Yucca (Yucca spp.) shrubs and trees, with their daggerlike evergreen leaves, seem as though they should be safe from pests. When you are poked just touching a yucca, it's hard to imagine anything wanting to eat one. Well, surprise! Some tough little pests like to munch on this perennial plant that thrives best in U.S. Department of Agriculture plant hardiness zones 4 through 11.
Mealy bugs look like little white masses of cotton and are found on the axils, where the leaves connect to the stem of the plant. They may also be found on the roots and lower surfaces of the leaves. Mealy bugs have a waxy coating that makes insecticides useless, but you probably don't want those chemicals around your kids anyhow. Using insecticidal soap, horticultural oil or a good blast of water takes care of the majority of them. Leave the rest to natural predators and beneficial insects such as green lacewings and parasitic wasps.
Scales are weird little insects; they don't look like insects. They appear as hard, round, brown spots on leaves and stems and may look much like part of the plant because they glue themselves to their hosts. You can control scale insects in the same ways that you can control mealy bugs.
Thrips are tiny, skinny insects that feed on yucca leaves, causing them to curl. In a healthy plant, thrips won't do too much damage. If you feel the need to control them, you can use the same recommendations as for controlling mealy bugs.
The Yucca Weevil (Scyphophorus acupunctatus) mainly attacks the cane of the yucca plant. If the botanical name acupunctatus makes you think of acupuncture, it should because -- like needles -- weevil larvae tunnel into the base of the flower stalks, killing the plant. The only treatment is prevention. Cut off damaged foliage and keep your yucca healthy so you can avoid weevils.
Yuccas are bothered by a particular mite called Tetranychus urticae, or two-spotted mites. Even if you have trouble seeing these tiny, moving dots on your plant, you may notice what appears to be a web under the leaves. These are best controlled by raising the humidity for the plant. Try spraying it with water regularly to wash away mites and webbing.
Burrowing animals such as ground squirrels, mice, rabbits and pack rats eat yucca plants if there is no other food around. You may be able to control them by using fencing, live traps or poison bait, but keep poisons out of reach of your little ones. In most cases, the leaves are only moderately damaged, which allows the plant to recover on its own, so you may not need to resort to poisons if you are patient.