CHAMPAIGN, Ill. — Crop science experts say recent research shows early planting of soybeans no longer is leading to a measure of yield loss – at least in beans that have been planted around mid-April.

March or early April soybeans still show significant signs of yield loss and disease, said University of Illinois crops sciences professor Emerson Nafziger.

Given near-ideal weather conditions throughout most of the Midwest, producers have about 35 percent of the corn crop in the ground – second-fastest to the 2010 season – and a record 5 percent of the soybean crop already planted, according to the USDA.

Nafziger noted mid-April bean plantings are faring the best, recently. Yields declined slightly by early May, and by mid- to late May, losses were up to 0.3-0.4 bushel of delayed planting. By early June, each day of delay meant a loss of about half a bushel of yield per acre.

“We, and researchers in other states, had generally found that soybeans tended to suffer little yield loss from planting delays until after the middle of May, after which yield loss accelerated,” Nafziger said. “We now have evidence that waiting until some date in May to plant soybeans may not be necessary or even helpful to yields.”

Finishing corn planting and then starting soybean planting may be a good option, at least after mid-April, he suggested. The new research suggests early bean planting is most likely to help yields when conditions for high yields exist throughout the season.

But with early planting comes the continued risk of the fungus Fusarium virguliforme, or sudden death syndrome (SDS). Plant pathologist Carl Bradley noted SDS infects soybean roots very soon after planting.

The first signs of the disease are yellow splotches on the leaves that develop into interveinal chlorosis (yellow leaf tissue between veins that remain green) and then interveinal necrosis (dead leaf tissue between veins that remain green). The fungus also can cause root rot.

“In fields where SDS has been a historical problem, it is best to plant soybean varieties that have a high level of resistance to SDS,” Bradley said. “In addition, consider planting these fields with a history of SDS last.”

If there is enough water to start the germination process but not enough to get plants to emerge, seeds and seedlings often die, he explained. Thus, if soils have limited moisture, it may be better to wait until after rainfall to plant.

Nationally, soybean acreage for 2012 is estimated to end up at 73.9 million acres, down 1 percent from last year and down 5 percent from 2010, according to the USDA. Compared with 2011, planted area will be down or unchanged across the Corn Belt and Great Plains with the exception of Illinois, North Dakota, South Dakota and Wisconsin.

The top five-producing soybean states accounted for roughly 54 percent of all beans harvested in the United States last year. Iowa led all states with 466.1 million bushels harvested, followed by Illinois at 416.4 million, Minnesota with 270.3 million, Nebraska at 258.4 million and Indiana at 238.1 million.