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Control thresholds for seedborne diseases

Microdochium seedling blight (Microdochium nivale) HGCA photos

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Treatment recommended if more than 15% of grain is infested

Treat if exceeded 30 % Fusarium spp + M. nivale+ Stagnospora

In preparation

Treat if over 10%

No threshold (but reinforced protection recoommanded if over 15%)

In preparation

In preparation

In preparation

The most common symptom of a serious attack is poor establishment. The fungus can also cause root rotting brown foot rot, leaf blotch and in combination with Fusarirum species, ear blight. It is regarded as the most common cause of seedling blight and sowing seedlots with high levels of infection causes very poor crop establishment leading to yield loss. Infected grain with inoculum mainly follows wet seasons with high levels of fusarium head blight. During such seasons spores are spread by splash from stembase up the plant and ultimately infect the ear. Inoculum is also found in the soil. Infections from infected seed are increased following late sowing. For DK: recommended thresholds for conventional farming in DK. For organic farming these thresholds are obligatory

 

Glume blotch Septoria nodorum (Stagonospora nodorum)

 HGCA photos

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Treatment recommended if more than 15% of grain is infested

Treat if exceeded 30 % Fusarium spp + M nivale+ Stagnospora

In preparation

Treat if over 10%

In preparation

In preparation

In preparation

In preparation

The disease is quite rare in many parts of Europe these days. Since the significance of this disease has dropped since the beginning of the 1980th. The severity depends on precipitation in the season where the seed is produced. However at high levels crop establishment can be badly affected. The most common effect is poor plant establishment; Symptoms are so similar to those of Microdochium seedling blight that only laboratory analysis can distinguish tham. Septoria nodorum is more commonly associated with necrotic blotching of leaves and glumes Although the disease can survive on plant debris, most infections result from seed born inoculum. Risk factors are high seed infection levels combined with cool and wet condition. Many seed treatments are known to be effectively controlling this disease. For DK: recommended thresholds for conventional farming in DK. For organic farming these thresholds are obligatory

 

Common bunt (Tilletia tritici) HGCA photos

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0 spores in C1, 10 spores in C2

1 spore/ seed or more

In preparation

1 spore/seed or more

In preparation

In preparation

In preparation

In preparation

Symptoms appear after ears emerge. Plants are often stunted and sometimes have yellow streaks along the flag leaf. Infected ears are dark grey-green with slightly gaping glumes. Bunt balls replace all grains and if broken release millions of black spores smelling of rotten fish. Spores on the seed surface germinate with seeds. After invading shoots and growing points, the fungus grows within the plant until ear emergence when bunt balls replace grain. The spores are mainly spread during harvest and contaminate healthy grain. Spores can also land on soil and spread by wind to neighboring fields. Soil-borne spores can invade seedlings very early in germination. Seed born infections are mainly seen when farmers have used farm-saved seed for several generations. The infection increases under conditions, which give rise to slow emergence. Soil born inoculum is only seen as a risk factor, when wheat is sown after wheat. Short and dry intervals between harvest and sowing increase the risk. Cultivar resistance has been found in several cultivars. Tilletia foetida is occasionally found in some countries. This disease is very similar to Tilletia caries. Spores are however slightly different in shape.For DK: recommended thresholds for conventional farming in DK. For organic farming these thresholds are obligatory

 

Ergot (Claviceps purpurea) HGCA photos

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No official recommendation for seed treatment

No seed treatment

In preparation

1 piece /1000g HVS

No official recommendation for seed treatment

In preparation

In preparation

In preparation

In some cases a hard purple black sclerotium up to 2 cm long, replaces some grains in the ear. Yield is normally not affected but ergot is highly poisonous to man an animals, so contaminated grain will be rejected or require cleaning. Standard requirements are given for certified seed. The ergots survive from season to season as dormant sclerotium place on the ground. In summer it will germinate and produce spores which by wind will spread to the open flowering grasses or cereals. For DK: recommended thresholds for conventional farming in DK. For organic farming these thresholds are obligatory

 

Loose smut (Ustilago tritici) HGCA photos

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No threshold

No threshold, very rare disease

In preparation

0,2% HVS

No threshold

In preparation

In preparation

In preparation

For DK: recommended thresholds for conventional farming in DK. For organic farming these thresholds are obligatory

 

General principles used for assessing diseases

Disease

Method

Results given as

Common bunt 1. Wash
2. Molecular test
Spores per seed
Over or under 1 spore/seed
Microdochium seedling blight 1. Agar plate
2. Molecular test
% infection
Either over or 1 spore /seed
Septoria and fusarium seedling blight Agar plate % infection
Ergot Visual after search in ½-1 kg seed Number of pieces per ½ or 1 kg
Loose smut Embryo extraction % infection in embryo (1000-2000 tested)

 

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Revised 09.06.2017