Net Blotch - Net Form of Barley
Pyrenophora teres f. teres
Drechslera teres is the Latin name of the imperfect stage.
Description:Initially a small circular to elliptical dark brown spot that elongates to fine dark lines along and across the leaf blade forming a net like pattern. With time the lesions become elongated and darker and often with a yellow margin. Severely infected leaves wither quickly. It can also infect the heads when severe.
Species Affected:Barley, Barley Grass.
Biology:Transmitted on Barley seed, residues and occasionally on Barley Grass residues.
Spores from residues infect adjacent plants and may be carried by wind.
Moist, warm (15-250C) conditions favour infection.
Humid conditions after flowering may allow the disease to infect the grain.
Infected residues can produce spores for over 2 years.
Life Cycle:Origin and History:
Usually only in paddocks where Barley is regularly grown.
More common in the medium to high rainfall areas.
Significance:Generally only a problem where barley is grown on paddocks with infected stubble. Yield losses of up to 30% may occur in these situations if susceptible varieties are sown. (Murray and Brennan, 2009) estimated the potential yield loss to be 26%.
Management and Control:Sow resistant varieties. See HYPERLINK \l "_Disease_Susceptibility_of_Barley Va" Disease Susceptibility of Barley Varieties. Clipper is resistant. Forrest, O'Connor and Stirling are moderately resistant.
With time the fungus may mutate to affect previously resistant varieties. Skiff, Schooner and Sloop appear to have lost some of their resistance in recent years.
Use clean seed.
Thiram reduces disease carry over on infected seed.
Avoid areas where Barley or Barley Grass residues are present.
Burn or bury stubble.
Adjust rotations so there is a longer period between Barley crops.
Infection is usually more severe in early sown crops.
Control Barley Grass in pastures and crops,
Foliar applications of propiconazole provide some control but are often uneconomic.
Seed dressings and in furrow treatments are generally not effective stubble borne net blotches. Difenoconazole plus metalaxyl-M (e.g. Dividend) will control seed borne infections but these are generally of little significance in WA.
Related and Similar Species:Net Blotch - Spot Form (Pyrenophora teres f. maculata)
Yellow Spot of Wheat (Pyrenophora tritici-repentis)
Halo Spot (Pseudoseptoria stomaticola)
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