Snap bean production is an important part of the procession crop landscape in Wisconsin.
Normally we don’t concern ourselves with virus-related problems. While the literature includes a
list of virus pathogens capable of infecting snap beans, we normally don’t see more than a few
symptomatic plants in any given year. Usually those plants with symptoms are located near the
field margins where aphids carrying viruses such as bean yellow mosaic virus are most likely to
land, feed and transmit the style -borne virus. All this changed in 2000 with the arrival of the
soybean aphid in such large numbers that suddenly processor field personnel were treating
commercial snap bean fields for aphid control, something they rarely if ever has to previously
confront. During the 2000 cropping season, Symptoms of virus infection were observed on
commercial fields of snap beans in southeastern and eastern WI. This widespread outbreak
affected the yield and pod quality of snap beans and ultimately led to the loss of several hundred
acres of production. Two viruses, alfalfa mosaic virus (AMV) and cucumber mosaic virus
(CMV), both aphid transmitted in a stylet-borne manner) were found to be the primary incitants
of the observed symptoms. The timing and distribution of the soybean aphid was associated with
virus outbreaks on snap beans. During 2001, these same viruses were again associated with
symptomatic snap bean plants. The majority of production fields with virus-like symptoms in
2001 were planted in late June through the middle of July and the worst affected plantings were
located along Lake Michigan in NE Wisconsin. Data collected in research plots at the West
Madison Ag Research Station indicated differences in the severity of symptom expression among
50 plot entries representing most breeding programs in the U.S. Greenhouse inoculation studies
confirmed that several lines were tolerant of AMV and CMV. Data colle cted during 2001
provided the basis for expanded field trials during 2002.