Bacterial leaf blight

Bacterial leaf blight occurs when the tree is in soil that is too moist.

Also known as:
Bacterial blight (Peony)
Bacterial leaf spot
Walnut blight (Xanthomonas campestris juglandis)
Black rot (crucifers)

Recognize bacterial leaf blight
Bacterial leaf blight, photo: Ninjatacoshell - CC BY-SA 3.0

Bacterial leaf blight (Xanthomonas campestris ssp.). Bacterial leaf blight occurs when the tree or shrub is in soil that is too wet. Summertime high temperatures with high relative humidity encourage bacterial leaf blight. The bacteria overwinter in the buds.
Bacterial leaf blight spreads through raindrops and wind. The bacteria enter the plant through stomata or through damage. Rain plays an important role in this process.
Confusion with leaf burn from over-fertilization should be ruled out.

Affected plants


Cut away and destroy infested leaves. Do not throw these on the compost pile to prevent a new source of infection.


Not pruning helps prevent bacterial leaf blight.