Lilac/Ash Borer: a Common Wood Borer of Colorado’S Street Trees Fact Sheet No

Lilac/Ash Borer: A Common Wood Borer of Colorado’s Street Trees Fact Sheet No. 5.614 Insect Series|Trees and Shrubs by W.S. Cranshaw* Lilac/ash borer (Podosesia syringae1) is Quick Facts common wood borer associated with ash throughout Colorado and a species that is • Lilac/ash borer is an native to North America. Damage is caused insect native to North by the larvae which tunnel into the trunks America that is common and lower branches of ash trees. These in ash trees, particularly if feeding injuries produce irregular gouging trees are stressed due to wounds under the bark and tunneling drought, injury or that were frequently extends deeply into the heartwood recently transplanted. (Figure 1). Almost all larval feeding activity occurs in the lower trunk, particularly around • Damage is done by the larva; the soil line (Figure 2). Lower scaffold limbs a type of caterpillar that may also be attacked and infestations may tunnels into the trunk and extend about 10 feet up the trunk. Feeding lower branches of ash trees. damage can often be found in the mid and upper crown of trees above areas that were • If necessary, lilac/ash borer treated with contact insecticides. can be easily controlled by External evidence of lilac/ash borer spraying the trunk and lower activity in trees can include irregularly Figure 1. Lilac/ash borer larvae tunneling branches in spring during round exit holes of about 1/4-inch diameter exposed from under the bark. Photograph by the time when adult females David Leatherman. on trunks (Figure 3). As larvae near full- lay eggs on the trunk and the development some sawdust may be expelled newly hatched caterpillars from these holes and, when adults emerge, these plants is much less frequently observed begin to tunnel into the wood. the pupal skin often remains extruded in Colorado. On lilac and privet, damage is from the hole (Figure 4). Ash trees heavily confined to the base of the plant. On smaller • Lilac/ash borer should not damaged by lilac/ash borer often show diameter branches, such as is common with be mistaken for the emerald some disfiguring of the trunk, with areas lilac and privet, larval injuries may girdle and ash borer, an introduced of irregular, gnarled growth, and often kill stems. insect of Asian origin that development of excessive branching. The larvae are creamy white grubs with was recently found in a part Extensive tunneling of the lower trunk may a small dark head (Figure 5). Prolegs on the of NE Colorado and is far seriously weaken plants and cause them to underside of the abdomen are highly reduced more seriously damaging to break. Trees may be killed by this insect, but elliptical rings of small hook-like crochets ash trees. although that is rare. are readily visible at the tip of the prolegs. Serious problems almost always The presence of abdominal prolegs allows involve ash grown in suboptimal locations separation from lilac ash borer larvae from (e.g., parking lots, street trees) or recently those of the various other wood borers found transplanted trees. Damage is usually in ash, all of which are larvae of beetles. insignificant to well established trees that Adult lilac/ash borers are mimics of receive adequate water and care. In Colorado, Polistes paper wasps, quite similar in both more problems have been associated with size and coloration (Figure 6). The wings are white ash (e.g. ‘Autumn Purple’) than green dull black with chestnut brown tones and ash. Lilac (Syringa) and privet (Ligustrum) wingspan typically ranges from 28-35 mm © Colorado State University are other hosts for this insect but damage to (ca 1-inch). The body is generally dark brown Extension. 5/14. with reddish markings and narrow yellow www.ext.colostate.edu *Colorado State University Extension entomologist bands occur on the abdomen. Long hind legs and professor, bioagricultural sciences and pest also reinforce the superficial similarity with management. 5/2014 paper wasps. Lilac/Ash Borer Life History Note on Emerald and Habits Ash Borer The ash borer spends the winter as a The most serious pest of ash in partially grown larva within tunnels under North America is the emerald ash the bark. It resumes feeding and larval borer, Agrilus planipennis. The development in early spring, pupating emerald ash borer is an Asian insect just under a thin cover of the bark. Adults that is not native to North America, emerge during the morning (8-11:30) but was accidentally introduced into on warm (above 60°F) days in spring. the US and first found in the Detroit Depending on location in the state and area in 2002. Since then emerald seasonal temperatures first emergence of ash borer has devastated all North the adults begins within a range of early American species of ash—including April to early May and typically lasts for the