Diseases of oats
|Septoria avenae blotch||Phaeosphaeria avenaria f.sp. avenaria|
|Stem and leaf rust||Puccinia graminis var. avena|
|Leaf spot||Drechslera campanulata|
|Bacterial blight||Pseudomonas syringae pv.striafaciens|
|Yellow dwarf||Barley yellow dwarf virus|
1. Septoria avenae blotch — Phaeosphaeria avenaria f.sp. avenaria
The fungus infects leaves, sheaths and stem and may also infect heads. Symptoms begin as mottled light and dark brown blotches, with dark brown centres. They are restricted and distinct at first but may enlarge to cover most of the leaf. Lesions in the leaf sheath extend into the stem causing death and blackening which may lead to lodging. The fungus sometimes causes a dark discolouration of the grain when unseasonably late rain occurs.
Mode of Spread & Survival
- Infected stubble is the main source of survival of pathogen.
- The sexual stage of the fungus, Phaeosphaeria avenaria, occurs on infested stubble and produces ascospores which are spread to moderate distances by wind.
- Avoid continuous oat cultivation.
- Stubbles from diseased plants should be destroyed by burning or ploughing.
- Prophylactic spray with common fungicides helps to manage the disease.
2. Stem and leaf rust — Puccinia graminis var. avena
The disease appears as elongated reddish-brown pustules mainly on stem but also on leaves and heads. The powdery spore masses in the pustules can dislodge readily.
Mode of Spread & Survival
- The fungus is carried over on volunteer oats and wild oats from season to season.
- The pathogen also survives in plant debris.
- Grazing, or ploughing may help to control volunteer and wild oats. But the effect could be limited because of the abundance of wild oats.
3. Yellow dwarf – Barley yellow dwarf virus
The disease first appears three to five weeks after infection as yellow-brown or orange-brown, diffuse blotches near the leaf tip. The blotches enlarge and fuse until most of the leaf is affected and appears orange-brown. Later it changes to crimson-pink which is recognised easily in the field. Affected Oats seedlings may show additional symptoms of severe stunting, increased tillering and floret abortion. Infection after tillering causes a characteristic ‘reddening’ of late emerging leaves and tip-reddening and death of older leaves.
Mode of Spread &Survival
- Infection is spread from the grass reservoirs to oats and aphids.
- The virus survives between growing seasons in grasses which persist through the summer.
- BYDV is always more severe following wet summers when aphid survival and build-up has occurred, because of the role of aphids in establishing infection.
- Roughing and vector control helps to reduce the incidence. Also volunteer plants/weeds should be eradicated to reduce the inoculums.