Disease biology

Leaf blotch

Summary

Scald attacks especially barley and rye. The worst attacks occur in winter barley. In case of severe attacks yield losses can amount to 15%. 1-2 cm long oval or irregular water-soaked spots appear on leaves and leaf sheaths. The colour later turns greyish-white (scalded) with a clearly purple or dark brown edge. The degree of attack is closely related to damp weather. In damp conditions scald is highly epidemic, and control should be carried out preventively if there is a risk of major attacks. The severest attacks are often seen on the lightest soils.

Mycology

The mycelium of the fungus is placed under the cuticula (the leaf surface). It forms a stroma with simple hyphae on which several transparent, 2-celled, 11-35 x 3-5 µm conidia are formed. The top cell is sickle-shaped. Systematics: Deuteromycotina, Hyphomycetes, Hyphomycetales, Dematiaceae.

Symptoms

1-2 cm long oval or irregular, water-soaked spots appear on leaves and leaf sheaths. Later, the colour turns whitish grey (scalded) with a distinctly purple or dark brown edge. The symptoms are often found on the leaf blade at the transition to the leaf sheath in the place in which water drops accumulate. The spots gradually merge into irregular areas. The leaf turns yellow around the spots, and the tissue dies. The attack is most pronounced on the lower leaves, but in case of severe attacks the fungus spreads to the top leaves and ears. In rye the leaf symptoms have a less distinct edge and are more lens-shaped. Can be mistaken for: Attacks in barley can sometimes be mistaken for scorching caused by herbicides.

Time of attack

In winter barley and especially at early sowing the first symptoms will show in October. The attacks are usually not visible until spring. In spring barley the symptoms will show from the elongation stage (stages 30-31) onwards in damp years.

Biology

The fungus lives on both volunteers and plant debris. The fungus is seed-borne to a lesser extent. Other hosts can sustain infectious matter. The survival period on plant debris is 6-12 months. The spores are spread through rain splash and to a lesser extent by the wind over short distances. Infection from one neighbouring field to another therefore only occurs to a lesser extent. Climatic requirements: The scald fungus thrives best under cool and humid conditions. The severest attacks are therefore found in winter barley. Spore formation and infection occur over a large temperature range with an optimum at 15-20°C – higher temperatures are inhibitory. For infection prolonged humidity is needed just as humidity is necessary for sporulation. The incubation period (the period from infection until symptoms are visible) is approx. 32 days at 10°C and at 18°C only 10 days.

Control measures

Prevention: Use a crop rotation with an interval between growing barley (both spring and winter barley) and use resistant cultivars even though most spring and winter barley cultivars are relatively susceptible to scald. Poor ploughing in of plant debris and volunteers increases the risk of attack; conversely, much infected plant debris only causes infection if the climatic conditions are favourable to the fungus. Forecast service: Aarhus University, Faculty of Agricultural Sciences and the Danish Agricultural Advisory Service issue forecasts. Keep up to date on the Internet under: Varsling/Registreringsnet (= Warning/registration network developed). Damage threshold: ongoing attacks are difficult to stop. Scald is highly epidemic under favourable climatic conditions. Control should be based on a risk assessment including the number of rainy days and cultivar susceptibility. Control is most relevant in winter and spring barley. Chemical control: It is difficult to control established attacks.

Names and distribution

English: Scald. Other names: Leaf blotch. Distribution: The fungus is widespread in all temperate areas on the globe.

Hosts and importance

Importance: In Denmark the major attacks occur in winter barley, next in spring barley and to a minor extent in rye. In cases of severe attacks the yield losses can reach 15%. The severest attacks often occur on the lightest soils. Hosts: Several grasses are attacked apart from barley and rye, among them couch-grass as well as rye-grass and brome species. Specialisation has been proved to the effect that scald in rye for instance cannot infect barley. However, in certain grass species infection of barley and rye can occur to a minor extent.

Names in different languages

Danish :	Skoldplet
German :	Rhynchosporium-Blattfleckenkrankheit
English :	Leaf blotch
Latin :	Rhynchosporium secalis
Norwegian :	Grå øyeflekk
Swedish :	Sköldfläcksjuka

Scald on barley

Scald

Late attack of scald in barley

Scald – new and old attacks

Septoria nodorum/Glume blotch attacks in barley can be mistaken for a scald attack

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