Net Blotch - Spot Form of Barley
Pyrenophora teres f. maculata
Drechslera teres is the Latin name of the imperfect stage.
Description:It starts as a small circular to elliptical dark brown spot becomes a parallel-sided elongated blotch up to 10 mm long which is often surrounded by a yellow halo especially near the tip of the blade.
Biology:Transmitted on Barley seed, residues (stubble) 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.
Reproduces by both asexual conidia and sexual ascospores.
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. 50% grain yield reductions in susceptible Barley varieties have been recorded.
(Murray and Brennan, 2009) estimated the potential yield loss to be 14%.
May reduce Barley quality
Management and Control:Sow resistant varieties. See HYPERLINK \l "_Disease_Susceptibility_of_Barley Va" Disease Susceptibility of Barley Varieties. Clipper and Stirling are moderately susceptible. Most other varieties are susceptible.
With time the fungus may mutate to affect previously resistant varieties.
Use clean 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 250 mL/ha propiconazole250 at flag leaf emergence provide some control but is often uneconomic.
Thiram is registered to control seed borne infections but these have not been found in Australia, so there is little point in using it for the Spot Form of Net Blotch.
Related and Similar Species:Net Blotch - Net Form (Pyrenophora teres f. teres)
Yellow Spot of Wheat (Pyrenophora tritici-repentis)
Halo Spot (Pseudoseptoria stomaticola)
Collated by HerbiGuide. Phone 08 98444064 or www.HerbiGuide.com.au for more information.