Leaf Rust of Oats
Puccinia coronata f.sp. avenae
Description:Yellow orange small circular to elongated pustules, full of powdery spores appear on the upper side of the leaves. Later in the season pustules may appear on the sheaths and heads. Black spores appear predominantly on the under side of the leaf as the disease progresses.
The yellow orange spores will rub off the leaf onto your finger rubbed. The black spores at the end of the season don't rub off.
Species Affected:Oats, Wild Oats.
Biology:Requires warm (15-220C), moist conditions for infection. Spores germinate within 12-24 hours of receiving moisture.
The yellow orange spores are infectious whereas the black spores aren't.
It requires a green host for survival.
Autumn sown crops, when nights are warm, are often severely affected and responsible for infecting later sown crops in spring.
Life Cycle:Origin and History:
It can cause up to 50% loss in hay and grain yields but in most cases loss of grain yield is slight and the major economic effect is loss of marketability of export hay.
It may also affect the palatability and marketability of hay.
Management and Control:Sow resistant varieties.
Control volunteer and out of season Oats.
Control Wild Oats.
Avoid out of season plantings.
Foliar spraying must be done early and usually provides about 4 weeks protection.
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 in grain crops.
Fungicide Resistance:None reported.
Related and Similar Species:Stem Rust of Oats (Puccinia graminis f.sp. avenae) has darker, larger pustules that rupture the tissue surface and are more common on the sheath and stem.
Leaf Rust of Wheat (Puccinia recondita)
Stripe Rust of Wheat (Puccinia striiformis)
Other diseases and nutritional disorders don't have yellow orange spores that rub off the leaf.
Collated by HerbiGuide. Phone 08 98444064 or www.HerbiGuide.com.au for more information.