Stewart's Wilt - Hosts and Symptoms

Hosts and Symptoms

Stewart's wilt can be a serious disease of many corn types, including: sweet, dent, flint, flower, and popcorn. Sweet corn and popcorn cultivars are more susceptible to Stewart's wilt than field (dent) corn, but there are some dent corn inbreds and hybrids that are susceptible. Stewart's wilt causes yield reductions by decreasing the size of corn stand or by limiting the production of corn. This results in fewer and smaller ears of corn.

Stewart’s wilt has two phases of symptoms: the wilt phase and the leaf blight phase. For both phases, symptoms first appear as leaf lesions, initiating from corn flea beetle feeding scars. At first, the leaf lesions appear long and irregularly shaped and are light green to yellow and later on, straw colored. On mature plants, yellowish streaks with wavy margins extend along the leaf veins. This leaf blight phase is often prevalent after tasseling and the symptoms look similar to frost damage, drought, nutrient disorders, northern corn leaf blight (caused by Exserohilum turcicum), and particularly Goss's wilt (caused by Clavibacter michiganensis ssp. nebraskensis). A good way to determine if the corn is facing symptoms from Stewart's wilt, is to look at the leaf tissue under microscope. If the bacterial ooze exhibits nonflagellate, non-spore-forming, rod-shaped bacterium, there is a great chance it's Stewart's wilt.

The corn flea beetle feeds on corn leaf tissue and then transmits the bacteria, Pantoea stewartii, into the plant. When large populations of corn flea beetles are feeding, skeletonization of leaves and death of seedlings can occur.

In most cases, the wilt phase occurs on seedlings, but for certain corn types (i.e. sweet corn) more mature plants can become wilted. The wilt phase is systemic, meaning the majority of the plant is infected via bacterial movement and colonization of the plant's vascular system. When the bacterium spreads within the plant, leaves begin withering and can die. Plants become stunted and at times, the whole plant may wilt and die. Dwarfed, bleached tassels are common. Often, plants that have wilt symptoms will also have leaf blight symptoms.

When the bacteria reach the corn stalks, the vascular bundles become brown and necrotic. A good indicator of whether or not the bacteria has infected the stalks is if there are yellow masses of bacteria oozing from the vascular bundles. With certain sweet corn hybrids, yellow, slimy ooze collect on the inner ear husks and/or cover the corn kernels. It is possible that the kernels may also have grayish lesions with dark margins or they may be irregular in shape and dwarfed. Another common symptom of the bacteria is formation of open cavities within the stalk tissue. While the plants are weak and vulnerable, stalk rot fungi can further invade the corn plant.