Disease biology

Ear blight / Scab

Summary

Fusariosis, which comprises seedling blight, brown foot rot and ear blight, attacks all cereals. Several Fusarium species are included in this complex. Roots, straw, leaves as well as ears are attacked. The symptoms show as failing germination and discolouring of the leaves, leaf sheaths and straws. Attacks on ears show as incompletely ripe small ears.

Mycology

Mycology: There are many Fusarium species. Typically, all conidia are sickle-shaped (curved) with 1-7 partitions. The ascospores are transparent. The perithecia measure 120-250 µm. Systematics: Ascomycotina, Pyrenomycetes, Sphaeriales, Hypocreaceae.

Symptoms

Various plant parts can be attacked, and various Fusarium species can be involved. Seedling blight shows as failing or incomplete germination in large or small patches in the field. The shoots can be curved, spiral or partly wilted. The growth of germinated plants is inhibited. The base of the shoot or the roots can also be dark. Brown foot rot results in fairly large, diffuse discolourations or streak-shaped lesions on the leaf sheaths. Later on, they can also be found at the base of the straws. The symptoms vary a lot; at times, the entire base of the straw is reddish brown with a tendency to formation of streaks or only the lower part of the straw is discoloured. There can also be a reddish tinge of fungus spores. The growth of plants with severe attacks of brown foot rot is inhibited, the plants tiller less, and the ears ripen incompletely. Fusarium on leaves is most widespread on the lower parts of the plant. Early leaf symptoms appear at the base of the first and second leaf with reddish brown, oval, slightly sunken lesions surrounded by a dark brown edge. Ear attacks appear after flowering as totally or partly incompletely ripe ears. In damp weather a reddish coating of spores is visible. The grains shrink and the viability is reduced. Can be mistaken for: Brown foot rot can be mistaken for other fungi that cause discolouration of the base of the straw: eyespot, sharp eyespot or snow rot. Ear attacks by Fusarium are easily recognisable, especially when the reddish spore slime becomes visible.

Time of attack

Attacks can occur during the entire growing season.

Biology

The Fusarium fungi live on plant debris and they can also be seed-borne. The spores are only spread by wind and rain splash over rather short distances. The fungus spreads from the lower parts of the plant and produces many spores on dying leaves from which the ear is infected. The ear can also be infected as a result of infection by wind. Climatic requirements: The various Fusarium species have different climatic requirements. F. culmorum and F. graminearum cause especially seedling blight at high temperatures and when the soil is dry. Brown foot rot is also promoted by high temperatures and dry conditions; therefore symptoms do not show until relatively late and most clearly at a late harvest. Attacks of the ear are promoted by precipitation during flowering and high temperatures.

Control measures

Prevention:
Use healthy or fungicide-treated seed. If more than 30% of the grains are infected, treatment is recommended. A healthy crop rotation is important as the fungus survives for a considerable time on plant debris. Good germination and growing conditions reduce the risk of seedling blight. Short-strawed cultivars are generally attacked in the ear because the spores are more easily spread to the ear. The Danish Plant Directorate carries out analyses of fungicide treatment needs against fusariosis.

Control:
Several approved fungicides against seed-borne infection with Fusarium are approved. At present there are no approved fungicides against brown foot rot and ear blight. Control of ear blight should be carried out at the time of full flowering (stage 65). However, in practice it is difficult to achieve a high control effect on ear blight.

Control guidelines for Fusarium in winter wheat
Chemical control can be appropriate at growth stages 61-65 if:
- the precrop is Wheat, Maize or Triticale
- the cultivation method is reduced tillage
- cultivars other than Skalmeje – the most resistant cultivar – are grown
- it has been raining – or it is likely to rain – during wheat flowering

In order to achieve an effect against ear blight, it can be a good idea to postpone the final treatment until during flowering. This treatment is typically the second application in a split ear treatment. The following 3 products have – in the doses stated – an effect on ear blight:
- 0.5 l/ha Folicur
- 0.5 l/ha Juventus
- 0.4 l/ha Proline (Proline also has the best effect on tan spot and Septoria)

Names and distribution

English: Fusariosis. Depending on the symptom the diseases are called seedling blight, brown foot rot or Fusarium foot rot and ear blight. Distribution: Fusarium is widespread in areas with a large production of cereals. Which Fusarium species are most widespread vary from area to area, but F. culmorum and F. avenaceum seem to be more widespread in Denmark.

Hosts and importance

Importance: There are no Danish surveys of the importance of Fusariosis attacks. Losses from brown foot rot in stressed crop rotations are in other countries assessed to be up to 50%. Losses of 10% are more common, but often there are at the same time other diseases on the base of the straws, which makes it difficult to distinguish between the losses caused by the individual diseases. According to non-Danish surveys ear blight can cause yield losses of 10% and lower the quality of the grain as a result of a possible formation of toxin. Hosts: The Fusarium species mentioned have many hosts. All four cereals can be attacked but especially winter wheat and rye. Several grasses can also be attacked. One Fusarium species can differ to a great extent concerning both its way of attack and its appearance on different hosts, depending on its origin.

Names in different languages

Danish :	Fusarium
German :	Fusskrankheit / Ährenskimmel
English :	Ear blight / Scab
Latin :	Fusarium avenaceum
Norwegian :	Fusariose
Swedish :	Fusarios

Attack by ear blight in wheat with wholly or partly incompletely ripe ears

Ear blight in wheat under normal field conditions

Ear blight in wheat. At high air humidity the attack will result in vigorous mycelium growth

Early Fusarium attack

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