COLUMBUS – Environmental stresses, rather than disease pressure, may be why parts of Ohio are producing below-average soybean yields.
Ohio State University researchers found that the presence of diseases was not high enough to dramatically affect yields. They believe extremely dry conditions in parts of the state may be a contributing factor.
Stunted growth. “Stunting from root rot and drought conditions in parts of the state, like the north and northeast, affected yields this year,” said Anne Dorrance, an Ohio Agricultural Research and Development Center plant pathologist.
“The hardest message to get across to growers is that it’s difficult to assess yield loss this year when we’ve had such dramatic environmental conditions.”
For example, areas of heavy drought were also the heaviest for the soybean aphid,” Dorrance said. “It’s hard to separate what really is the cause-and-effect relationship.”
Yields vary. Soybean yields in drought-stressed northern Ohio are 30 percent to 50 percent below average, while southern Ohio is seeing record yields because of ample rainfall.
Yields are averaging 43 bushels per acre, according to a USDA estimate.
“In drought areas we surveyed, plants were barely to my knees, but in good areas the plants were up to my waist,” said Ron Hammond, research center entomologist. “We are expecting most of the state to have good yields.”
According to the USDA, 80 percent of soybeans have been harvested in Ohio.
Little disease. Reports of soybean diseases have been low to nonexistent. Hammond, who surveyed fields throughout the state, said the presence of diseases has been light.
“Green-stem syndrome is much lower this year than last year and not much of a problem,” Hammond said.
“Last year, that’s all growers talked about was green-stem syndrome,” Dorrance said. “We might have found it in 1 percent of the fields. This year we are not hearing anything so far. It’s very, very hard to find.”
The exact cause of green-stem syndrome is unknown. Parts of the mature soybean plant turn brown except for the stem, which remains bright green.
Green-stem syndrome can cause major reduction in yields because the green stem makes it difficult to mechanically harvest the pods, and pods are in the field during rainy periods where the seed develops secondary fungal infections.
Another type of “green-stem” condition where the plants remain green and the pods are malformed is caused by plant viruses such as bean pod mottle virus and soybean mosaic.
Populations of the bean leaf beetle, which spread the bean pod mottle virus, were low this year compared to last year, Hammond said. “Only two to three fields, at the most, had a noticeable level of pod feeding compared to what we found in previous years.”
Not sure why. “We had tremendous bean leaf beetle populations over the last two years, and this year the population just crashed,” Dorrance said. “That may be why bean pod mottle virus is very low this year, but we are not entirely sure why that is.”
Areas of the state, like western Ohio, had a lot of problems with bean pod mottle virus, and initial reports this year show seed quality to be outstanding.
Bean pod mottle virus causes reduction in seed quality through seed coat mottling and reductions in yield, by producing malformed pods that contain beans so dry they are unsuitable for harvest.
Aphid damage. Soybean aphid populations were high in northern Ohio counties this year, but researchers are unsure whether the insect or environmental stresses may have caused yield reductions in that part of the state.
The soybean aphid can transmit soybean mosaic virus, which produces similar symptoms as bean pod mottle virus. “The farther away from the northern counties we got, the lower the populations,” Hammond said. “But a lot of the areas with aphids corresponded with severe drought conditions, so it’s going to be hard to determine what is causing some of the yield reductions in those areas.”