I. Introduction: A relatively new problem (1980s) involves larvae of this insect developing in "burr knots" (adventitious root primordia) in above-ground portions of clonal rootstocks (photo 1). Dogwood borer (DB) is a sesiid, or clearwing moth, the larvae of which are tree borers. DB has been called the most common sesiid in North America, although not of much economic importance except to pecan in earlier years.

II. Hosts: DB has a wide host range (probably the greatest of any American sesiid), including apple, plum, bayberry, beech, birch, black cherry, blueberry, chestnut, dogwood, hazel nut, hickory, mountain ash, oak, pecan, pine and willow.

III. Description: DB is a slim moth with a steely-blue or black body with two thin yellow abdominal stripes (the stripe on the fourth abdominal segment is heavier than that on the second segment). There is a rounded anal tuft on the tip of the abdomen (triangular or pointed in many other species). The forewings are transparent with a dark outer margin. The wing length is 3/16 to 3/8 inch (5-10 mm) (females in the upper part of the range); the total wingspan ranges from 5/8 to 3/4 inch (16-19 mm). Hind tibia are yellow with a dark band between spurs. Larvae are white with a light brown head (photo 1), reaching a length of 5/8 inch (16 mm). The pupa is brown, about 3/8 inch (10 mm) long, and is usually found surrounded by a cocoon of silk and frass.

IV. Biology: DB is distributed from southeastern Canada and New England, west to Ohio and Minnesota, and south to Texas. This species probably has a single generation over most of our area, although with a prolonged period of activity. There is evidence for two generations in Kentucky and Tennessee, but even in areas with one generation, adults are present throughout the summer. The beginning of activity in Virginia is in early to mid-May, increasing in mid-June; in the Virginia study, there was a large second peak of flight activity in late July through early August. In Michigan, emergence starts in mid-June, peaking in early July, and ending in August. In some areas a second peak is present in early August. The second peak of DB is more likely to reflect infestation of apple and other alternate hosts, rather than dogwood. Hence the large late peak of flight activity noted in our region may be of special concern.

Eggs of DB are laid singly in wounds on the tree, and hatch in about nine days. There are seven larval instars, with development occurring in galleries beneath the tree bark. Larvae overwinter in various stages in these galleries and pupate in the spring just below the surface of the bark. The pupal stage lasts about 25 days. After the moth emerges, the empty pupal skin is left protruding from the bark surface. Adults are most active at dawn and twilight hours; most sesiids are active during the day. Adult longevity is six to eight days.

V. Injury: DB is a wound invader on its diverse hosts. It treats burr knots as wounds, with females laying eggs at such sites. Reddish-brown frass at burr knots is a sign of infestation (photo 2). While the burr knots themselves disrupt sap flow, girdling is enhanced once larvae are present. Furthermore, once established, feeding may extend beyond the burr knot into healthy tissue. Some scion/rootstock combinations may produce burr knots high on the trunk or at the base of limbs (e.g. `Gala' on M.26 or M.7a). This borer may exploit such sites. DB may also infest callus tissue at the rootstock/scion union, as well as gall tissue on hosts (e.g. black knot on plum). Chronic infestations will cause a decline in vigor and yield, and may rarely kill the tree. One New York study found that an average of 30 percent of trees were infested with DB (orchards ranging from 0 to 100 percent infestation). DB has been a serious problem in Michigan as well.

VI. Monitoring: Pheromone traps may be used for monitoring adult male emergence of DB, and should be installed during bloom. Research in Virginia has shown that traps baited with the lilac borer pheromone are more effective at catching DB than are traps baited with the DB pheromone. Research in New York has shown that trap height is critical for capture of DB. The optimal height is four feet (1.2 m) above the ground; one foot (0.3 m) in either direction may reduce captures by five-fold. Traps for DB are not very species specific, and may also capture lilac borer, Podosesia syringae (Harris); oak borer, Paranthrene simulans (Grote); maple callus borer, Synanthedon acerni; peachtree borer, S. Exitiosa (Say); rhododendron borer, S. rhododendri (Beutenmuller); and apple bark borer, S. pyri (Harris). Burr knots should be examined for the presence of protruding pupal skins (photo 3). No thresholds are currently available.

VII. Management: Tree guards, such as the plastic spiral-type (photo 1), can result in a problem with DB by creating a damp environment that is favorable for burr knots, and by preventing pesticide sprays from contacting the lower trunk. Tree guards with a more open mesh are recommended to facilitate air circulation and entry of sunlight to promote drying of burr knots, and to permit spray penetration. Mounding of the soil around burr knots that form between the ground and graft union will also prevent DB from infesting these sites. Lorsban is recommended for control, with handgun applications directed to burr knot-affected areas being most effective. Sprays later in the summer, during the fifth and sixth cover period, are more important than sprays at first and second cover. Researchers in New York obtained god control with a single spray timed for either first or peak egg hatch. In that study, first hatch occurred nine days after first pheromone trap catch. Peak egg hatch occurred on August 2, 20 days after peak catch. Research on degree-day accumulation has been variable, and average dates are still better predictors of development than thermal units.

Credits: Text prepared by H. W. Hogmire, modified from the original text in the Mid-Atlantic Orchard Monitoring Guide (original text by D. G. Pfeiffer, L. A. Hull, D. J. Biddinger and J. C. Killian).  Photos 2 and 3 by A. R. Biggs. Prepared in October, 1997.

Web Site Author: Alan R. Biggs
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