Willow Leaf Beetle Diagnostic Guide
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.
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.
- 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.
- 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.
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.
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
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