Disease biology

Take-all

Summary

The severest attacks are on wheat, then rye and winter barley. In case of major attacks yield losses of 30% or more are seen. Attacks are severest on light soils. Attacks show in late summer as patches of incompletely ripe plants because the roots die. The dead roots are black. The plant population is thin, the growth low and the ears are white and erect. The take-all fungus is a typical crop rotational disease. A crop rotation with just one non-susceptible crop reduces the infection significantly. Today, it is also possible to use seed treated with a fungicide that inhibits take-all.

Mycology

Longitudinal hyphae (4-7 µm in diameter) are formed in the soil; they send out a cushion (9-15 µm), which fastens on the roots and attack these. Perithecia are only formed under damp conditions at the time of ripening. The perithecia break through the leaf sheaths. They are black and measure 0.2-0.4 mm in diameter. Asci (10-15 x 80-130 µm) with 8 ascospores in each are formed in the perithecium. The ascospores measure 3-4 x 70-100 µm and have 3-7 partitions. They have a distinct ring at the top, 2-3 µm in diameter. Systematics: Ascomycotina, Pyrenomycetes, Sphaeriales, Diaporthaceae.

Symptoms

Patches of incompletely ripe plants can be seen in late summer in some areas of the field. The plant population is thin, the growth low, and the ears are erect. White ears are formed. Secondarily, attacks by black mould fungi occur in the ear. At first, only a few plants ripen incompletely. Infection can occur as early as the autumn when attacked plants have limp or light blades. At first, small, dark brown lesions are visible on the roots and root collar of incompletely ripe plants. Gradually, the entire root turns black. The attack can spread from the root collar to the basis of the straw. Because of the attack the plants tries to form new roots. In case of severe attacks it is easy to pull up the plant. Water and nutrient transport is inhibited by the black coating on the roots resulting in incompletely ripe plants. Can be mistaken for: At a distance the symptoms can be mistaken for damage caused by drought.

Time of attack

Infection can occur as early as the autumn, but symptoms on the above-ground parts usually do not show until June-July when new root growth stops.

Biology

The take-all fungus is a typical crop rotational disease, which survives in the soil on attacked root and stubble debris. The fungus can survive in the soil for 1-2 years. The mycelium grows into the young plant roots and destroys them. Infection occurs throughout the entire growing season. The infection is only spread over short distances through transport of infected plant material. Climatic requirements: The influence of take-all is increased by a hot and humid autumn, a mild and rainy winter with a wet early summer followed by drought from late June and July onwards.

Control measures

Natural enemies: The soil contains a number of microorganisms with an inhibitory effect on the fungus (antagonists). In case of continuous growing of a susceptible crop a so-called ”decline effect” will set in after a few years at which the degree of attack will decrease due to propagation of antagonists. Prevention: Crop rotation is the most important preventive measure; growing a non-susceptible crop for a year will reduce the risk of infection considerably. Rapid decomposition of root and stubble debris reduces the risk of survival. Removal of straw does not have a major influence because the infectious matter is mainly found on the roots. There is no resistance which means that differences between cultivars are caused by the ability of the cultivars to compensate with new roots. Early sowing increases the risk of attack, and therefore second-year wheat should be sown last, also because of the risk of eyespot attacks. Application of extra nitrogen and favourable growing conditions for the plants in general reduce the damage caused by the attack. Chemical control: Nowadays, it is possible to use seed that has been treated with fungicides that inhibit and delay the development of take-all. Fungicide treatment is only recommended for second-year wheat fields.

Names and distribution

English: Take-all. Distribution: The fungus is widespread all over the world but is found mainly in temperate climates and on rather poor soil.

Hosts and importance

Because the force of the attacks depends very much on cultivation area and cultivation technique, the importance of the fungus varies. Attacks are most severe on lighter soils. Yield losses of 30% or more can occur in stressed crop rotations. Non-Danish studies have shown that for every 2% of attacked plants the yield is reduced by 0.6%. The yield losses are mainly caused by fewer earlets and shrivelled grains. A rye field moderately attacked can involve a high risk of infection for a subsequent wheat field. Severe attacks can occur in winter barley, but the damage is rarely very large due to early ripening. Wheat growing after winter barley is very risky and is not recommended when there is a risk of take-all. Hosts: Take-all attacks wheat most severely, then triticale, rye and winter barley. Oats are not attacked by the fungus types found in Denmark. Several grass species, for instance couch-grass and maize, can also to a lesser extent act as hosts.

Names in different languages

Danish :	Goldfodsyge
German :	Schwarzbeinigkeit
English :	Take-all
Latin :	Gaeumannomyces graminis
Norwegian :	Rotdreper
Swedish :	Rotdödare

White ear caused by take-all

Early attack of take-all on wheat roots

Dark roots caused by a late attack

Black roots and stem base from a wheat plant with a severe attack of take-all

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