Bean yellow mosaic virus (BYMV)
Bean yellow mosaic virus (BYMV) causes a serious disease in lupins which is found predominantly in high rainfall wheatbelt zones It is not seed-borne in narrow-leafed lupins, but survives and builds up in clover pastures. It is transmitted from infected clover plants to lupin crops by aphids. Disease risk is usually highest in seasons with summer/autumn rain promoting early build-up and migration of aphids. Crops neighbouring clover based pastures or containing clover weeds are at greatest risk of infection.
Symptoms
In narrow-leafed lupins, symptoms start with necrotic streaking from the youngest shoot, which bends over causing a characteristic shepherds’ crook. The growing tip dies and the leaves become pale, wilt and fall off. Necrotic streaking and blackening then spread throughout the stem causing the plant to die. In later infections the necrotic symptoms may remain restricted to sections of the plant close to the site of infection and may cause black pods (black pod syndrome) and shrivelled seed on the main stem and affected branches. Dependent upon variety, Albus lupin can either express classical mottling and stunting symptoms or stunting and necrotic streaking similar to narrow leafed lupin.
Management
- Eliminate clover regrowth under lupin crops and avoid sowing adjacent to clover based pastures.
- Deter aphid landing by reducing bare ground exposure through promoting early canopy development and sowing into retained stubble.
- Differences are evident between varieties in expression of black pod symptoms associated with late BYMV infection.
