Symptoms on leaves may vary from brown spots that lack a halo, to dark brown or black spots with bright yellow halos that look very similar to those of bacterial speck. The leaf spots from syringae leaf spot can be larger than those of bacterial speck. However, it is necessary to isolate the bacterium and conduct laboratory tests to determine which pathogen is involved.

The bacterium is known to survive on both host and non-host plants in a non-parasitic state, and can spread from these plants when cool and wet environmental conditions favor disease development. Wounding is required for infection and the pathogen may invade lesions already caused by another disease. The causal bacterium is a weak pathogen, and the overall disease development may be less than that caused by bacterial speck.

Control may be obtained with copper sprays, but with this disease, spraying is usually not necessary since economic damage is not common. If disease occurs, it should be determined whether the symptoms are caused by syringae leaf spot and not by another bacterial disease which might require more stringent control.