Bugs on yucca plants

Yucca Plant Bug

I’ve long admired yucca (Yucca spp., family Asparagaceae) but realize many do not share my enthusiasm for these cousins to agave. Indeed, searching the web using “yucca” as the keyword yields almost as many websites offering advice on how to kill it as how to grow it.

My yuccaffection stems from growing up in Appalachia where the two most common flowering plants in farmhouse landscapes seemed to be peonies and yuccas. In my neck of the woods, the yuccas were called “ghost lilies” owing to the way the vivid white flowers borne on upright stalks resembled luminescent apparitions at night. They were a great accompaniment to late-night ghost stories on the front porch.

However, yucca plant bugs (Halticotoma valida, family Miridae) can cause serious harm to their namesake host by using their piercing-sucking mouthparts to extract the essence of yucca. Indeed, I watched a historic planting of Yucca filamentosa ‘Adam’s Needle’ that was established in the late 1800s in Spring Grove Cemetery and Arboretum become seriously depleted due to plant bug damage. Tom Smith, a retired vice-president of Spring Grove and another yucca-lover, was the first person to alert me to yucca plant bug.

Both adult and immature (nymphs) yucca plant bugs have a somewhat oval-shaped body. Adults of this small (3/16″ long) native of the southwestern U.S. have black wings and orangish‑red legs, head, thorax, and abdomen. The nymphs share this striking color scheme, but they appear more reddish in color since their black wing pads fail to cover their entire abdomen.

Yucca plant bugs may feed on several species of yucca beyond Y. filamentosa. Feeding damage by the adults and nymphs produces small, yellowish-white spots (stippling) which may coalesce causing the foliage to turn yellow then brown. The bugs further reduce the aesthetic value of yucca blades by depositing spent yucca extract in the form of black, tarry waste spots.

Feeding on yucca flower stems can reduce flower production. Intense annual feeding activity on yucca blades reduces plant vigor and can eventually cause plants to die.

The bug spends the winter as eggs inserted into the yucca leaves. Eggs hatch in early spring and there are at least three overlapping generations, so populations can build rapidly. Adults are present well into the fall.

Yucca plant bug is a common problem on yucca, particularly in the southern U.S.; however, I could find no published insecticide efficacy trials. Based on personal observations, using direct contact insecticides such as insecticidal soap is problematic. These bugs are very visual; they see you (or a spray nozzle!) coming and quickly drop from the yucca blades. Residual insecticides such as pyrethroids appear to provide limited efficacy because they work best if consumed by insects with chewing mouthparts.

Systemic insecticides have been effective. In fact, Spring Grove was the first place I ever saw imidacloprid (e.g. Merit, Xytect) effectively used to suppress an insect pest; yucca plant bugs. Later applications involved dinotefuran (e.g. Safari, Transect) which was equally effective. Impact on pollinators is minimal because yucca flowers are not visited by general pollinators. They’ve evolved with their own specialize mutualistic pollination system involving yucca moths (family Prodoxidae). Of course, any pollinator concerns can be addressed by delaying applications until after flowers have declined.

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Wednesday – August 06, 2008

From: Port Monmouth, NJ
Region: Mid-Atlantic
Topic: Pests, Cacti and Succulents
Title: Bugs on yucca plant in New Jersey
Answered by: Barbara Medford

QUESTION:

I noticed small bugs ALL OVER 4 established yucca plants all near each other. They may look like Halticotoma valida but I’m not positive. There is no brown on the leaves except for the large amounts of bugs scurrying about but the leaves are no longer fully green or straight up. The leaves seem very muted in color and they seem to be wilting more and more. HELP!! How do I get rid of them before they kill my plants?

ANSWER:

We’re still trying to get our minds around there being yucca in New Jersey. There are 28 plants that either are yuccas or have “yucca” in their names in our Native Plant Database. As we went through trying to find a likely candidate, we found that most of them listed their native habitat as Arizona, New Mexico and Texas. Finally, we found one, Yucca filamentosa (Adam’s needle) that is known to grow in New Jersey. There is also Hesperaloe parviflora (redflower false yucca) but it didn’t appear to be growing anywhere outside the desert Southwest, either. Do you know which yucca you have?

The Floral Genome Project Yucca filamentosa has some general information on this plant. Nearly every website we visited on yucca assured us that there were no significant pests or diseases of the yucca if its cultural requirements were met. However, we did at last find a site that admitted they might have infestations of Halticotoma valida. See if the images on the referenced site match the bugs you are talking about. We also found several references to mealybugs as being a nuisance to yuccas. This eHow site gives you complete instructions on How to Control Mealybugs. Here is a page of Images of mealybugs. And, finally, here is a Connecticut Agricultural Experiment Station website on the Plant Health Problems of Yucca . The Lady Bird Johnson Wildflower Center neither recommends for nor against pesticides, but these sites have suggestions for the specific bugs in question. Always read directions carefully and follow them to the letter when applying pesticides.

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Do you have yucca planted in your landscape? Have you checked it lately for pest problems? I know that it seems early to start checking for pests but I walked past the yucca at the office this week and it is covered with yucca plant bugs already.

Yucca plant bugs are in the order Hemiptera and are related to other sucking pests such as stink bugs and leaf-footed bugs, but are much smaller. Adult yucca plant bugs have a bright reddish-orange head and thorax with dark bluish-black wings. Immature yucca plant bugs (nymphs) look similar to adults but do not have fully developed wings. Since immatures do not have their wings fully developed, they’re more red than black in color.

Both immatures and adults feed on plants by piercing plant tissue with their mouthparts causing yellowing spots on the foliage.

These little critters can sometimes be a challenge to manage since when you go to treat for them, they all dive into the center of the yucca into the nooks and crannies to hide. You can try products with active ingredients such as insecticidal soap, horticultural oil, azadirachtin (neem), pyrethrins or bifenthrin, cyfluthrin, or carbaryl. You will need to get good coverage to make sure that you get the pesticide to where the insects are hiding (and be careful not to get stabbed by the yucca!).

Connecticut State The Connecticut Agricultural Experiment Station

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.

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