Substantial reductions in snap bean yield and quality throughout the northern US and Canada have been associated with viruses over the past several years. Alfalfa mosaic alfamovirus, Cucumber mosaic cucumovirus, Bean common mosaic potyvirus, and Bean yellow mosaic potyvirus were prevalent in New York snap bean fields in 2002. Alfalfa is a host of these viruses and may be a major source for these viruses that spread into snap bean fields by winged aphids. In 2002, snap bean plants infected with viruses in fields that were adjacent to alfalfa tended to be more aggregated than those in fields relatively isolated from alfalfa, indicating that viruses were initially acquired within the bean field and then were spread secondarily to nearby plants. The pea aphid and yellow clover aphid were the most common species encountered in early and late snap bean plantings, respectively. Surprisingly, the incidence of virus-infected snap bean plants in fields adjacent to alfalfa and those isolated from alfalfa did not differ. Perhaps, a source of viruses in addition to alfalfa also exists (e.g., infected seed), which would explain why very high levels of virus-infected plants were observed in all snap bean fields. The number of pea aphids and yellow clover aphids dispersing into snap bean fields that were adjacent to alfalfa did not differ from numbers of those in isolated fields. Perhaps, aphids migrate from alfalfa into snap bean fields, regardless of the proximity between alfalfa and snap beans, resulting in equivalent levels of virus infection in all snap bean fields.
Species 1: Homoptera Aphididae Acyrthosiphon pisum (pea aphid)
Species 2: Homoptera Aphididae Therioaphis trifolii (yellow clover aphid)
Keywords: aphid-transmitted virus
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