The causal bacterial pathogen, Pantoea stewartii subsp. stewartii (syn. Erwinia stewartii), survives overwinter inside the corn flea beetle which is the primary vector moving bacteria into corn plants. This bacterium can also be seedborne, but the rate of transmission from seed to growing seedling is very low (at most 0.02%).
This disease no longer occurs commonly in the USA. It was last confirmed on Long Island in 2000. Resistant varieties provide effective control. There are also resistant field corn varieties which reduce amount of inoculum in the region. In addition, conventional seed is now routinely treated with insecticide that kills corn flea beetles before they can transmit bacteria to corn plants.
Characteristic foliar symptom of Stewart’s wilt is long, pale green to yellow streaks that develop parallel to leaf veins, can have a wavy appearance, and can extend most of the length of the leaf. These streaks start where corn flea beetles harboring bacteria fed on the leaf. They turn light brown as affected leaves die.
Bacteria ooze out of veins when a cut is made across the yellow streak and the leaf piece is put in water. This bacterial streaming can be seen with a compound microscope. For bacterial pathogen such as this one that stream, not all do, looking for streaming is a fast, easy, cheap way to make a diagnosis, in this case determining if yellow streak symptoms are Stewart’s wilt. The following images show a lot of bacteria that streamed out of these leaf pieces. Approximately ¼-inch wide rectangular leaf pieces were put on a microscope slide in a drop of water, then examined. Phase contrast was used for the second image which is why the background is dark and the bacteria are white.
When disease onset occurs during the seedling stage, infection is systemic and affected corn plants wilt and can be killed.
Older plants affected by Stewart’s wilt look like they are affected by drought.
Ear quality can be affected.
