Corn: Bacterial Leaf Blight or Wilt (Stewart's Wilt)

Excerpt from Agronomy Guide for Field Crops (Chapter 3)

Order OMAFRA Publication 811: Agronomy Guide for Field Crops

Table of Contents

1. Incidence
2. Appearance
3. Disease Cycle
4. Management Strategies
5. Updates on Corn: Bacterial Leaf Blight or Wilt (Stewart's Wilt)
6. Related links...

Incidence

Although bacterial leaf blight occurs throughout Ontario, the disease is a major concern in Southwestern Ontario. Essex and Kent counties, where the majority of seed corn production fields are located, tend to be especially affected by bacterial leaf blight. Warmer-than-normal winters in this area have allowed the corn flea beetle, which vectors bacterial leaf blight (Stewart's wilt), to survive in higher numbers.

Appearance

There are two distinct phases of the disease that occur in Ontario, the late phase and the wilt phase. The wilt phase affects primarily highly susceptible seed corn inbreds and sweet corn hybrids early in the year (V2 to V4). The first noticeable sign of the disease appears as long, yellow streaks that extend along the length of the leaf. These streaks will take on a water-soaked appearance and eventually become brown, dead streaks (necrotic). The bacteria interrupt the water and nutrient movement in the plant by plugging the vascular system of the plant. The result is a rapid wilting and even death. Since the new growth is affected, the wilting and death occur from the top down. Cutting the plant lengthwise will reveal a discoloured, rotted or hollowed-out growing point.

Plate 28. Stewart's wilt (bacterial leaf blight) occurs after tasselling. Wilt phase occurs at V2 to V4 stage. Bacteria vectored by corn flea beetle.

The leaf blight phase or late-infection stage often occurs after tasselling and is the most common. Symptoms include pale green to yellow streaks with irregular or wavy margins that run parallel to the veins. These streaks may run the full length of the leaf. Infected leaves eventually become dry and brown. Often corn flea beetle-feeding marks are visible within the lesions. Premature leaf death can result in reduced yield and an increase in stalk rots since weakened plants are more susceptible to stalk rots.

Disease Cycle

The bacteria overwinters in the gut of adult flea beetles, which hide through the winter in protected areas. Mild winters can result in higher beetle numbers. Overwintering adult flea beetles feed on corn in the seedling-to-whorl stage, and susceptible varieties will develop a stem wilt resulting in complete plant loss. This occurs rarely in hybrids but occasionally in susceptible seed corn parents. The next generation of adult beetles emerges after corn silking and causes leaf wilting symptoms, which are commonly seen in many hybrids. Seed transmission is rare. Most often, late infections after silking are associated with high beetle populations. Sweet corn is often more susceptible than field corn and can serve as a reservoir for the bacteria. The disease is often found in the best fields, and fertility seems to play a part. Susceptibility to the disease increases in fields that have high nitrogen and phosphorous levels.

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Management Strategies

Field corn has good tolerance to Stewart's wilt and therefore no control is required, but certain seed corn inbreds are susceptible and are rated for disease tolerance. This disease is controlled by managing the corn flea beetle. For further management information, see the section Corn Flea Beetles.

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Updates on Corn: Bacterial Leaf Blight or Wilt (Stewart's Wilt)

No updates available at this time.

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Related links...

• Diseases
• Corn
• Field Crop Protection Guide - Publication 812

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