Little known virus carried by bean leaf beetles causing new soybean losses

WOOSTER, Ohio – Ohio soybean growers are getting hit hard this season.

First there was the soybean aphid, a relatively new insect that has been feeding on the plants. Then reports came that the two-spotted spider mites were on the move.

Now there’s a new virus in the air that may cause additional headaches.

The bean pod mottle virus, seen throughout the Midwest last year, is a little-known virus spread by a familiar insect – the bean leaf beetle.

“Last year there were a lot of reports across the Midwest and Ohio that suggested the presence of this soybean virus,” said Ron Hammond, an Ohio State University entomologist. “We figured we are seeing the virus more because we are seeing more of its primary vector, the bean leaf beetle. The insect has become more common over the years, partly due to the increase in early planting of soybeans.”

Still an unknown. Hammond said the presence of the virus is causing concern for growers because it causes reduction in seed quality and yield, and researchers know very little about it and how the insect acquires the virus and spreads it from field to field.

One of the main symptoms of the virus is green-stem syndrome, where the plant stem remains green right up to harvest.

Bean pod mottle virus also produces similar symptoms as soybean mosaic virus, a common virus that can be spread by the soybean aphid, a new insect found in Ohio just last year.

“Not only are we concerned about the soybean aphid transmitting the soybean mosaic virus, but now we have to contend with bean pod mottle virus,” said Hammond. “We may be getting into a situation where we are may see two different insects capable of transmitting two different viruses that produce the same symptoms in the plant.”

Monitoring fields. OSU researchers, in collaboration with scientists from the U.S. Department of Agriculture, are monitoring 20 fields in nine locations throughout Ohio to determine what generation of the bean leaf beetle is carrying the virus, how the insect is spreading the virus, and what impact the virus has on soybean yields.

Hammond said the bean leaf beetle goes through three generations.

An over-winter generation emerges from May to late June and lays eggs in soybean fields. The first generation then emerges in mid to late July; and the second generation in mid to late August. The second generation then over-winters into the following year.

“We are just starting the see the first-generation insects emerging in soybean fields right now,” said Hammond.

Too late now. Growers can do little to protect their plants from the virus at this stage in the growing season.

“If the virus is present, it would have gotten into the fields in early spring,” said Hammond. “Right now, we are not even making any recommendations for spraying the over-winter generation because we don’t know if that is effective or not.”

“I know that some growers sprayed their fields against the over-winter generation, so we are going to monitor those fields to see how well that worked out.”

Plant later. An alternative control method that researchers suggest may be effective is to plant late in the season.

“When the over-winter generation emerges, they head for the plants that are already out of the ground. Those are the early plantings of late April or early May,” said Hammond.

“But if a grower plants late, like mid to late May, then his fields might escape the insect and perhaps the virus altogether. It’s not 100-percent effective, but it probably is the first line of defense against the insect and would reduce the amount of the virus coming into the field.”