Corn Leaf Diseases: Common Rust

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. Management Strategies
4. Updates on Corn Leaf Diseases: Common Rust
5. Related links...

Incidence

Common rust does not overwinter in Ontario but instead originates from infected corn in the southern United States and Mexico. Rust spores are blown into Ontario from these infected corn plants. In most years, rust is of minor economic importance, however sometimes spring storm fronts bring in spores and cause early season infection. The disease is favoured by high humidity with cool evening temperatures (14°C-18°C) followed by moderate daytime temperatures.

Appearance

Early symptoms of rust infection are yellow flecks or spots on either side of leaf. These develop into small, brick-red pustules that break through the surface (epidermis). The brick-red colour is the result of spores being released from these oval or elongated lesions (2-10 mm (1-4 in.) long). Yellowing of the leaf occurs around these lesions. Dead, brown (necrotic) areas of the leaf develop, and in severe cases the entire leaf dies. The brick-red spores mature and turn black as they mature, causing the lesions and leaf surface to appear black.

Plate 29. Common rust symptoms range from yellow flecks to red pustules.

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Management Strategies

Since common rust does not survive in Ontario, cultural practices such as reduced tillage and crop rotation do not influence disease development. Commercial corn hybrids have good tolerance, whereas many seed corn inbreds, sweet corn and speciality corn hybrids are very susceptible to the disease. Foliar fungicides in field corn are not usually needed but can be economical in highly susceptible seed corn inbreds or specialty corn hybrids.

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Updates on Corn Leaf Diseases: Common Rust

• Field Crop Protection Guide - Publication 812
  • Corn: Rust

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Related links...

• Diseases
• Corn

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