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Causes of Barley Diseases

Barley Home

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(Adapted from Cereal leaf and stem diseases, Grains Research and Development Corporation, 1992, edited by Hugh Wallwork)

| Barley Diseases | Chemical Control | Effectiveness of Management | Integrated Disease Management |

In barley, disease causing organisms (pathogens) often reduce grain yield by damaging green leaves preventing the production of sugars and proteins needed for growth. They can also block or damage the plants internal transport mechanisms, reducing the movement of water and sugars through the plant. Yields are also reduced when the pathogen diverts the plants energy into producing more of the pathogen at the expense of plant growth or grain formation.

The main pathogens that cause disease in barley are fungi, although viruses and nematodes can also damage crops in Western Australia.

Fungi

Fungi come in a wide variety of forms. They spread by producing one or more types of spores, which may be carried by wind, through rain-drop splash or in the case of smuts, by seed.

Many fungi survive inside plant residues and produce fresh spores in the following season. Some survive as spores in the soil or on seedRust requires continuous green host plants to colonise so that they can survive from one season to the next.

Viruses

Viruses are invisible to the eye and even through a conventional microscope. Unlike other pathogens, viruses are totally dependent on the host plant for growth and multiplication. They cannot survive outside the plant except when in an insect or other animal that transmits the disease. Aphids for example transmit barley yellow dwarf virus. Viruses damage plants by blocking their transport mechanisms.

Nematodes

Nematodes are elongate, tubular roundworms that cause a variety of diseases. They are microscopic in size and are identified only with the aid of a microscope. Nematodes feeding on plants can cause direct damage by reducing the root area or damaging their transport mechanism. In addition, nematode feeding predisposes the plant to attacking by other pathogens.

Barley Diseases

The development of diseases in barley depends upon

  1. Presence and abundance of the pathogen (disease causing organism).

    2. The initial amount of a pathogen that is present is affected by a range of management factors including paddock rotation, stubble retention and the presence of a green-bridge. The amount of disease present in the previous barley crop is also a factor.

  2. Resistance of the variety to a disease.

    A pathogen will induce more disease when the variety that is being grown is susceptible. Complete resistance, while sometimes possible, is rare. For this reason combining varietal resistance with other management options is valuable. In the absence of varietal resistance, a fungicide may sometimes be used to reduce the risk of disease.

    Complete resistance, while sometimes possible, is rare. For this reason combining varietal resistance with other management options is valuable. In the absence of varietal resistance, a fungicide may sometimes be used to reduce the risk of disease.

  3. Suitable environmental conditions.

    Pathogens are more active at certain times of the year as they respond to temperature and moisture conditions that are suitable for their infection and reproduction.
    Conditions of high rainfall and mild temperatures favour the development of many diseases. Such conditions can vary with regional location as well as sowing date.

    Conditions of high rainfall and mild temperatures favour the development of many diseases. Such conditions can vary with regional location as well as sowing date.

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Chemical Control

Table 1: Effectiveness of Management on Barley Disease Control

Diseases

Cultivar Resistance

Crop Rotation

Stubble Destruction

Disease Free Seed

Chemical

Seed

Foliar

Scald

1-2*

1

1

2

2

1

Net-type net blotch

1-2*

2

1

3

3

1

Spot-type net blotch

1-2*

2

1

3

3

1

Powdery mildew

1-2*

3

3

3

2

1

Leaf rust

1-2*

3

3

3

2

1

Barley yellow dwarf virus

1-2*

3

3

3

2**

1**

Covered smut

-

3

3

1

1

3

Loose smut

-

3

3

1

1

3

Chemical Control

The choice of fungicide should be based on the spectrum of diseases present in the crop. New fungicides are regularly registered for the treatment of various foliar diseases in barley. Refer to the current Western Australia Department of Agriculture Cereal Foliar Fungicide Chart for the most up to date registrations.

Integrated Disease Management

For effective disease management, combine practices that focus on the different factors affecting disease. Over reliance on any one factor - the "silver bullet" approach - will not be as effective or sustainable as an integrated management approach.

See Table 1: Effectiveness of Management on Barley Disease Control

Crop Rotation

Crop rotation is very effective for stubble-borne diseases. Do not plant consecutive barley crops in the same paddock. In high rainfall/high disease risk areas a four-year rotation is preferred.

Stubble Management

Tillage practices that incorporate the crop residue into the soil aiding its breakdown or the burning of stubble will reduce the abundance of fungal pathogens that are carried over on the stubble such as scald, net-type net blotch and spot-type net blotch. Such practices must be balanced against the increased potential for soil erosion by wind.

Choice of Variety

Grain quality and adaptation to the region often determine the choice of a barley variety. Knowing your varieties' response to disease is important for determining the need for implementing other disease management strategies.

Fungicides

Fungicides can be effective in reducing the impact of disease when applied to susceptible varieties that are grown in disease prone areas or high rainfall regions. The availability of low cost fungicides and the more reliable production of malting quality grain with expected yields over 2.5 t/ha provide increased opportunity to profit from fungicide disease control.

Page amended : June 2007