Cereals: Snow Moulds

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: Snow Moulds
6. Related links...

Incidence

Although snow moulds do require specific environmental conditions, they occur most ears to some degree. Severity increases in years when an early snow cover in the fall (mid-November) persists until late March or April.

Appearance

Snow mould symptoms appear soon after snow melt. Individual plants, groups of plants or large areas can be affected. The most obvious symptom is dead plants that are slimy, brown and rotted.

Plate 111. Snow mould appears when the snow melts after long periods of snow cover. Dead plants are slimy, brown and rotted.

Early-planted wheat is usually affected since lush "top-growth" promotes infection and aids in disease spread from plant to plant. Plants that have not been killed (i.e., have a healthy crown) may have one or many leaves that are totally or partly necrotic (i.e., have brown tips). Symptoms are most pronounced in areas of the field that had heavy snow cover, such as field borders, headlands and down slopes of hills. Typical winter injury on wheat due to other causes will most often occur in areas that had no snow or were covered in ice. Symptoms are pronounced in fields planted with poor-quality or untreated seed. Warm, dry weather in the spring will stop disease development and promote rapid plant growth. Plants with considerable damage often recover from the disease with little or no impact on yield.

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Disease Cycle

The group of fungi that cause snow moulds are temperature tolerant and will grow under heavy snow cover. Snow deeper than 30 cm will insulate the soil, preventing it from freezing while maintaining a soil surface temperature at or just above 0°C (32°F). Under these conditions, photosynthesis is significantly reduced, and the developing wheat plant has no choice but to use its stored carbohydrates and proteins to survive. The result is a stressed plant that is more susceptible to diseases, especially snow moulds.

Management Strategies

Although no winter wheat cultivars are resistant to the disease, they do differ in tolerance. Seed treatments are very effective against snow moulds but they must be applied on the seed and good seed coverage is essential. In years when snow mould causes substantial reductions in stands, replant to a spring grain or soybean crop. The disease does not affect spring-planted grain.

Updates on Cereals: Snow Moulds

No updates available at this time.

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Related links...

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

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