Yucca is a flowering perennial plant that is often planted in home landscapes as a conversation piece. However, if left untended, yucca can grow invasively and develop dense stands that may soon dominate the landscape. And because of their thick growth and deep tubers, it can be difficult to kill yucca plants with herbicide alone. To permanently destroy a stand of these tough plants a combination of control methods is often necessary.
Dig up the yucca plants. Use an axe or a pair of lopping shears to cut each yucca plant down (or close to) to soil level. Then use a shovel to dig up all of the underground tubers underneath the plant. Even small pieces of yucca root may be able to regenerate. Discard or compost the foliage and tubers when all of them are removed.
Spray the center of each yucca plant's leaf whorl with a broad spectrum dicamba herbicide. Use gloved hands to move the spiny leaves aside and target the center of the plant. Spray until just before the point of runoff according to the manufacturer's instructions. Respray all plants as needed at the intervals dictated by the product's manufacturer.
Search for sprouting yucca plants for the next few seasons after you have killed the main stands. Dig or spray these young plants as soon as you spot them to reduce the likelihood that the plant will have a chance to re-establish itself.