The bronze birch borer is a native insect that can weaken and kill birches in landscape plantings. While trees that are stressed by dry soil are most vulnerable, different species of birches have been noted to have varying susceptibility to this pest.
Some of the popular non-native birches used in landscapes, such as the European white birch (Betula pendula), show quite a lot of vulnerability to borer infestation. But the monarch birch (Betula maximowicziana) has often been touted as having good resistance. A newly-completed, long-term field trial conducted at Ohio State University has shown that this is not the case.
In an assessment of birches planted in 1979, most of the monarch birches and all of the other non-native species (B. pendula, B. pubescens, and B. szechuanica) had died from borer infestation within a few years of planting. But twenty years after planting, 97 percent of river birch (B. nigra), 76 percent of paper birch (B. papyrifera) and 73 percent of 'Whitespire' gray birch (B. populifolia), all native species, were still alive.
These results suggest that monarch birch should be considered as vulnerable as other non-native species to the borer and that in terms of resistance, river birch (pictured) is the most problem-free choice for most landscape uses.
To read the entire study, go to: Environmental Entomology.
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