The monoclonal antibody technology has provided a means to produce a supply of highly specific uniform antibody which is useful in the detection of plant viruses and which facilitates disease resistance screening. Because of the specificity of a monoclonal antibody to an epitope, a monoclonal antibody may not react to a partially degraded protein. Wheat streak mosaic virus (WSMV) is a member of the potyvirus group and is transmitted by the wheat curl mite Eriophyes tulipae Keifer. The capsid protein of WSMV, like many potyviruses, is degraded in planta. Monoclonal antibodies produced to WSMV reacted to native as well as trypsin treated virions. The antibodies were also useful for evaluation of hard red winter wheat cultivars inoculated with WSMV in the fall or in the spring under field conditions.