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Take-all Disease in Cereal Crops

Take-all disease in cereals is a cause of major concern for farmers due to its widespread distribution and the absence of any varietal resistance or any effective chemical control. It is estimated that efficient control of the disease could increase yields by 10-50% in affected crops.

The disease is important, however, not merely because it reduces yields but also because it can restrict both cropping and sowing date options.

Effects of the disease are likely to be worsened if nitrogen is restricted. Additionally, root loss caused by Take-all has the potential of increasing the risk of nitrate leaching. For such a serious disease and its potentially damaging consequences it is important to understand the factors which contribute most to its occurrence and impact on cereal production.

Symptoms:

The first visual evidence of Take-all is usually the occurrence, from Growth Stage (GS) 31 onwards, of patches of stunted plants in the crop with pronounced leaf yellowing and the possible reduction in secondary tiller development. Heads ripen prematurely and are bleached white and sterile.  Above ground symptoms can be very similar to drought.

Examination of affected plants for blackening of some roots will confirm Take-all as the problem. Plants may break free at the crown when pulled from soil. If dry conditions persist during the grain fill period significant losses can still occur even in the absence of obvious patches or Whitehead symptoms.

Take-all is favored by alkaline, compacted, infertile (esp. nitrogen and phosphorus-deficient) and poorly drained soils. Rotation may reduce disease incidence in fields where Take-all has been a problem.

Sources:

Volunteer cereals and grass weeds act as major sources of inoculum for carry-over of the disease to subsequent crops. Perennial grass weeds such as couch play an important role in carrying infection through non-susceptible break crops, and by competing for nitrogen and other nutrients can increase the crop's susceptibility to Take-all. The presence of volunteer cereals or grass weeds will reduce set-aside effectiveness as a break crop from Take-all. Infected Stubble, especially in successive cereal cropping situations, is another source of inoculum build-up.

It is thought that the pathogen can survive in the soil for over three years and survival time increases as the soil pH decreases.

Spread:

Germinating seedlings from a newly planted cereal crop come into contact with the Take-all pathogen, through any one of the sources above. Colonisation of roots continues to occur as the season progresses, with infection active at temperatures in the 2-25C range. Root infections lead to restrictions in nutrient uptake and eventual losses in crop yield and quality.

Management practices:

  • Avoid continuous cereal cropping practices.  Wheat grown after a break crop usually does not get much take-all.
  • Avoid early sowing of cereal crops. If sown early seed treatments can help, especially if used in combination with cultural control.
  • Avoid loose seedbed conditions.
  • Reduce seeding rates, to avoid dense cropping.
  • Correct any drainage or soil structure problems.
  • Avoid high nitrogen applications.  Where take-all is likely to be a problem apply the nitrogen early.
  • Ensure high grassweed control in previous crops.
  • Eliminate couch prior to planting.
  • Some varieties can suffer less yield loss for a given level of take-all.  Those with some tolerance include Napier, Savannah, Option and Consort.

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