cactus can overtake an area and become hard to control. Part of the problem is that the root system survives even when the above-ground portion of the plant is destroyed. Permanent removal of a cactus requires an application of chemicals that seep down and kill the root system.
Fill a backpack sprayer or a hand-held garden sprayer with an herbicide with the main active ingredient picloram. Mix the herbicide with cold water to create a 1 percent solution. For a 3-gallon sprayer, add 3 gallons water and 4 ounces of herbicide.
Add 1 ounce of a non-ionic surfactant to the tank. This is available in the weed control aisle of many hardware stores and garden centers. If desired, liquid dish soap can be substituted for the surfactant. Surfactants help the herbicide stick to the cactus better.
Add 1 to 2 ounces of a spray marking dye to the sprayer. This colors the spray so you can easily determine where you've sprayed and when the cactus has been completely saturated.
Close the sprayer and rock it back and forth gently to mix the solution. Don't shake it; bubbles will form and you'll have to wait to spray.
Spray all surfaces of the above-ground portion of the cactus plant until they are completely covered in dye, but not so the spray drips or runs down the plant.
Wait until the cactus is completely dead and brown. Your herbicide's label should note how long this may take, but some cacti take one to two years to die. When the cactus is brown, cut off the top portion with a knife. Wearing work gloves, dispose of the plant in the trash.