Over the next few days, you may find yourself wondering “what is he doing to that tree? Is he injecting it with something?” We don’t often think of trees needing check-ups or medical treatment, but sometimes they need just that.
One of the diseases of trees that we deal with here on campus is called bacterial leaf scorch (Xylella fastidiosoa), or BLS for short. BLS is a bacterial infection that multiple species of plants can catch, and it is transmitted primarily by an insect called the Leafhopper (Homalodisca vitripennis). Leafhoppers feed on the water-moving xylem of plants, which in turn can spread BLS from tree to tree.
BLS infections are most commonly noticed in oaks in the red oak group during the late summer. However, they can be found in many other species and the list is growing every year. As of 2020, there were 595 different plant species susceptible to BLS.
The infection results in the plugging up of the tree’s xylem which prevents water from moving efficiently throughout its vascular system. This leads to the leaves of the plant taking on a “scorched” look, as the lack of water stresses its health. This is normally not enough to kill a tree outright, but the tree will slowly decline year after year until it needs to be removed. Often, this can predispose the tree to secondary pathogens as well.
These symptoms can look almost identical a tree that has been over-fertilized or drought stressed, so it is very important to get a diagnosis of BLS before considering treatment options. So how do we treat it? Roughly the same as if you get a bacterial infection: With antibiotics.
By injecting the tree with the correct amount of oxytetracycline at the correct time of year, we can either suppress current year symptoms or prevent them from occurring the following year. Notice that it said “suppress” symptoms there, and not cure them. There are unfortunately no treatments that can completely cure the tree of the BLS infection, and it must be treated year after year to continue protection. This is again why it’s so important to have a correct diagnosis before you begin. Just as we worry about antibiotic resistance for human diseases, we want to be sure we don’t cause the same issue with our plants.
So if you see someone injecting a tree on campus this month, just think of it as a booster shot in the Arboretum’s plant health care program.