Why Birch trees are “short-lived” in Wisconsin

Birches are a favorite ornamental tree in our area for their bright exfoliating bark and graceful branching structures. You may be more familiar with the white peeling bark of Paper Birch, or the bright whites of European Birch. Maybe you are partial to the salmon-colored shaggy bark and the shiny leaves of the River Birch. No matter which species you have in your yard, you may have been told that the reason your Birch is struggling is because “Birches just don’t live very long”. In a way, this is true, but it’s likely not the reason your Birch is struggling.

Compared to other species of trees, such as Oaks, ginkgoes, and Pines, which can live for centuries, Birches do have shorter lives. There are Coastal Redwoods in California that are over 1000 years old. Bur Oaks can live to 600 years old in the right conditions. Even the state tree of Wisconsin, the Sugar Maple, can live 300-400 years old. In comparison, Birches only living 75 – 150 years is a shorter lifespan. But, don’t be fooled into thinking that your 30-year-old Birch is just dying of old age and that there is nothing you can do. A healthy Birch tree should be able to thrive for at least 40-50 years in a typical yard when properly taken care of.

Most Birches’ native habitats is in a forest, near a body of water, surrounded by the canopy of other trees. They thrive in cool, rich, moist soils, which can be hard to find in urban conditions, where they are planted in grass lawns and near building and concrete. In our yards, they compete with turfgrass for water and nutrients, and the exposed ground around them dries up and is easily compacted. Birches are also much more susceptible to drought conditions when planted out in open yards. This puts Birches in a predisposed state of stress which leaves them vulnerable to birch tree diseases and local pests, the most notorious of those being Bronze Birch Borer.

Bronze Birch Borer (Agrilus anxius) is a wood boring beetle that is native to our area. They cause damage to Birches when the larvae hatch and eat the tree’s vascular tissues under the bark. Infestations typically begin in the upper-most portions of the canopy. Each year, the larvae then work their way down until they reach the trunk, destroying the tree’s ability to transfer water and nutrients up to its leaves. They also leave behind wandering galleries under the bark, similar to Emerald Ash Borer. You will first notice small branches dying back, starting in the upper canopy. Once the borers reach the trunk, they can kill whole trees. If left untreated, Bronze Birch Borer (BBB) can kill mature Birches in 3-4 years. Once the larvae pupate and become adults, they exit through the bark, leaving behind small D-shaped holes.

Adults are about a half of an inch long and look greenish- or blueish-black with a bronze metallic sheen. The larvae are white and slender with dark brown jaws. Adults emerge from the bark starting in late May into July, and live for about 3 week. They lay their eggs in Summer, which then hatch in about 2 weeks. Larvae begin feeding in late Summer/early Fall, then overwinter just under the bark. The larvae then pupate the following Spring and the cycle begins again.

Not all Birches are equal to the Bronze Birch Borer. Beetles will specifically target Birches that are already stressed by other environmental factors. This is why it is important to plant your Birch in a location where it experiences proper conditions. Some species of Birches are more susceptible to BBB attacks as well. European White Birch, Paperbark Birch, and many of the stylish introduced cultivars of Birch tend to be more susceptible to attach than our native Birches. There are two cultivars of WI native Birches that show great resistance to attack: Whitespire Birch (Betula populifolia ‘Whitespire”) and Heritage River Birch (Betula nigra ‘Cully’) rarely succumb to BBB attacks. Remember that resistance does not mean immunity. Any Birch that is sufficiently stressed by soil compaction or a lack of water can struggle with BBB.

Try to avoid Bronze Birch Borer in the first place by picking the right tree for the right place. Plant Birches near water sources, or in areas that naturally get more water. Make sure to provide supplemental during dry spells. If you suspect that your Birch has Bronze Birch Borer, call Tree Health Management for a treatment plan. If caught early in an infestation, BBB can be treated with a soil injection of a systemic insecticide called imidacloprid. This is an annual soil injection that translocates throughout the tree’s vascular system. Applications are administered in early Spring and early Fall for best control. If a Birch already has more substantial damage form borers, your arborist may instead recommend a trunk injection of an insecticide called emamectin benzoate. Trees where the BBB has already moved into the trunk may sometimes be too damaged to be able to uptake any insecticides. One of our ISA Certified Arborists will able to assess your Birch and determine what the best course of action is.