Bacterial leaf scorch (BLS) was discussed in issue no. 13 of this newsletter. In that article, I stated that symptoms appear in mid- to late summer. We are seeing symptoms of this disease very clearly now on a few oaks in the Champaign-Urbana area. Learn the symptoms of this disease and take another look at your problem oaks, elm, hackberry, maple, mulberry, sweetgum, sycamore, and planetree. We have confirmed BLS only on oaks in Illinois, but it could also occur on these other hosts.
Symptoms of BLS on oaks include early leaf browning, sometimes appearing along leaf margins but often in scattered blotches. We have seen this necrosis on old leaves and new leaves alike, scattered throughout the tree. The differences between symptoms of this disease and environmental scorch are twofold. BLS appears in mid- to late summer. Environmental leaf scorch usually appears in the spring, or as soon as hot, dry conditions begin. New leaves emerge each spring looking healthy whether the problem is BLS or environmental scorch. BLS becomes increasingly more severe with each summer, resulting in the death of the tree in 4 to 6 years. Environmental scorch does not kill trees.