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.
Xytect can be applied to the soil in late summer/fall for the following season or 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 kill 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.
Beetles may appear to return after treatment because insecticides may not work on the eggs and additional eggs hatch into larvae after treatment.
Signs of Damage
- Look for black to greenish blue adult beetles, and holes from their feeding on new leaves in May
- Clusters of oval, glossy, pale-yellow eggs may be found on the undersides of leaves in May
- These eggs hatch into small black larvae, which cause damage by feeding in groups on the leaf tissue between the veins
Photo: U of MN Plant Diagnostic Lab
Trees At Risk
- Pin oak
- Willow oak
- Adults emerge in April and May (192-488 GDD) 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.
- The adult beetles seek protection under loose bark or piles of leaves in August and September where they overwinter.
A Treatment 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 of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments by forestryimages.org