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FRAG: Septoria Press Release 0104

logo: frag Press Release 01/04

FRAG-UK: Guidelines for Septoria tritici resistance management in cereals for 2004

2003 saw the widespread occurrence of strains of Septoria tritici resistant to strobilurin fungicides (QoIs). Fortunately, where resistance management advice was followed disease control was still effective but only when mixed with a high rate of a DMI fungicide.

Strategic planning

Fungicide programmes should be designed primarily to ensure good disease control and to protect the activity of the fungicides for the future. The following principles should help to achieve both objectives.

Mixtures

For Septoria tritici, and many other cereal diseases, fungicide mixtures are the key to reliable disease control and yield protection. It is vitally important that mixtures should include partner fungicides with a different mode of action and be used at doses that are high enough to give effective control of the target disease. For control of Septoria tritici, any mixture should be based around a triazole (DMI) products. Strobilurins, when added to a triazole can broaden the disease control spectrum, maximise green leaf retention and yield. Each mixture partner can also help insure against resistance in the target pathogens.

Exposure time

The longer pathogen populations are exposed to a fungicide the more likely it is that resistance will develop. Using fungicides only where appropriate, and as a part of a broader Integrated Pest Management strategy, will help reduce resistance development. Always avoid multiple low-dose sequential applications of fungicides from the same group.

Dose

Using high doses (particularly of fungicide mixtures) gives more robust disease control, protects against yield loss due to disease and may help to prevent further resistance development. Effective disease control is likely to restrict spread of resistant populations. It is important to follow manufacturers’ recommendations.

Timing

Timing of the sprays should be based primarily on disease pressure and local experience. If possible, treat crops before the disease becomes well established. However, where curative action is required only use products with a label recommendation for curative action. Further advice on timing is contained in the HGCA publication Wheat disease management guidelines (http://www.hgca.com).

Guidelines on the use of individual fungicide groups

The following guidelines will help to preserve the effectiveness of fungicides. For active substances not listed below see the product label or guidance on cereal fungicides available on the FRAG-UK website at Fungicide Resistance Action Group (FRAG).

QoIs (strobilurins)

  • Never apply more than two foliar applications of strobilurin fungicides to a cereal crop (this has been a legal requirement since the 2003 season).
  • Always use strobilurins in mixture with a robust dose of a DMI effective against septoria. The addition of chlorothalonil to the two-way mixture is particularly effective at the stem extension to first node and at flag leaf emergence growth stages.
  • Where possible, use strobilurins as protectant fungicides and not when disease is well established.
  • Use robust doses of strobilurins to ensure good disease control and optimise yield benefits.

DMIs (triazoles and imidazoles)

Shifts in sensitivity have been detected to this chemistry, so it is important not to compromise performance by inappropriate use.

  • Repeated applications of DMI fungicides alone should not be used on the same crop in one season, as this will compromise the anti-resistance strategy.
  • Use DMIs in mixture with fungicides of a different mode of action. The mixture partner should offer reliable control of the target disease, i.e. chlorothalonil or dithiocarbamates.
  • The use of low doses of DMIs should be avoided, as there is evidence that they are ineffective. Apply at a dose that would give disease control if used alone.

Phthalonitrile (chlorothalonil)

  • Apply preventatively, alone before stem extension, or later in partnership with DMIs, or as an additional partner in strobilurin and DMI mixtures.

Dithiocarbamates

  • Apply preventatively in mixture with DMIs or as an additional partner in a strobilurin and DMI mixture.

If you are unsure about any of the suggested actions, or want them interpreted for your local conditions, consult a professional BASIS qualified agronomist.

For further information relating to fungicide resistance contact Dr Judith Turner, Chairman FRAG-UK, The Food and Environment Research Agency, Sand Hutton, York, YO41 1LZ , UK. Tel: +44 (0)1904 462200, Fax: +44 (0)1904 46211.

Notes for Editors
  1. FRAG-UK was established in 1995 to, amongst other things, gather and interpret information on fungicide resistance and its management and to arrive at a UK consensus view.
  2. FRAG-UK provides an interface between industry's Fungicide Resistance Action Committee (FRAC) and independent research organisations.
  3. Fungicide resistance is a major area of concern to the agrochemical industry. Millions of pounds are spent in developing new compounds and obtaining registration for use from the authorities. This investment can be lost when plant pathogens become resistant to fungicides. Any loss of a previously effective fungicide may mean that there is a gap in the armoury available to control the devastating effects of disease on yield and quality.
  4. FRAG-UK promotes practical guidance on the status and management of fungicide resistance in the UK. It indicates areas where research and development are required and produces, publishes and promotes educational material that will assist in the understanding of, and reduce the incidence of, resistance in plant pathogens (FRAG-UK's Web-site can be found at Home Page)
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