Cereals: Take-All

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: Take-All
6. Related links...

Incidence

There are two closely related fungi that cause take-all in Ontario. The first infects wheat, barley, rye and various grasses, whereas the second is a problem on oats and turfgrasses.

Appearance

Take-all usually becomes noticeable at the heading stage when the heads, stems and leaves of badly affected plants become prematurely bleached.

Plate 109. Take-all is noticeable at heading. Head, stem and leaves all become bleached due to this root disease.

The bleaching of tillers takes only 2 or 3 days. Affected plants occur in circular patches, one to several metres across, or as individuals or small clusters scattered across the field. Many plants appear moderately to severely stunted and bear few tillers. The bleached heads (whiteheads or deadheads) normally are sterile and usually appear 3-5 weeks before harvest. Whiteheads may also be caused by factors other than take-all. Dark-coloured moulds tend to grow on the whiteheads, especially in damp weather. The conspicuous bleaching is secondary to disease on the roots, crown and lower stem.

The roots of diseased plants are sparse, blackened and brittle. The dark-coloured rot often extends to the crown and basal stem. Removal of the lowest leaf sheath reveals a dark shiny layer of fungal material on the stem that is easily scraped off. Weakened stems lean or lodge in various directions as in eyespot. In many instances, the disease is confined to the roots, and no symptoms appear on the crowns, stems and heads. The wheat take-all fungus produces spores (ascospores) inside tiny black structures (perithecia) on the sheath of the lower leaf and on stubble residues at the soil surface.

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Disease Cycle

The main source of the fungus is infested crop residues in the soil. The fungus survives best in the residues when the soil nitrogen content is high. Brown strands (hyphae) of the fungus grow from the residues, through the soil and over the surface of the roots, crowns and stems. The fungus spreads from plant to plant by means of "root bridges." Using a hand lens, it is often possible to see the brown strands on the roots while the roots remain whitish. The roots turn black after the fungus penetrates into them. Invaded crowns and stems develop a brownish, dry rot.

The severity of take-all generally increases as soil alkalinity increases (pH rises) and fertility (especially nitrogen and phosphorus) decreases. Wet soil, especially in spring and early summer, is highly favourable to the disease. Soil compaction aggravates take-all. Cool weather (12°C-18°C) is more favourable than warm weather. The disease is more severe when wheat is sown early than when sown near the end of September or in October. When wheat is grown continually on the same land, take-all becomes increasingly severe during the first 3-5 years, but subsequently declines. Take-all predisposes wheat to drought stress, especially in June and July.

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Management Strategies

Carefully manage soil fertility. Neutral to alkaline and infertile soils are most at risk. Do not apply lime before planting. Soils deficient in potassium and phosphorous cause plants to be more susceptible because of poor root development. Nitrate nitrogen increases disease severity. Control grasses and avoid early planting. Use a 3-year crop rotation and avoid planting wheat after wheat.

Updates on Cereals: Take-All

• Field Crop Protection Guide - Publication 812
  • Cereals: Wheat: Take-all

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Related links...

• Diseases
• Cereals

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