Plant Health Problems

Ornamental species of yucca are relatively disease-free under most conditions.

Insect Problems:

Yucca plant bug, Halticotoma valida.
This is a small blue-black true bug with a reddish head. Adults and nymphs damage foliage by sucking plant sap. Symptoms of feeding are yellow, stippled new foliage. Among the compounds registered for control of this pest in Connecticut are insecticidal soap, ultrafine horticultural oil or malathion. When needed, apply foliar sprays to contact the insects. Alternatively, imidacloprid can be applied as a systemic to be taken up by the roots. Consult the label for dosage rates and safety precautions.

Mealybug, Planococcus citri.
Only certain yuccas are susceptible to mealybugs. When needed, they can be controlled with the use of insecticidal soap, ultrafine horticultural oil or malathion, which are among the compounds registered for control of this pest in Connecticut. Spray needs to contact insects in order to be effective. Alternatively, imidacloprid can be applied as a systemic to be taken up by the roots. Consult the labels for dosage rates and safety precautions.

Oystershell Scale, Lepidosaphes ulmi.
This and other scales occasionally attack yucca. Control is rarely needed.

Stalk borer, Papaipema nebris.
This borer infests an occasional stalk of many kinds of herbaceous plants, including yucca. The larva tunnels up and down inside the flower stalk and the top portion usually wilts and later dies. There is one generation each year. The moths emerge in September and October and lay eggs on the stalks of their food plants, in which stage the insect passes the winter. The eggs hatch in May or early June. The young larva begins to feed on the leaves of the nearest food plant, and later tunnels in the stem. The mature larva is nearly 1 ½" long, grayish brown with one white stripe on top and two white stripes on each side. On the front half of the body the lateral stripes are interrupted, and the lower brown stripe extends forward onto the side of the head.

Burning all the old stalks, if allowed, and destroying weeds at the edges of the garden helps control this insect. When needed, methoxychlor, which is among the compounds registered for use against this pest in Connecticut, applied as a dust, in June, should control this pest. Consult the label for dosage rates and safety precautions.