Smutted barley and what it means for management

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The following article is taken from the latest blog by Catherine Garman, who manages disease research at AHDB.

Higher than normal levels of loose smut (caused by the fungus Ustilago nuda f.sp.hordei) are being reported in winter barley crops across the UK. These reports have been from crops grown from certified and seed-treated seed, not just from home-saved seed.

Loose smut is easily recognised at ear emergence, as each grain is usually completely replaced by a mass of black fungal spores. Spores are released from infected ears and are carried by the wind to the open flowers of surrounding healthy plants. There they germinate and the fungus grows into the developing grain site. Once this seed is replanted, the infection grows, initially without symptoms, with the disease only visible once the ear emerges.

Loose smut not only causes yield loss but smutted ears will rapidly spread the infection to surrounding crops, which won’t show their infection until the next spring (if the seed is replanted). However, the severe symptoms of loose smut can make the problem seem worse than it actually is: an infection of 0.1 per cent (1 in 1000 ears affected) looks dramatic but would only give a yield loss of 0.1 per cent.

The disease levels reported this season could be the result of a number of things:

> Higher levels in seed. However, testing by the Official Seed Testing Station (OSTS) has shown that levels in certified seed used for drilling in autumn 2017 were no higher than in the previous three years

> Increased numbers of volunteer barley (ie crops grown from untreated seed)

> More favourable conditions for infection spread in spring 2017 (eg windy during flowering and a prolonged flowering period)

> Resistance to fungicidal seed treatments. These problems are being seen over a range of manufacturers’ products and active ingredients. Testing is ongoing to investigate this and results won’t be available for several months.

For drilling in autumn 2018, growers can minimise risk of loose smut by not home-saving seed that has signs of infection or from crops close to a heavily infected crop. The safest bet in this situation is to use certified seed treated with a seed treatment that has loose smut on the label.

The main fungicidal seed treatments for winter barley are Redigo Deter (clothianidin + prothioconazole), Redigo Pro (prothioconazole + tebuconazole), Raxil Star (fluopyram + prothioconazole + tebuconazole) and Rancona 15 ME (ipconazole). Foliar fungicide treatments do not control loose smut.

Varietal resistance to loose smut is not tested in the AHDB Recommended List, but varieties with an open flowering habit and longer flowering time can be more at risk, as the longer the florets remain open, the longer the time the plant is susceptible to infection.

Wheat and oats are also affected by loose smut but by a different pathogen, meaning high levels in barley do not confer risk of higher levels in wheat and oats.

Spring barley is just coming into ear, so any problems in this crop will soon become apparent. Monitoring loose smut levels in winter and spring barley crops now and in spring 2019 will indicate if the problem is worsening on your farm.

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