Disease biology

Ramularia leaf spot

Summary

In Denmark widespread attacks of Ramularia leaf spot were observed for the first time in 2002. Both spring and winter barley come under attack. The symptoms are dark brown spots surrounded by a yellow area. The spots are visible on both the top sides and undersides of the leaf. The spots follow the nerves. The need for control is determined on the basis of a risk assessment and depends on the susceptibility of the cultivar. At present, knowledge about which factors influence development of the epidemic is limited. Choosing highly resistant cultivars is at present the safest method of reducing attacks.

Mycology

The fungus produces tufts of swan’s neck-shaped conidiophores, which appear like pearls on a string through stomata on the underside of the leaf. The conidia are on average 8 µm long and 4.4 µm wide. The sexual stage of the fungus is not known. Systematics: Mycosphaerella (Ascomycetes).

Symptoms

Symptoms of attack show as dark brown spots surrounded by a yellowish area – especially at the ends of the dark brown spots. Attacks are visible on both the upper side and the underside of the leaf. The spots follow the leaf nerves. The first symptoms usually appear on the lower leaves from which the disease spreads to the upper leaves. The severest attacks occur on the second leaf from the top and the flag leaf. Can be mistaken for: The attacks of Ramularia leaf spot can easily be mistaken for spots caused by plant physiological factors. However, these are characterised by usually being found on the upper side of the leaves and by not having a yellow edge round the dark spots – there are no clear boundaries between the physiological spots. Ramularia leaf spot can also be mistaken for the spot type of net blotch and for mildew resistance necroses.

Time of attack

Winter barley can be infected as early as the autumn. In both winter and spring barley a significant development of the disease has so far only been seen after earing. The plant apparently needs to have reached a certain age before severe attacks develop.

Biology

The fungus produces many small spores that are easily spread by the wind. The fungus presumably overwinters on winter barley and volunteers. The epidemiology and population dynamics of the fungus are not fully known.

Control measures

Prevention: Keep the soil free from volunteers; this will reduce the risk of primary infection. Grow cultivars with low susceptibility – see the latest results from the Monitoring plots on Varsling/Registreringsnet (= Warning/registration network developed). Fungicide control has the best effect if it is carried out before or just about earing; the best results have been achieved by treatment between GS 37 and 51. The extra yields achieved through fungicide control have generally been rather limited.

Names and distribution

English: Ramularia leaf spot. Distribution: The fungus is found in Central Europe (Germany, Switzerland, Austria, the Czech Republic and Denmark) and in northern Europe (Ireland, Scotland and Norway). The fungus is also known from other parts of the world: Mexico, Uruguay, Argentina and the southern part of New Zealand.

Hosts and importance

Hosts: Spring and winter barley are the primary hosts, but the fungus has also been found on other cereals and grass species. Importance: Widespread attacks of Ramularia leaf spot were not established in Denmark until 2002. The fungus is now common; it was thus found on approx. 50% of the sites on which cultivar testing was carried out in 2003. There are reports from Germany, Switzerland and Austria of yield losses of up to 35%.

Names in different languages

Danish :	Ramularia bladplet
German :	Ramularia-Blattfleckenkrankheit
English :	Ramularia leaf spot
Latin :	Ramularia collo-cygni (Rcc)
Norwegian :	Spragleflekk

Ramularia leaf spot on barley, symptoms on leaves

Ramularia leaf spot and a larger Bipolaris net blotch in the middle of the leaf

Ramularia leaf spot – early attacks on barley

Ramularia leaf spot – late attacks on barley

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