Plant Health Problems
Ornamental species of yucca are relatively disease-free under most
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