Prevention and Control

It is possible to eradicate BCMV and BCMNV from a particular production region, or at least to significantly reduce primary inoculum, by eliminating susceptible genotypes and planting only resistant varieties. There are few important noncrop reservoirs of inoculum, and infected seed are responsible for primary infections in the crop.

Rogueing of symptomatic plants is not recommended as a means of control, as it is highly likely that systemi-cally infected plants without significant symptoms will remain to act as significant reservoirs for secondary infection by aphid transmission.

Exclusion of the virus is highly effective in areas where the virus is not present, but this may preclude introduction of new germplasm or cultivars without effective resistance. One or both viruses are almost universally present in seed lots of varieties that do not carry the I gene, and the majority of Latin American land race types do not possess any of the strain-specific recessive resistance genes. Most cultivars derived through extensive breeding programs carry the dominant I gene for resistance to BCMV and BCMNV. Increasingly bc-3 is being combined with I to yield cultivars with effective resistance to both BCMV and BCMNV.

Certified seed can be an effective means of control. A certified seed program in California with a limit of <0.5% BCMV has aided in the control of the disease, as resistant varieties are not yet available for all bean classes currently grown in California. Monitoring of BCMV for certification also aided in identification and containment of an outbreak of BCMNV introduced in seed of a navy bean cultivar.

Vector exclusion may aid in control, but as aphids rarely colonize common beans, migratory aphids are responsible for most transmission in many areas. As BCMV and BCMNV can be acquired and transmitted in less than 1 min access to plants, insecticide treatment is unlikely to prevent, and may even encourage vector movement and transmission. Vector control through insecticide application may be effective in parts of Africa and Asia where aphids do colonize beans. Oil sprays are known to reduce transmission ofstylet-borne viruses such as BCMV and BCMNV, but their lack of systemic action, and thus need for frequent reapplication to a growing crop, reduces the cost-effectiveness of their use.

See also: Potyviruses.

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