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Tan Spot

Tan Spot

Tan Spot

Pyrenophora tritici-repentis (Dreschslera tritici-repentis) 

Pathogen

Fungus

Hosts

Wheat, barley , rye

Symptoms

Initially seen as light brown flecks which are difficult to positively identify and these develop into the more characteristic symptoms of diamond or oval shaped lesions which are tan coloured with a surrounding yellow halo and a dark spot in the centre. These lesions are very similar to Septoria nodorum but they can be differentiated by molecular diagnostics. As the lesions enlarge they coalesce to produce larger areas of dead leaf tissue.
After harvest raised pseudothecia fruiting bodies can clearly be seen on the crop stubble. To the touch these give the stems a rough `sandpaper` like feel.

Development

Spores from these pseudothecia release ascospores which are dispersed by wind or rainsplash. After successful invasion of plant tissue further spread within the crop, or adjacent fields, is by means of conida (a different spore type) which are also spread by wind or rainsplash. Prolonged leaf wetness is necessary for successful germination and infection of a host leaf.
The disease can also be seed-borne.

Favourable Factors

Prolonged, warm, wet weather with prolonged leaf moisture (for periods of up to 24 hours).

Importance

Commonly occurring in countries such as Denmark and France and widespread outbreaks were reported in Scotland in 2010 and 2011. Yield losses of nearly 50 % have been recorded from countries overseas such as the USA.

Control

• Disease free seed
• Varietal tolerance
• Avoid minimal cultivation and dispose of crop debris and volunteers
• Use of an effective fungicide programme particularly at the later T2 timing. 

Tan Spot A1 CibTan spot
Tan Spot CibWell developed leaf lesions
Tan Spot A2 LibSevere infection
Tan Spot A1 LibClassic leaf lesions

Identification and Management of cereal diseases

Find out more information on the key disease threats to your cereal crop. For each disease you will find out the importance of the disease in terms of potential yield penalty, how to identify the disease in its early stages and our advice on the best control strategies.

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