Carpenterworms

• Exit holes are round and large, about 1/2 inches
• Galleries starting in sapwood eventually entering heartwood
• Large amount of sawdust often present at base of ash
• Heavily infested ash can become gnarled and misshapen
• Stout bodied moths, black and light gray mottled forewings as large as 2 1/2 to 3 inches
• Yellowish white caterpillars with brown heads; 2 to 3 inches long

Carpenterworm, Prionoxystus robiniae, is a common wood-boring insect that can cause significant damage to several species of ornamental and fruit trees. Trees that carpenterworms are most likely to infest include apricot, ash, birch, cottonwood, American elms, black locust, maple, oak, fruiting pear, ornamental pears, and willow. Locations near riparian areas are more susceptible to infestation.

The larval stage of the carpenterworm is a large, wood-boring caterpillar that feeds within a tree’s inner bark on the sapwood. The earliest signs of an infestation are dark sap spots on the tree trunk. As the larvae feed within the sapwood, they expel frass (excrement) and sawdust out of the gallery entrance hole. This material is readily observable on infested tree trunks.

As the larvae grow, they expand the galleries. By the time the larvae are mature, the galleries are about 1/2 inch in diameter and 6 to 10 inches long; most of the gallery is vertical, except for the entrance area. Gallery entrances often are found in crotch areas of trees or in cracks and crevices in the bark. Adult females frequently lay eggs in areas of the tree that already are infested, and multiple galleries might arise in the same area, leading to extensive scarring on the corky bark tissue.

When mature, larvae can measure up to 1/2 inch in diameter and 2 to 3 inches long. They usually are greenish white with a dark brown head. They also have prominent hairs on their body, distinctive abdominal prolegs, and sharp, hooked legs on their thorax.

The adult carpenterworm is a large, robust moth with a wing expanse of about 3 inches. The forewings are mottled black and gray, making the moths difficult to see when they are resting on a tree trunk. The male moth is somewhat smaller than the female, and its hind wings are orange and brown while those of the female are off-white.

The extensive feeding of carpenter­worms in large branches can cause branches to weaken and break in high winds. The potential for dropping limbs is a major hazard in urban settings. Branch girdling by carpenter­worms, a process that disrupts a tree’s flow of nutrients and water, also can cause dieback of branches.

When monitoring for carpenterworm, look for dark sap spots on tree trunks, large quantities of frass and sawdust expelled from galleries, or scarred bark. In older infestations, you might see pupal cases protruding about two-thirds out of the tree bark. Discolored or oozing bark and limb dieback can have other causes, including inappropriate cultural practices, pathogens, and other types of wood-boring insects, including bark beetles (family Scolytidae), clearwing moths (Sesiidae), flatheaded borers (Bupre­stidae), and longhorned borers (Cerambycidae). Because each of these pests requires different management practices, you’ll avoid ineffective control efforts by accurately identifying the cause of unhealthy trees before taking action.

Information source: University of California Agriculture and Natural Resources

Clearwing borers (Ash borer and banded ash clearwing)

• Exit holes first appear in June and July
• Exit holes are round and 1/4 inch wide; frass (sawdust and excrement) can be conspicuous underneath
• Galleries occur deep in sapwood
• Pupae stick out of exit hole, empty pupal cases are commonly observed after moths have emerged
• Adults are wasp-like, lacking scales on most of their wings
• Larvae are caterpillars; have a brown head and cream-colored body; up to 1 1/3 inch long

Early signs of clearwing borer infestation are wilting of terminal shoots, and branch and crown dieback. Infestation sites often are marked by cankers, calluses, or cracked bark. Large limbs may die or become so weakened that they are easily broken in the wind. Established trees may persist in poor condition and be re-infested year after year.

Clearwing borers expel coarse, brown frass (sawdust-like fecal material) from cracks in the bark. In some hosts, especially Prunus species, the frass may be mixed with oozing sap or gum. When the adult moth emerges, it leaves an empty, tan shell (pupal skin) that protrudes from the bark. Feeding holes left by woodpeckers or other birds may indicate that a tree is infested.

Adult clearwing borers are delicate, day-flying moths that resemble small wasps. The moths feed only on nectar or not at all so they do not cause damage. The larvae are whitish, hairless caterpillars with brown heads. The most damaging clearwing borers are associated with dogwood, lilac, ash, oak, rhododendron, and ornamental Prunus species, including flowering peach, plums, and cherries.

Information source: University of Kentucky, College of Agriculture, Food and Environment, Department of Entomology

Emerald ash borers

• Chewing damage caused by adults occurs late May to early August
• Chews along the edges of leaves; defoliation is typically minor
• Slender bodied, 1/3 – 1/2 inch long; iridescent green with coppery colored head

Flatheaded borers or Primarily Chrysobothris sexsignata

• Exit holes first appear in May and June
• Found nearly always in black ash
• Exit holes are oval shaped and 3/16 inch wide
• Galleries start in phloem and eventually enter into sapwood; generally not very serpentine
• Adults are 1/2 inch long, bullet-shaped, and bronzed colored
• Larvae are whitish, flattened, up to 1 inch long; area behind enlarged and flattened; head generally inconspicuous; legless

Information source: University of Minnesota

Redheaded Ash Borer

• Exit holes first appear in June
• Exit holes are round and 3/8 inch wide
• Galleries start in phloem and eventually enter into sapwood; generally not very serpentine
• Adults are 1/2 to 5/8 inch long; reddish brown with four yellow bands across their wing covers
• Larvae are up to 4/5 inch long, whitish, cylindrical; area behind head enlarged and round, head generally inconspicuous; legless

The redheaded ash borer, Neoclytus acuminatus, is a multicolored beetle in the family Cerambycidae. Adults have a reddish head and thorax, and have four bands of fine yellow hairs that cross the dark brown wing covers. Another striking feature of this insect is its legs: the middle and hind legs are long, with the second section (femur) swollen, appearing almost muscular. Overall, the redheaded ash borer is small, only 4-18 mm long.

Typical of native borers, the targets of the redheaded ash borer are stressed and dying trees. These trees can be mature or newly planted, or they can be recently cut and still green (unseasoned). The host list for this borer includes many hardwood tree species, but the favored hosts are ash, oak, hickory, persimmon, and hackberry. This insect will also feed in fruit trees, and the author has recovered redheaded ash borers from grapevines.

Adults emerge from infested host wood, chewing 2-5 mm diameter round holes. If the insect host has been made into firewood, the adults can emerge from wood stored in the home prior to burning. Redheaded ash borer adults are seen as a nuisance since they do not lay eggs on household wood or harm occupants.

Information source: Iowa State University

Woodpeckers

• Holes are roundish and range in size from 1/4 to 1/2 inch
• Larger holes, 1 1/2 or more inches may be nesting holes and suggest softer heartwood inside the tree
• Bark often removed around holes
• Woodpecker probing may indicate the presence of wood boring insects under the bark
• Repetitive tapping or drumming heard
• Birds of varying black and white patterns, often with some red, seen tapping on trees

Ash trees with the outer bark removed may be infested with either emerald ash borer or a native ash bark beetle. When woodpeckers remove outer bark of an ash tree, it makes the tree look very pale. Emerald ash borer populations build up to very high numbers as they move into new areas, which provides a great source of food for woodpeckers. A study published in 2012 showed that woodpecker numbers can increase due to the presence of EAB. Ash bark with pale areas where woodpeckers have removed outer layers of bark, as well as some small rough holes where the woodpeckers punched through the bark and plucked out a nice plump EAB larva.

Information source: Wisconsin DNR Website