The streaked portions of the leaves quickly die and turn brown. The bacterium spreads systemically in the plants through the vascular system. Severely affected plants wither and die. The disease on field corn usually consists of the late season leaf blight. The bacterium usually does not become systemic in these plants, but is restricted to the leaf lesions.
Yield is reduced by the loss of leaves.
Stalk piths may become deteriorated in severe cases. Plants with Stewart's disease are more susceptible to stalk rots caused by other pathogens. A system has been used to predict the severity of Stewart's disease. The system was based on the influence of winter temperature on the survival of the corn flea beetle, Chaetocnema pulicaria. Erwinia stewartii overwinters in the gut of this insect.