Soybean diseases ripped off an estimated 516 million bushels from U.S. growers in 1998 - worth about $2.8 billion. It was over $3 billion in '97 because of higher soybean prices.

That's about a $3 billion loss on a total crop worth roughly $16 billion. The loss estimates were compiled from a national survey of plant pathologists, funded by United Soybean Board checkoff dollars.

Worst of all, say plant pathologists, many growers don't even know they have a problem.

"In Missouri, and I think it's probably worse as you move north into better ground, we deal with what I call the 40- or 45-bu syndrome," says George Smith, a University of Missouri extension plant pathologist who also farms.

"We run into farmers who say, 'I got 40 or 45 bu/acre, and I don't have any problems.' Well, we have data that show they should be getting 50, 55 or 60 bu/acre," Smith says.

"It's a hard nut to crack to convince these guys they really have a problem because generally 45-bu beans look fine, or at least okay. Often, they don't show any obvious symptoms of disease. But the yield loss may be there just the same. You can bet on it," Smith points out.

Many better growers, however, do complain that their yields have stalled out; that seemingly some mysterious "yield lid" has descended on their soybean fields.

The real culprit: a disease buildup that has clamped a lid on the higher genetic potential of new varieties - leaving yields static.

Many growers are, of course, getting bin-busting yields. But here are some eye-opening examples of 1998 disease devastation.

"We estimated last fall that 30% of the soybean fields in Illinois were affected with sudden death syndrome (SDS)," says Oval Myers, a Southern Illinois University scientist. "In some counties, though, more than 50% of the fields were affected. There were even parts of some fields with no beans on any of the plants."

SDS is a spreading and increasingly nasty disease challenge. Although it robbed 33 million bushels from U.S. soybean growers last year, it's not the heavyweight of yield stealers. Soybean cyst nematode (SCN) wears that crown. According to the national survey of plant pathologists, conducted by Allen Wrather, another University of Missouri plant pathologist, SCN stole an estimated 219 million bushels in 1997 and 279 million in 1998.

The second-place yield robber will probably surprise many because the disease has been around since Moby Dick was a minnow. It's phytophthora root rot (PRR), which swiped over 42 million bushels in 1998, according to Wrather.

The big reason, despite the fact that hundreds of tolerant or resistant varieties have been developed, is that this disease is slipperier than an eel. It develops new races to do an end run around the resistance offered by varieties that have been used heavily against it.

"We've gone from 25 races just a few years back to 53 that have now been described. That's one big reason why PRR continues to be a major disease in soybeans," notes Missouri's George Smith.

Sclerotinia stem rot (white mold), affecting primarily the northern Corn Belt, wreaked havoc in 1997, stealing over 35 million bushels. In 1998, it was tamed only by less-favorable weather for the disease during the critical time period, and took a little over half as much - 18.7 million bushels.

Brown stem rot (BSR), a northern soybean disease, was also less profit-wrecking in '98, stealing 14.7 million bushels, compared with 24 million bushels in '97. But in '96, a favorable year for the disease, it caused losses of 30.8 million.

Charcoal rot, a disease of more southern climates, ripped farmers to the tune of 38 million bushels of soybeans in '98. Hot, dry weather in the affected areas drove the severity and spread.

Sometimes two or more diseases team up to amplify the yield-stealing effect.

"Nematodes, along with any other disease problem, can knock the socks off soybean yields," notes Wrather. "It's sort of like two times two equals five or six instead of four."

As long as most Corn Belt soybean growers are stuck with a corn-soybean rotation, the disease yield lid challenge will get tougher, not easier, scientists agree. It will take top management to tame the ravages of disease and put yields up where they should be.