Integrating disease management for barley
For effective disease management, it is important to use a combination of practices that focus on the factors affecting disease (Table 1). Over-reliance on any one factor to control common foliar diseases, such as fungicide alone, will not be as effective or sustainable as an integrated management approach.
Variety choice and implications for disease management
Grain quality and agronomic adaptation often determine the choice of variety. Knowing the responses of your variety to disease (for example, resistance or susceptibility) will help to determine the need for other disease management approaches. Resistance profiles of barley varieties grown in WA vary across the spectrum of diseases. Current malting varieties are generally more susceptible than feed varieties. See the annual Crop Sowing Guide for Western Australia for information on the response of current varieties to foliar disease.
|Disease||Cultivar resistance||Crop rotation||Stubble destruction||Disease-free seed||Chemical# seed||Chemical# foliar|
|Scald||1 to 3||1||1||2||2||1|
|Spot-type net blotch||1 to 3||2||1||3||1||2|
|Net-type net blotch||1 to 3||2||1||2||1*||2|
|Powdery mildew||1 to 3||3||3||3||2||1|
|Barley leaf rust||1 to 3||3||3||3||2**||1|
|Barley yellow dwarf virus||1 to 2||3||3||3||2||2|
Key: 1 = very effective, 2 = moderately effective, 3 = not effective
# Fungicide use is indicated except for barley yellow dwarf virus for which insecticide use is indicated.
* Several seed dressings are registered to control seed-borne net-type net blotch.
** No fungicide registered at the time of publication.
Fungicide disease management
Fungicide at seeding
Fungicide seed dressings or fungicides applied in-furrow with fertiliser can be useful in disease protection or suppression of early seedling infection. The recently released seed dressing fungicide Systiva® (fluxapyroxad) is registered for the control of both STNB and NTNB. It provides systemic protection and may reduce the need for a first foliar fungicide at tillering to stem extension. The length of protection provided by this fungicide and any yield response will be dependent on inoculum load, variety susceptibility and seasonal conditions. The choice of fungicide should be determined by the target diseases, fungicide resistance status and information on seed dressing and in-furrow fungicides for cereals in WA.
The aim of foliar fungicide application in the crop is to delay disease development and to maintain green leaf area which reduces disease impact on yield and grain quality. In barley, the most important contributors to yield are leaf two (flag-1), leaf three (flag-2), the ear and upper stem, while the flag leaf is relatively unimportant. Protecting leaf two and leaf three is the highest priority in effective disease control.
The cost effectiveness of foliar fungicide applications depends on disease severity, susceptibility of the variety, yield potential of the crop, grain quality outlook and the environment where the crop is growing.
Reliance on fungicide is much greater in medium to high rainfall areas than in low rainfall regions due to higher disease pressure and longer growing seasons during which the disease epidemic may increase. For instance, in the medium rainfall region a single application of fungicide may be required at late stem elongation to flag leaf emergence stage (Z33-39). In a long season, high rainfall area two fungicide sprays are often required: one at early stem elongation and a follow-up spray at or just prior to flag leaf emergence. When susceptible varieties are grown in conditions favourable for disease development, such as disease prone areas or high rainfall seasons, fungicide can be cost effective in reducing the disease impact where yield potential is over 2.0t/ha. Under high disease pressure, using higher fungicide rates will give longer residual protection. The choice of fungicide should be determined by the target diseases, fungicide resistance status and information on registered foliar fungicides for cereals in WA.
Rotation and stubble management
Diseases such as scald, spot-type net blotch and net-type net blotch are stubble borne. Paddock selection is important to minimise stubble-borne diseases. Crop rotation with a non-host crop in the previous year will minimise initial inoculum levels for the current season's crop. To further reduce disease pressure, avoid sowing the current season's crop in paddocks adjoining those with barley stubble from the previous season. Cultural practices such as incorporating the residue into the soil or removing it completely (for example, by burning) will reduce the abundance of the pathogen and the disease pressure. Stubble may be reduced by baling and grazing; however, these methods only result in a small reduction in the disease pressure. Stubble reduction must be balanced against the increased risk of soil erosion by wind or water.
Green bridge management
Three major diseases, barley leaf rust, powdery mildew and barley yellow dwarf virus (BYDV), persist on living hosts. Barley leaf rust survives on barley volunteers, powdery mildew on barley volunteers and stubble, and BYDV on cereal regrowth and perennial grasses. A green bridge of self-sown barley leading into the cropping season provides host material for these diseases and the aphid vector of BYDV and increases the risk of their early onset. Removing this green bridge as early as practicable before seeding will greatly reduce the risk of early crop infection. Further information is available on control of green bridge for pest and disease managment.
The foliar diseases scald and net type net blotch and the head diseases loose smut and covered smut can be seed-borne. Sowing infected seed can introduce disease into a new crop. Therefore clean seed should be used wherever possible. Fungicide seed dressings can reduce the risk associated with sowing infected seed, particularly for smuts and bunts. See seed dressing and in-furrow fungicides for cereals in WA for further information.
In addition, barley yellow dwarf virus (BYDV) is a threat in aphid prone areas.
Other causes of leaf spotting in barley
It is important to remember that abiotic factors such as nutrient deficiencies or adverse weather conditions can also cause abnormalities in barley leaves. Some barley genotypes exhibit varying degrees of physiological spotting on leaves which can also be confused with disease symptoms.
An important starting point in disease management is correct identification as diseases differ in their best management strategies. See specific disease pages on this site for symptoms and effects. Further assistance with disease identification can be obtained from DDLS - Plant pathology services.