Leaf Rust of Wheat

Puccinia recondita

Description:

Light brown, oval pustules, full of powdery spores appear on the topside of the leaf blade in late winter to spring. These may extend to the leaf sheath late in the season. Black pustules are formed on older leaves in spring to summer.
The light brown spores will rub off the leaf onto your finger rubbed. The black spores at the end of the season don't rub off.
Check the oldest green leaves for early infections.

Species Affected:

Wheat, Cereal Rye, Durum Wheat.

Biology:

Requires a green host to survive from one season to the next. It does not survive on stubble or in the soil.
Favoured by moist conditions with temperatures between 15 and 220C.
Early sown crops may be infected as seedlings which help spread it in spring to later sown Wheat.
Resistant varieties may be susceptible to new strains of Leaf Rust.
The light brown spores are infectious whereas the black spores aren't.

Life Cycle:

Infected autumn crops lead to a build up of spores that may cause an epidemic in early and late sown crops.

Origin and History:

Distribution:

Significance:

Management and Control:

Rarely causes economic losses in WA and control rarely needed.
Sow resistant varieties.
Use a seed treatment to reduce early infections especially on early sown crops. These typically give 8-12 weeks protection.
Spray at the first signs of infection and repeat in 4 weeks if necessary. Timing is critical to achieve economic results.
Control volunteer and out of season Wheat at least 4 weeks before planting crop.
Make a plan with neighbours to reduce risk factors.

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 then apply a fungicide immediately to protect the flag leaf.

Related and Similar Species:

Stem Rust of Wheat (Puccinia graminis)
Stripe Rust of Wheat (Puccinia striiformis)
Leaf Rust of Barley (Puccinia hordei) looks very similar but occurs on Barley.
Leaf Rust of Oats (Puccinia coronata f.sp. avenae) looks very similar but occurs on Oats.
Leaf Rust of Rye looks very similar but occurs on Rye.

References:

1293

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.HerbiGuide.com.au for more information.