Battle of the Bugs by George Giltner, Louisiana Master Gardener
The carpenterworm moth larvae, Prionoxystus robiniae, feeds on local species of oak, locust, maple, willow, ash, walnut, American elms, fruiting pears, and ornamentals. Therefore if you observe a weeping ooze and brownish frass from these trees you should have concern. If the caterpillar has been active for an extended period of time, the tree will be deformed due to tunneling damage. The ¼ – 3 inch larvae are greenish white to pinkish with a dark brown head. Other identifying features are the prominent hairs on their body, hooked legs on their thorax, and distinctive abdominal prolegs. The adult moths have a mottled black and gray wing span of 3 inches. The male has orange and brown hind wings while the female’s hindwings are white.
Images 1 & 2: Adult moth on left & larva on right.
The adult moths mate from late April to early June, then lay 3-6 oblong olive green eggs in crevices or wounds of the tree. Within the two weeks the eggs hatch, then the larvae feed on the inner bark to the sapwood for 2-4 years. Pupation is in the heartwood. In 20 days, the adult moth emerges in daylight, leaving the pupal case on the outer bark.
How do you control these boring caterpillars? With early detection and a light infection site, your best bet is to use beneficial nematodes, Steinernema feltiae and S. carpocapsae. A squeeze bottle, syringe, or an oilcan makes a good application device for a water injection at the bark tunnel entrance. Any extra nematodes can be used to control fungus gnats, leaf miners, domestic flies, Japanese beetles, and sweet potato weevils. Websites for ordering the nematodes are: www.gardeningzone.com/products/nematodes, www.bugsforgrowers.com/products/steinernema-feltiae, www.groworganic.com/parasiticnematodes
Nematodes are live worms that do not do well with shipping in our hot summer climate or cold winters. The best time for ordering is in the fall and spring when temperatures are moderate (60 to 70 deg. F) nationwide. Schedule quick delivery. Pick up quickly from the mail box. Then apply soon after arrival in the evening. Seal the tunnel entrance of caterpillars with caulk.
Chemical insecticide applications of carbaryl or permethrin are not effective or are partially effective. The best way to control heavy infections is to cut and burn the tree. The females are not good fliers, thus the infection range tends to be more localized.
If you suspect you have carpenterworm moth in your trees, call the LSU AgCenter in DeRidder, LA at 337-463-7006.