Leaf Damage on Betula Pendula Youngii

Sooty Mold

• Aphids (Aphis spp.) suck the juices from tender stems and leaves and excrete a sticky substance known as honeydew. This substance attracts sooty mold, caused by several species of fungi. This black, powdery mold doesn’t actually harm the weeping birch unless it is present to such a large degree that it prevents the tree from carrying out photosynthesis. The best approach to control sooty mold is to rid the tree of the aphid infestation. A strong blast of water from a hose will dislodge them and knock them from the tree.

Birch Leafminer

• Closely related to wasps, the female birch leafminer (Fenusa pusilla) cuts slits in leaves in which to deposit her eggs. When the eggs hatch, the wormlike larvae feed on the leaves’ interiors, leaving mines behind. Initial symptoms aren’t easily recognizable, so it isn’t until the tree turns brown that most people understand there is a problem. As long as the damage doesn’t extend over 30 percent of the tree, it will recover. Treatment isn’t required for the health of the tree.

Birch Skeletonizer

• The best way to determine if your European weeping birch is infested with birch leafminer or birch skeletonizer (Bucculatrix canadensisella Chambers) is by the shape of the mines. The birch leafminer’s tunnels are kidney-shaped, while the skeletonizer’s are serpentine. The latter cause brown foliage that drops prematurely from the tree. Chemical control isn’t necessary, according to foresters with the Vermont Department of Forests, Parks and Recreation. Raking and burning fallen leaves helps reduce birch skeletonizer populations.

Bronze Birch Borer

• A beetle with a metallic appearance, the bronze birch borer (Agrilus anxius Gory) feeds on the weeping European birch’s leaves before laying its eggs beneath the tree’s bark. When the grubs emerge, they feed in the cambium – the area between the inner bark, the phloem and the wood or xylem. They feed in a zigzag pattern, causing permanent damage to the phloem tissue. Typically, the first indication of an infestation is the sudden wilting and death of a part of the tree, usually the crown. Treatment is challenging and requires the injection of insecticides such as permethrin into the tree. Prevention is far easier and requires keeping the tree healthy. Eight to 18 inches of water delivered slowly once a week, a 2- to 4-inch layer of mulch over the root system and avoiding pruning the tree when borers are in flight in your region will go a long way in protecting the weeping European birch.