Disease biology

Eyespot

Summary

Eyespot attacks winter cereals, especially wheat and rye in which losses of 10-15% can occur, whereas there is less damage in winter barley. Eyespot shows 6-8 weeks after the plant has been infected – from growth stage 26 – by irregular water-soaked spots or discolourations appearing uttermost on the leaf sheath just above the soil surface. The typical, oval, lightbrown-greyish spots at the base of the straw that resemble eyespots surrounded by a dark edge cannot be seen until stage 75. The transport of water and nutrients is inhibited. Lodging can occur in case of major attacks. Eyespot can be prevented through crop rotation.

Mycology

The eyespot fungus produces 2 kinds of mycelia: a yellowish brown linear or branchy one and a dark one. The dark is stromalike and the cause of the dark, superficial spot on the stem. The conidia are transparent, slightly curved and often with 5-7 cells. The size of the conidia is 1.5-3.5 x 35-70 µm. Systematics: Deuteromycotina, Hyphomycetes, Hyphomycetales, Moniliaceae.

Symptoms

Eyespot is visible 6-8 weeks after infection, from growth stage 26, when irregular water-soaked spots or discolourations appear on the edge of the leaf sheath just above the soil surface; these can spread into the leaf sheath. Later on, dark brown, point-shaped mycelium accumulations (stroma) are formed in the attacked tissue. The leaf sheaths are torn open in several places in the attacked tissue. Healthy plants are white as leeks at the basis. The typical oval, light brown or greyish spots, at the base of the straw, that look like eye spots surrounded by a dark edge are not visible until stage 75. When the leaf sheaths are removed, black dots can be seen in some cases (stroma tissue). Because the water and nutrient transport from the roots is inhibited, the plants ripen incompletely and the grains shrivel. Severe attacks can result in lodging. The symptoms in the spring are more easily recognisable in WHEAT than in RYE. The summer symptoms in rye resemble those of wheat but often include more of the stem and are diffuse. In WINTER BARLEY a reddish brown discolouration along the leaf sheath (rusty) or well-defined discolouration on the leaf sheath is visible. If the leaf sheaths are removed, small dots are often visible, and the stem beneath has a yellow tinge. The stems are often evenly discoloured all over. The eyespots show as a uniform brown colouring, often with a light middle. Can be mistaken for: The symptoms can in the spring be mistaken for attacks by Fusarium, sharp eyespot or snow rot.

Time of attack

Even though the infection takes place both in the autumn and in the spring, the symptoms usually do not show until spring. Infection can occur during the entire growing period, but the early attacks result in the heaviest losses.

Biology

Eyespot survives on infected plant debris. The period of survival is approx. 2-3½ years on clay soil and 1-2½ years on sandy soil. During the autumn, winter and spring months the fungus sporulates from the straw and is spread via rain splash and wind over short distances to the germinating plants. Climatic requirements: Temperatures between 4°C and 13°C and a relative air humidity of more than 80% lasting at least 15 hours are together with precipitation necessary for effective infection. The growth of the fungus in the plant increases until approx. 20°C. Humid and cool weather in the autumn, mild winters and a cold and humid spring favour fungal infection and growth possibilities in the plant. A dry spell in May-June inhibits the attack. The incubation period (the period from infection until the symptoms are visible) is approx. 30-55 days depending on the temperature.

Control measures

Prevention: Avoid crop rotation with a large amount of winter crops and plough in infected plant debris. There is not a lot of difference in cultivar resistance, but short- and stiff-strawed cultivars suffer less damage. Too early sowing of rye and wheat, especially second-year wheat, should be avoided. A dense plant population, such as can be seen after peas and horse beans, promotes eyespot attacks. Control of eyespot, if any, should be carried out in the spring because this is the time at which the extent of the attack can be assessed. See the guiding control threshold here: Dyrkningsvejledning.

Names and distribution

English: Eyespot. Distribution: The fungus has been found in almost all cereal producing countries.

Hosts and importance

Importance: The force of the attack depends on the climatic conditions, infection pressure, growing conditions and the crop rotation in particular. Yield losses of 10-15% can occur; exceptionally, up to 30% in cases of major attacks. Attacks in rye and wheat cause the highest losses while winter barley is good at compensating for the attacks. Hosts: All cereals and a few wild and cultivated grasses can be attacked. Among the cereals the winter crops in particular come under attack. The spring crops are attacked when there are possibilities of infection in the spring, but the attacks are rarely of importance. Among the grasses for instance couch-grass, loose silky-bent, wild-oats, perennial ryegrass and timothy are attacked, but these hosts are considered to be of no importance for the spreading of the fungus.

Names in different languages

Danish :	Knækkefodsyge
German :	Halmbruchkrankheit
English :	Eyespot
Latin :	Pseudocercosporella herpotrichoides
Norwegian :	Stråknekker
Swedish :	Stråknäckare

Left: a healthy wheat plant; right: plants attacked by eyespot

Minor eyespot attacks

Fusarium attacks which here can be mistaken for eyespot

Attacks of sharp eyespot can be mistaken for eyespot

Sharp eyespot is found higher up on the straw than eyespot

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