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Two-Lined Chestnut Borer Diagnostic Guide

Agrilus bilineatus

Two-lined Chestnut Borer (TLCB) is an opportunistic insect pest that attacks a variety of species. It was given the name “chestnut” borer in recognition of its status as a primary pest of the American chestnut tree. The chestnut has been almost completely wiped out by a fungal disease, yet the insect has retained its name to this day even though there are few chestnut trees for it to attack. A pair of faint white to golden colored lines on the main body and wings of adults are useful identifiers.

Trees at Risk

The two-lined chestnut borer is primarily a pest of Quercus and Castanea species. It is considered one of the most serious insect pests on oaks, and the species most frequently attacked are chestnut, white, black, red, scarlet, and bur oaks.

Black Oak

Bur Oak

Red Oak

White Oak

Signs of Damage

  • Larvae create meandering galleries in the phloem, which are visible if patches of bark are cut from infested branches or stems.
  • Impaired water movement within infested trees causes leaf wilting and dieback from the top of the tree downward. There is a “dead, red, green” appearance from the top down (i.e. dead leaves, wilting leaves, and green leaves).
  • The dead, brown leaves usually remain attached to the tree, even after normal leaf drop in the fall.

Two-Lined Chestnut Borer SignsTwo-Lined Chestnut Borer Signs

Physical Appearance

  • The larvae are white with an enlarged head, slender, noticeably segmented, flattened, and about 2.5 cm. long when fully grown.
  • Larvae have two spines at the tip of their abdomens.
  • Beetles are 6-10 mm in length and approximately 2 mm in width.
  • Adults are bluish-black in color.
  • This pest gets its name from the two pale lines which run the length of the wing covers.
  • Adults emerge through D-shaped exit holes, and generally begin to appear in early June.

Two-Lined Chestnut BorerTwo-Lined Chestnut Borer Larvae

Treatment Strategy

The best protection from the two-lined chestnut borer is prevention. This pest attacks weakened and stressed trees, so attention should be given to maintaining tree health by watering during drought, mulching, and minimizing damage to the root zone that could cause root injury and stress. When symptoms of Two-lined chestnut borer are visible it is nearly impossible to save the infected limbs, so consider whether the remaining portions of the canopy are worth trying to preserve. As a rule of thumb, if more than a third of the canopy is infested the chances of saving the tree are significantly reduced. Infested branches and deadwood should be removed, so give attention to what the tree will look like before deciding on subsequent treatments. High value trees at risk for infestation by the Two-lined chestnut borer may be treated preventatively with Xytect™ insecticide. A soil drench in the fall or early spring will provide season-long protection. Additional protection can be obtained through cover sprays of insecticides to the trunk and main limbs. Trees infested with Two-lined chestnut borer may be similarly treated, although trees with serious decline are unlikely to be saved.

Emamectin benzoate by Tree Injection is also a good option and is effective for 1-2 years.

  • Soil Application using Xytect 2F

    Dosage: Trees < 15" DBH 6ml/inch and trees > 15" DBH 9-12 ml/inch.
    Timing: Early spring & late summer/fall until soil freezes
    Re-Treatment: Annually
    Xytect 2F
    Xytect 2F
    $69.60
  • Tree Injection using Xytect 10%

    Dosage: See label – Rates vary with tree size
    Timing: Preventative: Mid-May to Mid-June (only on trees where soil applications are not feasible). Symptomatic: apply once on trees showing early symptoms & follow with annual soil applications of Xytect™.
    Re-Treatment: 1 to 2 years
    Xytect 10%
    Xytect 10%
    $453.96
  • Soil Application using Transtect

    Dosage: 1 packet/5 DBH inches. 6 packets/gallon water (1.5-2.0 oz./inch DBH) for trees < 24 inches DBH. 6-12 packers water (1.5-2.0 oz./inch DBH) for trees > 24 inches DBH.
    Timing: Preventative: Spring (2-3 weeks prior to GDD 550). Symptomatic: Apply once on trees showing early symptoms & follow-up with annual soil applications of Xytect.
    Re-Treatment: Annually
    Transtect
    Transtect
    $326.00
  • Systemic Bark Spray using Transtect

    Dosage: 1 packet/5 DBH inches. 6 packets/gallon water (1.5-2.0 oz./inch DBH) for trees < 24 inches DBH. 6-12 packets/gallon water (1.5-2.0 oz./inch DBH) for trees > 24 inches DBH.
    Timing: Preventative: Spring (2-3 weeks prior to GDD 550) Symptomatic: Apply once on trees showing early symptoms & follow-up with annual soil applications of Xytect.
    Re-Treatment: Annually
    Transtect
    Transtect
    $326.00
  • Soil Application using Xytect 75WSP 22 packets

    Dosage: 1 packet/24 inches of DBH for trees < 15 inches DBH. 1 packet/12 inches of DBH for trees > 15 inches DBH.
    Timing: Early spring & late summer/fall until soil freezes
    Re-Treatment: Annually
    Xytect 75WSP 22 packets
    Xytect 75WSP 22 packets
    $148.00
  • Systemic Bark Spray using BiFen XTS

    Dosage: 6.4-12.8 fl. oz./100 gallons
    Timing: Spray trunk and limbs within a week of the onset adult emergence (GDD 550)
    Re-Treatment: Annually
    BiFen XTS
    BiFen XTS
    $35.16

Treatment Expectations

  • Preventative treatments are most effective. Treat trees preventively if adjacent trees display symptoms from Two-lined chestnut borer attack.
  • If the top third of the tree is showing symptoms, saving the tree is difficult.
  • For infested trees, soil applications of Xytect™ will be effective against the next two-lined chestnut borer generation. An improvement in the tree typically occurs the 2nd full season following treatment as the tree repairs previous damage and prevents future damage.

A Diagnostic Guide is designed to help you identify a pest issue and management solutions. Always refer to product label for all rates and approved uses. Some images courtesy forestryimages.org. Use of the images does not imply endorsement of treatments by forestryimages.org

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