Leaf Rust of Barley
Light brown, oval to circular pustules, full of powdery spores appear on the topside of the leaf blade and sheath in late winter to spring. These are usually surrounded by a light green to yellow halo. Black pustules are formed on older leaves in spring to summer.
The light brown spores will rub off the leaf onto your finger when rubbed. The black spores at the end of the season don't rub off.
Species Affected:Barley, Barley Grass, Star of Bethlehem (Ornithogalum umbellatum).
Biology:The light brown spores are infectious whereas the black spores aren't.
It requires green material to survive over summer or an alternate host like Star of Bethlehem (Ornithogalum umbellatum) than can be infected by the over summering black spores.
New strains of rust appear commonly that may be damaging to previously "resistant" varieties.
Moist conditions and temperatures around 150C favour the disease.
Early sown crops (when nights are still warm) are often more severely infected than later sown crops.
It reproduces sexually on Star of Bethlehem (Ornithogalum umbellatum) which gives it the potential to quickly develop resistant strains.
It normally reproduces asexually where mutations can lead to resistant strains but at a much lower probability.
Life Cycle:Caries over from one season to the next on volunteer Barley or Star of Bethlehem (Ornithogalum umbellatum) and occasionally on Barley Grass.
The yellow orange spores are infectious whereas the black spores aren't.
Origin and History:In 1991 it became tolerant to the resistance genes in Gairdner, Fitzgerald, Baudin, Tallon and Lindwall.
Distribution:Found in all Barley growing regions of Australia.
Significance:(Murray and Brennan, 2009) estimated the potential yield loss to be 16%.
Management and Control:Sow resistant varieties. HYPERLINK \l "_Disease_Susceptibility_of_Barley Va" Disease Susceptibility of Barley Varieties.
Use a seed treatment to reduce early infections for 8-12 weeks. These are most useful for early sown crops.
Don't plant Barley in paddocks infested with Star of Bethlehem or destroy infected Barely crop residues in these paddocks if they must be planted.
Spray at the first signs of infection and repeat in 4 weeks if necessary. Timing is critical to achieve profitable results.
Control volunteer and out of season Barley and Barley Grass.
Control Star of Bethlehem and don't plant Barley in these areas.
Fungicide Resistance:None reported.
Thresholds:Randomly select 25 tillers over the paddock. If more than 2 tillers are infected then spraying could be worthwhile especially in good crops and where the disease has appeared early.
On susceptible varieties at full flag leaf emergence, if rust covers more than 5% of F-1 or F-2 (the two leaves below the flag leaf) and the crop yield potential is greater than 2 t/ha and/or the crop is malting quality, then apply a fungicide immediately to protect the flag leaf.
Related and Similar Species:Leaf Rust of Wheat (Puccinia recondita)
Stem Rust of Barley (Puccinia graminis f.sp. secalis)
Stem Rust of Barley (Puccinia graminis f.sp. tritici)
Stem Rust of Wheat (Puccinia graminis f.sp. tritici)
Stripe Rust of Wheat (Puccinia striiformis)
Stripe Rust of Barley has not been recorded in Australia.
Stripe Rust of Barley Grass was introduced and discovered in 1998 and will infect Barley but hasn't cause yield losses.
Collated by HerbiGuide. Phone 08 98444064 or www.HerbiGuide.com.au for more information.