Yield losses can reach 60% when all plants in a crop become infected. Losses from CMV infection are greatest when seed with >1% infection is sown, aphids arrive early and widespread plant infection occurs.
The outcome of sowing seed infected with different levels of CMV varies greatly from year to year and site to site. Sowing seed with a high level of infection, which develops many in-crop sources, together with an early arrival of aphids initiates substantial early epidemics resulting in high disease incidence, reduced yield and increased infection in harvested seed. By contrast, with a dry start to the growing season, sowing seed with a high level of infection results in minimal yield loss and reduction in infection levels in harvested seed. The aphids arrive much later, resulting in a much reduced CMV spread.
|Initial CMV seed infection level||5%||0.5%||5%||0.5%|
|Aphid arrival||Early||Early||Very late||Very late|
|Final crop infection||89-95%||34-53%||1-2%||0.1%|
|Harvested CMV seed infection level||12-13%||7%||0.6%||0.1-0.2%|
ns=yield impact is not statistically significant
Influence of weather
The date of first arrival of aphids flying from pastures into crops is directly related to the magnitude of rainfall events in late summer and early autumn. Rainfall stimulates plant growth before the growing season, providing hosts (clovers, weeds and volunteer crop plants) that encourage rapid aphid multiplication. When lupin crops emerge, aphid flights invade them early and spread CMV from seed-borne infected seedlings to healthy ones which initiates early spread of CMV. When there is little or no summer or autumn rain, few plants are available to support aphids before crops are sown. Aphids take much longer to build up and arrive much later so CMV spread starts much later. In low risk areas, this scenario occurs more frequently than in high risk areas.
An integrated disease management approach is needed to control CMV in lupin crops, one which uses a range of control measures.
- Sowing healthy lupin seed. This is the most important measure. A representative seed sample is tested to determine the level of infection. In low risk areas, seed with <0.5% infection can be sown without undue risk of yield loss. Seed infection of <0.1% (a zero result from a 1000 seed test) is recommended for grain crops in high risk areas, and for seed certification crops in any rainfall zone. Seed testing can be done through AgWest Plant Laboratories, South Perth.
- Sow early at high seeding rates using narrow row spacing to promote early crop canopy coverage. This deters aphids from landing and shades over the seed-infected and early infected plants, denying aphids access to them.
- Direct drill into retained stubble. Ground cover reduces aphid landing rates before a crop canopy develops, especially with wide row spacing.
- Isolate from neighbouring lupin crops.
- Maximise weed control. This reduces spread of CMV from lupins to weeds and then from weeds back to lupins.
Note: Insecticides applied to crops are ineffective at controlling CMV.