green ash and white ash grown about 4-6 weeks. During emergence the commonly in Colorado—killing pupal skin is often partially pulled through tens of millions of trees. As of 2013 the emergence hole and visibly extrudes it had extended into 22 states from the trunks of infested trees. Lilac/ash and was first found in Colorado borer is one of only a few kinds of moths that fly during the daytime. Figure 2. Tunneling produced in the base of a in September 2013. Presently the recently transplanted “Autumn Purple” white ash infestation of this insect within the Shortly after mating the females begin by the lilac/ash borer. state is thought to be confined to to lay eggs. These are deposited singly or Boulder but it is expected to spread in small groups in bark crevices on the over the next decade to include lower trunk. Adults are short-lived and much of northeast Colorado (South typically deposit all eggs within a week after Platte drainage). emergence. Eggs hatch about 9-13 days after they have been laid. Emerald ash borer is a very The larvae hatching from the eggs enter different insect than is lilac/ash the trunk and initially feed in cambium and borer and is far more damaging phloem. During this feeding phase they to ash trees. The pattern of injury will excavate an irregular, shallow gallery that it produces is different from that may be 1-3 cm wide and 2-5 cm long. lilac/ash borer in that the larvae They then move into the trunk and tunnel Figure 3. Irregularly round exit holes produced make meandering tunnels that are upwards for an extended period, producing when adult lilac/ash borer emerges from the restricted to areas immediately a tunnel that may extend 7-32 cm. When trunk in spring. under the bark and attacks often full-grown in late winter, they move back concentrate originally in the upper to the cambium and produce a pupal crown of the tree (Figure 7). chamber just under the bark, with a paper These injuries are quite dissimilar thin covering that the adult can later push to the irregular tunnels confined through (Figure 8). One generation is to the lower trunk produced by produced annually. lilac/ash borer, which may cause Control of Lilac/Ash Borer. High-risk considerable internal riddling. ash trees may benefit from control of lilac/ Adults of the emerald ash borer, ash borer. These could include recently a type of metallic wood borer transplanted trees, trees in poor sites, trees (Coleoptera: Buprestidae), emerge receiving limited water, or trees that show from D-shaped exit holes in the significant effects of previous damage. bark, in contrast to irregular round Activities that can relieve tree stresses, such emergence holes of the lilac/ as provision of supplementary watering, ash borer. should be considered part of any program for lilac/ash borer control. Information on emerald ash Treatments involve use of insecticides borer in Colorado can is available applied to the bark in a preventive through county offices of CSU manner to kill larvae before they enter Extension, Colorado State Forest the trunk. Certain pyrethroid insecticides Service offices and the Colorado used to control wood boring insects Figure 4. Trunk of an ash tree showing Department of Agriculture web site: irregular areas of bark produced by lilac/ash (e.g., permethrin, bifenthrin) have long borer wounding. Two pupal skins of the insect www.eabcolorado.com. been standards for this application, and extruding from the trunk are visible on the left. some permethrin formulations useful for control of this insect are commonly available through many nurseries and hardware store outlets. More recently an alternative insecticide, chlorantraniprole (Acelypryn), has become available to commercial applicators. Soil-applied systemic insecticide applications of imidacloprid are not recommended for control of this species of borer, largely because imidacloprid has poor activity against larvae of moths. Trunk sprays should be applied shortly before or coincide with the anticipated time of egg hatch. This occurs about 10-14 days after adults begin to emerge from trees, Figure 8. Pupal skin of the lilac ash borer Figure 5. Larva of the lilac/ash borer. typically sometime between in mid-April extruding from the trunk. Photograph courtesy of David Cappaert/ and mid-May. Michigan State University and www.bugwood. Traps containing lures with the org. ‘clearwing borer’ sex pheromone can be very useful for detecting the onset and length of lilac/borer flight activity in the spring (Figures 9, 10). These traps also capture several other types of clearwing borer moths, notably the peach tree borer (Fact Sheet 5.566) and cottonwood crown borer/American hornet moth (Sesia tibialis). These moths fly a bit later in the season than does lilac/ash borer but may co-occur in traps during June and early July.

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