Cereals: Pythium Root Rot

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: Pythium Root Rot
6. Related links...

Incidence

Pythium root rot damage on wheat is common in Ontario and is one of the primary seedling diseases of small grains. There are several species of Pythium that attack small grains and, although Pythium is present in all soil types, losses are greatest in cold, wet, clay soils. Pythium (like Phytophthora) is a "water mould" that thrives under wet, saturated conditions and therefore, infection is very dependent on soil moisture and the clay content of the soil. The wetter the soil and the higher the clay content, the greater the potential for infection. Pythium produces mobile spores that migrate through the water film in the soil.

Appearance

Although infection occurs in the embryo 1 or 2 days after planting, seedlings are rarely killed. Infected plants appear stunted with small, pale green-to-yellowish leaves; this is often incorrectly identified as a nutrient deficiency. These symptoms often go unnoticed until spring when non-infected plants begin to grow rapidly. Infected roots are light brown with few or no root hairs. Infection begins at the root tips and disintegrates root hairs and the fine lateral roots, which are critical for nutrient uptake. Affected plants often occur in patches with a general unhealthy appearance. Severely infected plants may break at the soil line.

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Disease Cycle

The fungi survive in the soil and crop residues. They produce spores (zoospores) that swim through moisture films on soil particles and invade the wheat roots. Some species are most damaging in warm soils, while others prefer cold soils. The disease is less severe when phosphate levels are adequate for good root growth.

Management Strategies

Minimize soil compaction and remove excess moisture through increased drainage. Seed treatments containing metalaxyl or metalaxyl-M can reduce infection. Delay planting until conditions will result in a rapid and uniform emergence. For more information on fungicides, refer to OMAFRA Publication 812, Field Crop Protection Guide. (Order OMAFRA Publication 812)

Updates on Cereals: Pythium Root Rot

• Field Crop Protection Guide - Publication 812
  • Cereals: Wheat: Pythium Damping Off

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Related links...

• Diseases
• Cereals

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