Biology and impact

Take-all is a serious root disease of wheat crops which is found worldwide. It is caused by the soil dwelling ascomycete fungus Gaeumannomyces graminis var. tritici. The fungus is also able to infect the cereals barley, triticale and rye, as well as a number of common grass weed species such as couch grass and the bromes. Another variety of take-all fungus (Gg var. avenae) is able to infect oats and other cereals but this is currently very rare in the UK. The disease develops in short wheat rotations where wheat or other susceptible cereal species are grown consecutively for two or more years in the same field. Second wheat crops in the rotation will typically yield around 10-15% less than a first wheat crop, primarily due to take-all. In notable outbreak years, where weather conditions are particularly conducive to take-all development (e.g. 2008, 2009 and 2012), yield losses of up to 60% have been reported and grain quality will also be greatly reduced. In the 2015/2016 season, the weather conditions were conducive for the take-all fungus and readily observable disease symptoms appeared from mid-June onwards in some cropping situations.

In the first wheat crop in a rotation, take-all fungal inoculum builds-up in the soil root-zone or rhizosphere but there is generally very little root infection or minimal risk to the crop’s performance. However, if a second wheat crop is then sown on the same site there is a risk of severe take-all disease developing. The fungus invades the root tissue causing black necrotic lesions which restrict the uptake of water and nutrients from the soil. In severe disease outbreaks, characteristic patches of stunted, prematurely ripening plants will develop after flowering and during grain filling. In between cropping seasons, the fungus survives on root debris from the previous crop.

Take-all fungal inoculum build-up in 1st wheat crops and disease development in subsequent crops are both favoured by wet conditions in the spring and early summer. Take-all patch development during grain filling and yield losses can then be exacerbated by high evapotranspiration caused by dry, hot and/or windy weather during grain filling. Patches, 1m to 5m in diameter, first appear from mid-June onwards and are randomly present across a wheat or barley field.

Management Options

  • Plan well in advance before drilling a 2nd cereal crop.
  • Crop rotation with non-cereal broad-leaved break crops or oats (provided that the oat attacking strain of the take-all fungus is not present) will control take-all disease in a following 1st cereal crop.
  • Ensure there is good control of cereal volunteers and grass weeds (particularly couch grass and bromes) through the break crop. If present these plants can carry over significant amounts of take-all into the subsequent 1st cereal crop.
  • After harvest of the first wheat crop take-all inoculum begins to decrease in the soil. A longer inter-crop period by later sowing (preferably mid-October or later) of second and subsequent wheat crops can therefore help to reduce disease severity. It is important that cereal volunteers are well controlled during this inter-crop period.
  • Maintaining phosphate and potassium above index 2 can help to reduce disease severity. Ideally any nutrient deficiencies should be corrected before the break crop and sequence of wheat crops begins.
  • In crops at risk of take-all disease (non-first wheats) a split nitrogen application with an early application in Feb or March before the main application in April can help reduce the impact of take-all.
  • Seed treatment fungicides: silthiofam (commercially available as Latitude) can provide partial control against take-all but should be combined with other control strategies. NB. Fluquinconazole, which was previously available as Jockey, is no longer available.
  • Foliar fungicides: azoxystrobin (Amistar) applied during stem extension can help to control take-all. Performance can be quite inconsistent under field conditions.
  • No resistance against take-all is available in AHDB Recommended List varieties. However, first and second wheat yield performance are provided on the RL and can give indications as to those varieties which yield best as a second wheat in the rotation.
  • Growing alternative cereal species rather than wheat can reduce the risk of damaging take-all. Barley is very susceptible to take-all but generally suffers lower yield losses. Triticale shows moderate resistance to disease. Rye is highly resistant and will re-root when take-all infections have occurred. None of these species act as an effective break crop and they are all capable of building up potentially damaging amounts of take-all fungal inoculum in the soil. However, barley, triticale or rye can be grown instead of wheat in ‘at risk’ rotational positions (i.e. to replace the second or third wheat in the rotation).
  • Continuous wheat cropping can be practised (if black-grass isn’t a problem) to take advantage of the phenomenon of take-all decline (TAD). This natural decline in take-all disease and yield improvement usually occurs from the 4th or 5th wheat crop onwards due to natural build-up of useful antagonists. Unfortunately, a severe take-all outbreak during the second to fourth wheat crops is required to trigger the onset of take-all decline.