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Fungal Leaf Diseases of Barley and Fungicide Use in Barley (06/16/16)

Fungal pathogens are responsible for several leaf diseases of barley in North Dakota.

Fungal Leaf Diseases of Barley and Fungicide Use in Barley

Fungal pathogens are responsible for several leaf diseases of barley in North Dakota. Often times the fungal leaf diseases will appear as a complex, meaning more than one disease can be found on a leaf. The information below provides identification tips for common fungal leaf diseases of barley in North Dakota.

Net blotch (Pyrenophora teres teres, Pyrenophora teres maculata)

Symptoms: A light to dark brown spot will initially appear on the leaf surface. As the lesion matures, a net-like pattern will form within lesions (Figure 1). Eventually, lesions will combine and can cause severe defoliation (Figure 2).

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Important Information: There are two forms of net blotch that occur in North Dakota; net form and spot form. Distinguishing between the two forms can be very difficult when scouting fields and molecular techniques are needed for accurate diagnosis. Barley varieties vary in susceptibility to the two forms of net blotch. However, both forms of the disease will respond similarly to fungicides. The net blotch complex is a very common disease found throughout North Dakota.

Spot-blotch (Cochliobolus sativus)

Symptoms: Small dark brown spots will initially appear on the leaf. As the lesion matures, the lesions will become darker and more circular to elongated (Figure 3).

Important Information: Spot blotch is another very common disease found throughout North Dakota. The pathogen is also responsible for common root rot of small grains.

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Leaf Rust (Puccinia hordeii)

Symptoms/Signs: Orange-brown pustules full of dusty spores will be observed on the leaf surface and are often surrounded by a chlorotic halo.

Important Information: Rust pathogens tend to be very host-specific. For example, recently we have received several reports of stripe rust in the winter wheat crop. The pathogen responsible for stripe rust in winter wheat WILL NOT be able to infect barley. Similarly, the barley leaf rust pathogen will not be able to infect wheat.

Scald (Rhynchosporium secalis)

Symptoms: Leaf spots tend to be oval with a water-soaked appearance. Lesions eventually have a tan to bleach white center surrounded by a dark brown margin (Figure 4).

Important Information: Scald will be found periodically throughout North Dakota. It is less common to find scald compared to the other prevalent barley diseases.

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Fungicide Management

Once a fungal foliar disease has been identified, the next decision is to determine if a fungicide is needed. The decision to apply a fungicide will depend on growth stage, crop production practices, disease incidence in a field, canopy location of disease, yield potential, host resistance, upcoming weather events, etc. As a way to provide fungicide management information for barley growers, the Carrington Research and Extension Center has conducted fungicide efficacy and timing trials on barley for several years. Two years of data have been compiled (2014 and 2015) to summarize the effects of fungicides on flag leaf diseases and DON management. Most of the foliar diseases observed in these trials were net blotch and/or spot blotch. Only DON data from the 2014 season is included.

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Under the disease environments in 2014 and 2015, a fungicide application made at full-head with Prosaro or Caramba adequately managed flag leaf diseases and reduced DON (mycotoxin) levels. Although Evito (strobilurin chemistry) at full-head reduced flag leaf diseases, it had higher DON levels than the non-treated control. Similarly, fungicide applications made at flag leaf did offer flag leaf disease suppression but did not suppress DON. In most cases, a fungicide made at full-head had similar yield values when compared to the multiple fungicide treatment (flag leaf and full-head). These results provide a good snapshot of fungicide use in barley, but remember that most fungicide decisions for foliar diseases are best made using a scout-based approach. If a foliar disease epidemic occurs in the early vegetative leaf stages, two fungicide applications may be warranted. Also, it is important to select the appropriate chemistry (FRAC 3, triazole) when applying a fungicide at full-head for management of flag leaf diseases, Fusarium head blight and DON.

 

Andrew Friskop

Extension Plant Pathology, Cereal Crops

 &

Blaine Schatz

Carrington Research Extension Center-Director and Agronomist

 

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