Cereals: Leaf and Stem Rust

Excerpt from Agronomy Guide for Field Crops (Chapter 6)

Order OMAFRA Publication 811: Agronomy Guide for Field Crop

Table of Contents

1. Incidence
2. Appearance
3. Disease Cycle
4. Management Strategies
5. Updates on Cereals: Leaf and Stem Rust
6. Related links...

Incidence

There are various species of rust that cause disease on wheat and barley. Leaf and stem rust occur in all regions of Ontario every year. Stem rust may be a serious problem when small grains are grown near the common barberry bush. Of the two rust diseases, leaf rust continues to pose the biggest threat to small grain production.

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Appearance

Leaf rust affects the leaf blades and sheath, whereas stem rust can be found on leaves, sheaths, stem and heads. The disease begins as small, yellow-brown spots (pustules) that contain orange-to-orange-brown spores. In most cases, infection is found on the upper surfaces of the leaves and leaf sheath. In severe cases, leaves turn yellow and brown (necrotic). In spring grains, late-planted fields are most likely to show the disease, whereas late-maturing winter wheat may be slightly more at risk.

Plate 112. Leaf rust affects the leaf blades and sheath. Small, yellow-brown spots contain orange to orange-brown spores.

Stem rust begins as dark reddish-brown spots on both sides of the leaves, stems and heads (see Plate 113 on page 294). When developed, spots will rupture through the surface releasing spores into the air. The surface of the tissue appears ragged and torn.

Plate 113. Stem rust can be found on the leaf, sheath, stem and head.

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Disease Cycle

Common barberry is necessary for the stem rust fungus to complete its lifecycle. Leaf rust, on the other hand, does not overwinter in the province but is blown into Ontario on southerly storm fronts from infected plants in the Southern United States and Mexico wheat regions. In most years, leaf rust spores arrive late (after flowering), resulting in little economic impact. These diseases are most severe when warm temperatures (20°C-28°C or 68°F-82°F in day, 16°C-22°C or 61°F-72°F at night) and frequent dews occur when the crop is at the flag leaf (Zadok's 37) to flowering (Zadok's 61-71) stages.

Management Strategies

Removing the alternate host, common barberry, will reduce stem rust. Use tolerant varieties when possible. Since leaf rust usually appears on the upper two leaves first, it is important when scouting for rust to check the second leaf from the top prior to head emergence, and the flag leaf during head emergence for signs of disease. Use foliar fungicide treatments when the flag leaf has 5-10 pustules or 1% of the flag leaf area is affected (during head emergence to the end of flowering) and the weather forecast predicts rainy, wet weather. Planting spring grains early allows plants to mature before inoculum levels become heavy. In oats, crown (leaf) rust is dependent on European buckthorn as the alternate host. Remove or destroy buckthorn. Refer to the OMAFRA Publication 812, Field Crop Protection Guide, for fungicide treatment recommendations.

Updates on Cereals: Leaf & Stem Rust

• Field Crop Protection Guide - Publication 812
  • Cereals: Wheat: Rust (Leaf and Stem)
  • Cereals: Wheat: Stripe Rust
  • Cereals: Barley: Rust (Leaf and Stem)
  • Cereals: Oats: Crown (Leaf) Rust
  • Cereals: Rye: Leaf Rust

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Related links...

• Diseases
• Cereals

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