River Birch is a great landscape tree that adapts well to both wet and dry sites. It is favored for its attractive exfoliating bark. It has only a few pest issues. Currently one is active causing new leaves to become distorted and corrugated-like. This is caused by an aphid with a peculiar name, the spiny witch-hazel gall aphid; so named because it spends part of its life on witch-hazel and part on birch.
Examining under the puckered leaves will reveal these pesky aphids and a white granular material they pack into the voids. The aphids also produce honeydew, which falls on things underneath the river birch tree. It can also attract ants who are coming to harvest the honeydew. The leaves attacked by the aphid eventually turn brown and drop from the tree. Fortunately, they produce another flush of leaves and the tree suffers no real harm.
Very little damage is caused by this aphid. Occasionally the population can be so high some smaller branches may die back. If treatment is required, consider systemic insecticides applied to the soil beneath the tree. These products are very effective against aphids.
Always read the label carefully before purchasing a pesticide being sure that it lists the host plant and the insect. Be sure to follow all label directions exactly.
Source: Clemson Extension EIIS/TO-17
Kelly R. Jackson is the Christian County Extension Agent for horticulture. He can be reached at 270-886-6328 or visit Christian County Horticulture online at www.christiancountyextension.com.