Take-All

Gaeumannomyces graminis

Biology

Take-all is primarily a disease of wheat but barley, oats, rye and a number of grass species can also be affected.

The fungus overwinters on infected crop residue. In spring, the fungus grows in the soil, comes into contact with the crop roots and causes infection. The fungus may grow from root to root infecting new plants. Infection may occur throughout the growing season, but the early infections are the most damaging because they move up into the plant crown. This disease organism is spread by transport of infested soil or crop residue from field to field.

Take-all is favored by cool soils (12-20 degrees Celsius) and high soil moisture. Alkaline soils, compacted, poorly drained soils, and nitrogen- and phosphorus-deficient soils increase disease severity. Elevated levels of take-all and plants with take-all like symptoms have been associated with copper deficient soils. The disease level may be greatly enhanced by some post-emergent foliar herbicide products. Cultivars such as Roblin and Oslo in particular can exhibit very high levels of take-all or take-all like damage if these herbicides are used on soils that are low or deficient in available copper.

Damage Description

Roots of infected plants are dark brown to shiny black and so rotted that plants can easily be pulled from the ground. Stems may also show this shiny black discoloration. Severely diseased plants are stunted with empty bleached white heads. These white heads stand out in patches in the crop.

Take-all is most severe after wheat is grown in the same field for two to four years. Light infestations may go unnoticed because affected plants show no symptoms, but under severe infestation levels, wheat losses of greater than 60 per cent have occurred.

The disease kills headed-out plants and in spring sown wheat, a 62 per cent infection of take-all reduced yields by 50 per cent. On spring sown barley a 64 per cent infection of take-all reduced yields by 24 per cent. This disease is progressive, spreading from plant to plant throughout the growing season.

Diagnosis

Diseased plants have bleached white heads that pull up easily and crowns and roots that are shiny charcoal black.

Management Strategy

• Rotate crop with non-host crops such as canola, flax or less affected cereal crops. Cereals in order of decreasing susceptibility are wheat, barley, triticale, rye and oats. Planting alfalfa, beans or soybeans in the rotation may not help reduce disease levels. Summer fallow reduces disease incidence in the following wheat crop.
• Maintain adequate nutrient levels, especially phosphorus and potassium. An application of lime on acid soils as well as an application of nitrate to winter wheat in the fall may increase disease severity.
• Control volunteer wheat and grassy weeds that may harbor the fungus.
• Deep till to bury stubble for faster decomposition.
• Do not transport infested soil or crop residue from field to field on equipment.
• Evaluate the effect of post-emergent herbicides. Check those areas in the field that may have missed being sprayed. Is there a difference in the levels of take-all?
• Check soil copper levels; any soil below 1 ppm copper could contribute to take-all severity. Ergot in grain, melanosis in wheat and pigtails in barley are indications of copper deficiency.