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Willow Leaf Beetle Diagnostic Guide

Plagiodera versicolora

Willow leaf beetle, Plagiodera versicolora, can strip a tree of many leaves in a season, but it is rarely fatal. During the summer, willow leaf beetle adults and larvae chew holes and notches in the leaves of willow trees. The feeding is done on the leaf tissue between the veins, causing a skeletonized appearance. If total browning of the leaves were to occur in two or three consecutive years, this could be serious to the health of the tree.

Trees at Risk

Willow, cottonwood, and poplar.

Cottonwood

Poplar

Willow

Signs of Damage

  • Notches are chewed out of leaves by larvae from May to June.
  • Leaves can be completely devoured leaving behind only the veins.
  • From a distance the tree appears scorched.
  • Severe infestations include brown leaves.

Willow Leaf Beetle

Willow Leaf Beetle

U of MN Plant Diagnostic Lab

Physical Appearance

  • Adults are dark metallic black to greenish-blue and are visible in May.
  • Eggs are oval, glossy, pale yellow and found on the undersides of leaves in May, June, and August.
  • Larvae are black, small, and often found feeding on leaf tissue.

Willow Leaf Beetle

Biology

  • Adults emerge in April and May and begin feeding on willow leaves.
  • Eggs are laid on the undersides of leaves in May and a few days later the young larvae emerge and begin feeding. Second generations begin in June and July and a third generation may occur in some years.
  • In August and September, the adult beetles seek protection under loose bark or piles of leaves, where they overwinter.

Treatment Strategy

Xytect™ can be applied to the soil in late summer/fall for the following season. Spring soil applications of Xytect™ may provide acceptable levels of control if applied early enough in the growing season. Transtect™ can be applied to the soil in early spring to control current year crawlers. If the Xytect™ or Transtect™ treatment timing has already passed, foliar sprays of Up Star Gold™ or RTSA Horticultural Oil™ should be used in June after the willow leaves have fully flattened out. A second spray may be needed 30 days later.

  • Soil Application using Xytect 2F

    Dosage: 6ml/inch of DBH
    Timing: Late summer to early fall
    Re-Treatment: Annually
    Xytect 2F
    Xytect 2F
    $69.60
  • Soil Application using Transtect

    Dosage: 1 packet/5 inches of DBH
    Timing: Early spring
    Re-Treatment: Annually
    Transtect
    Transtect
    $326.00
  • Foliar Spray using Up-Star Gold

    Dosage: 21.7 fl. oz. /100 ga. water
    Timing: June
    Re-Treatment: Annually
    Up-Star Gold
    Up-Star Gold
    $33.33
  • Soil Application using Xytect 75WSP 22 packets

    Dosage: 1 packet/24-48 inches of DBH
    Timing: Fall application for next year control, or early spring application
    Re-Treatment: Annually
    Xytect 75WSP 22 packets
    Xytect 75WSP 22 packets
    $148.00
  • Soil Application using Transtect

    Dosage: 1 packet/5-17 inches of DBH
    Timing: Transtect can be applied to the soil in early spring
    Re-Treatment: Annually
    Transtect
    Transtect
    $326.00
  • Systemic Bark Spray using Transtect

    Dosage: 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: Spring
    Re-Treatment: Annually
    Transtect
    Transtect
    $326.00
  • Soil Application using Lepitect

    Dosage: 0.2-0.4 oz/inch DBH
    Timing: Spring 1-3 weeks before insect feeding
    Re-Treatment: 30 days
    Lepitect
    Lepitect
    $59.20
  • Foliar Spray using RTSA Horticultural Oil

    Dosage: 1 -2.5 oz./gallon
    Timing: Apply RTSA Hort Oil to smother second instars overwintering on dormant twigs. RTSA Hort Oil sprays should be applied to the trunk and branches of a tree in June. 192-448 GDD
    Re-Treatment: Annually
    RTSA Horticultural Oil
    RTSA Horticultural Oil
    $39.00
  • Tree Injection using Xytect 10%

    Dosage: 1 ml/inch DBH for trees 2 to 10 inches DBH
    Timing: Early spring – summer, ideally 1-3 weeks before pests are actively feeding
    Re-Treatment: Annually
    Xytect 10%
    Xytect 10%
    $453.96
  • Tree Injection using Xytect 10%

    Dosage: 1.5 ml/inch DBH for trees 10 to 36 inches DBH
    Timing: Early spring – summer, ideally 1-3 weeks before pests are actively feeding
    Re-Treatment: Annually
    Xytect 10%
    Xytect 10%
    $453.96
  • Tree Injection using Xytect 10%

    Dosage: 2 ml/inch DBH for trees 36 inches DBH and above
    Timing: Early spring – summer, ideally 1-3 weeks before pests are actively feeding
    Re-Treatment: Annually
    Xytect 10%
    Xytect 10%
    $453.96
  • Tree Injection using Xytect 10%

    Dosage: For heavier infestation and/or more resistant insects, use 1.5 ml or 2 ml rates on trees having a DBH of 2 inches and above.
    Timing: Early spring – summer, ideally 1-3 weeks before pests are actively feeding
    Re-Treatment: Annually
    Xytect 10%
    Xytect 10%
    $453.96

Treatment Expectations

Beetles may appear to return after treatment because insecticides may not be effective on eggs and additional eggs hatch into larvae after treatment.

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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