Control Plant Diseases
For Better Farming And Better Living Mimeo BP 5-11 Revised

BACTERIAL WILT OF CORN

Bacterial wilt, or Stewart's disease, is one of the most important diesases affecting
sweet corn.

The bacterium causing this disease overwinters in the bodies of corn flea beetles. When
the adult beetles begin to feed on young corn seedlings in late spring and early summer,
bacterial wilt infections start on the leaves. During the growing season these beetles con-
tinue to spread the disease from infected to healthy plants.

The prevalence and severity of Stewart's wilt varies from year to year, and is
apparently related to the number of flea beetles that survive the winter months. During
mild winters a large number of corn flea beetles will usually survive. As a result, the
disease is abundant the next summer. Cold winters reduce flea beetle populations, and
there are fewer of them to spread infection. Bacterial wilt has not been a serious problem
on sweet corn in recent years.

Symptoms of Bacterial Wilt

In sweet corn, susceptible varieties and hybrids wilt rapidly and resemble plants
with an inadequate water supply. Infected plants that do not die are stunted, tassel pre-
maturely, and may produce no ears. In the early stages of the disease infected plants
frequently show long, irregular, pale green to yellowish streaks in the leaves. Eventually
the vascular bundles in the entire plant become filled with bacteria so that when the stalks
are cut, yellow masses of the organisms ooze out and form beads on the cut surface. If
small pieces of infected leaves are placed in a drop of water and observed through a
microscope, clouds of bacteria flow from the cut ends of the vascular bundles. In severely
infected plants, cavities may form in the pith of the stalk.

Dent corn is generally more resistant than sweet corn. Seldom does the disease
spread through the entire dent corn plant, but in some very susceptible inbred lines it
may In such instances, the symptoms resemble those found in sweet corn. In dent corn,
the characteristic symptom is the long, irregular, pale green streaks in the leaves that
eventually turn yellow, or straw-colored, and then die.

Cause of Bacterial Wilt?

Bacterial wilt of corn is caused by a bacterium, Xanthomonas stewartii. These
bacteria enter corn plants through wounds in the leaves, made chiefly by corn flea beetles.

PURDUE UNIVERSITY Agricultural Extension Service, Lafayette, Indiana
Department of Botany and Plant Pathology, Life Science Building