Net Blotch

Pyrenophora teres (asexual Drechslera teres)

Biology

Net blotch is a common, destructive foliar disease of barley in western Canada, second only to scald as a cause of yield loss. Net blotch is more common than scald in the warmer, drier regions of the prairies.

The fungus overwinters on the seed or crop residue. Spores are produced and spread by wind and rain. Spores produced on infected plants are mainly responsible for destructive, secondary spread of the disease within the crop.

Seedling infection is greatest during periods of cool humid weather (10-15 degrees Celsius). Spore production and infection of the growing crop is favoured by high relative humidity and temperatures around 20 degrees Celsius.

Damage Description

Light brown spots with distinctive dark brown net-like patterns appear on the leaves, sheaths and glumes. Spots enlarge and join into dark brown stripes. There is also a spot-producing form of this fungus that produces dark brown spots surrounded by a yellow zone. Symptoms vary with the variety and weather.

Yield loss is proportional to the amount of leaf area destroyed on the upper two leaves. The average yield loss in Alberta is about 1.5 per cent. Losses of 50 per cent and more have occurred in highly susceptible varieties such as Elrose. Net blotch lowers grain yield and brewing quality by reducing the carbohydrate content of kernels.

Diagnosis

Use the barley scald assessment procedure to obtain an indication of crop loss.

Management Strategy

• Use resistant cultivars. Use resistant cultivars. See Varieties of Cereal and Oilseed Crops for Alberta for more information.
• Bury crop residue and destroy volunteers.
• Use balanced applications of nitrogen and phosphorus. Heavy nitrogen applications generally produce conditions favourable to outbreaks of this disease.
• Follow a crop rotation for at least two years with non-susceptible hosts. Barley should not follow barley, particularly if disease levels were high the previous year.
• If barley must be grown in two successive years, use a susceptible cultivar the first year and a resistant type the second.
• Use disease-free seed if possible. Seed may be sent to the Agriculture Canada Seed Laboratory in Ottawa to determine the percentage of infection.
• Control the seed-borne phase of net blotch with a chemical treatment.
• Apply a foliar spray. Tilt 250E/Bumper 418EC (propiconazole) and Headline EC (pyraclostrobin) are registered on barley in Canada for effective control of net blotch and scald.

Net blotch of Barley - some netting but most infection occurs as long elongated stripes.

Net blotch - note typical netting and premature yellowing of infected leaves.

Net blotch of barley, range of symptoms.

Net blotch of barley on the flag leaf - cause of major yield loss.

Net blotch of barley and some infection interaction both with spot blotch (common root rot fungus).