Bacterial Shot hole

• Shot hole is a common ailment of most Prunus species, including cherry laurels. This disease is characterized by the emergence of dark red and brown patches on the surface of leaves. The symptoms of this condition are attributed to the growth of two related bacteria, Xanthomonas pruni and X. campestris. As the disease progresses, the discolored spots rot away and leave jagged tears or holes in the plant's foliage. Symptoms of bacterial shot hole are similar to diseases caused by several fungal agents, making it difficult to definitively diagnose the cause of leaf damage.
  
  

Cercospora Leaf Spot

• Leaf spot diseases on cherry laurel are caused by several genera of fungi, including Cercospora and Blumeriella. Initial symptoms of a Cercospora infection include reddish purple or brown legions scattered across the surface of leaves. According to the University of Arkansas, moisture from rain and overhead irrigation are closely associated with the severity of this disease. Cercospora spores are dispersed by wind and water, which allows them to spread across an entire plant and to neighboring plants quickly. Damage caused by fungal leaf spot diseases are unsightly, but are rarely serious enough to kill the tree.
  
  

Fire Blight

• Fire blight is a devastating disease caused by the Erwinia amylovora bacteria. It affects a variety of trees, including apples (Malus spp.), firethorn (Pyracantha spp.) and cherry laurel. Fire blight impacts nearly all of the living tissues of its host plant, including twigs, leaves, flowers and bark. Green growth wilts and decays quickly upon infection. The bacteria spreads from the vulnerable green growth to the branches and trunk, creating distorted growths called cankers. Cankers house large colonies of bacteria, allowing them to overwinter in safety. Bark and wood infected with fire blight bacteria turns to a bright shade of red or orange.
  
  

Control and Prevention

• Controlling bacterial diseases tends to be more difficult than treating fungal ailments. According to the University of California, there are a small number of chemicals available to domestic growers to treat fire blight, but they are largely unsuccessful at curing serious infections. Fungal diseases, like Cercospora leaf spot, are more manageable. Removing infected leaves and clearing out all fallen plant debris prevents the fungus from surviving through the winter. Fungicide can also be applied to treat a large outbreak. Pruning can be used to manage limited infections of bacterial diseases by removing all infected growth, particularly branches and twigs inflicted with cankers.