Is that soybean mosaic virus or herbicide injury?
click image to zoomCraig GrauFigure 1. Mosaic symptoms on soybean caused by Soybean mosaic virus. Calls, photos, and plant samples have been coming in over the last week or so with soybeans exhibiting abnormal growth including leaf cupping and strapping. Some of the symptoms look very similar to soybean mosaic virus (SMV) giving the leaves a somewhat bumpy and rippled appearance (see Fig. 1). However, further investigation has yielded clues that the cause of the symptoms is not SMV. Samples coming into the diagnostic lab are actually lacking few symptoms of virus but exhibiting symptoms of growth regulator herbicide injury.
click image to zoomCraig GrauFigure 2. Mosaic symptoms on a soybean caused by Alfalfa mosaic virus. There have been several viruses identified in soybean fields this season in Wisconsin. Alfalfa mosaic virus (AMV; Fig. 2) and Bean pod mottle virus (BPMV; Fig 3) have both been observed in soybean fields. However, SMV has not yet been identified. This isn’t to say that SMV isn’t out in fields in Wisconsin, we simply haven’t seen symptoms or positively identified the presence of the virus. Keep in mind the following points about these three viruses of soybeans:
Soybean mosaic virus
Soybean mosaic virus can be transmitted in seed (Hill, 1999). Aphids can also transmit SMV. Yield loss from SMV infection can be as high as 66-86% in susceptible cultivars (Hill, 1999).
Symptoms of SMV can vary from leaf deformation, to more pronounced mosaic symptoms, and reduced pod yield or malformed pods. Symptoms can be less severe at moderate temperatures (~75 F) and non-existent at high temperatures (>86 F). Management includes using SMV-free seed and also planting late.
Alfalfa mosaic virus is transmitted in low levels in soybean seed (Tolin, 1999). Aphids transmit AMV. Symptoms of AMV can vary from localized dead lesions on leaves, to large areas of yellowing. The impact of AMV infection on soybean yield is unknown (Giesler and Ziems, 2006).
Bean pod mottle virus
Bean pod mottle virus is transmitted in low levels (0.1%) in soybean seed (Gergerich, 1999). Some perennial weeds have also been found as hosts. Leaf-feeding beetles are vectors of BPMV. Beetles can acquire the virus during feeding and immediately transmit particles (Gergerich, 1999). Management of BPMV includes controlling broadleaf weeds at field edges, utilizing a trap crop for leaf feeding beetles at field edges, and resistant cultivars.