Many growers still not paying attention White mold did not wreak the havoc in 2000 that it did in, say, 1997. Weather didn't favor it. And a new educational weapon, a white mold Web site, has been added in the battle against the disease.
The new site, based out of the University of Wisconsin, has been established by the White Mold Coalition. It consolidates research information and management strategies from 10 North Central states.
That's the battleground where sclerotinia stem rot, commonly called white mold, is found. Farther south, the disease can't handle the higher temperatures in July and August.
The Web site address: www.plantpath.wisc.edu/ncsrp whitemold/
Fortunately, many farmers have adopted the recommended strategies to tame white mold, which probably also helped reduce the incidence and losses to the disease last year.
That's the good news. The bad news? Many farmers are still flunking the management strategies course needed to squeeze down losses.
"From what I heard from many crop consultants, I think a high frequency of high-severity cases was the result of farmers not paying attention to variety selection to fight the disease," notes Craig Grau, a University of Wisconsin plant pathologist. "I heard from several crop consultants who expressed frustration that their clients just ignored that aspect because they didn't think it made any difference, which is dead wrong."
By contrast, some growers who encountered heavy yield losses in drilled beans in the 1990s, when it was often cool and damp during the critical bloom and early pod-set period, have switched back to 30" rows.
That's a mistake, Grau believes. And several White Mold Coalition plant pathologists agree, including the University of Minnesota's Jim Kurle and Ohio State University's Anne Dorrance.
"I think this past year or two that growers who went all the way back to 30" rows as a protection against white mold have really hurt their yield potential," says Grau.
He maintains that, except in areas especially favorable to white mold, drilled beans in combination with the best partially resistant varieties will still net more yield than will 30" rows. High-risk areas include river valleys, low pockets and near shelterbelts, which often harbor fog and heavy dew because air movement is restricted.
A good compromise would be to plant the best partially resistant varieties in 15" rows, which offer slower canopy closure but still maintain the narrow-row yield advantage, Grau says.
"We had one year of research results that showed plant population made a bigger difference than row spacing," notes Kurle. "I recommend backing off those really high plant populations in narrow rows because reducing canopy density helps control white mold.
"I wouldn't recommend that anybody go back to 30" rows to control white mold if they're now in 15" or drilled beans," Kurle adds. "There are too many other variables having to do with yield, weed control and so forth favoring narrow rows."
Dorrance agrees. "We don't recommend going back to 30" rows for white mold control, because of their lower yield potential," she says. "And we find comparable yields in the 7" and 15" rows in white mold areas."
The white mold Web site, says Dorrance, carries recommendations for controlling white mold for the North Central region, articles concerning specific states, additional Web links with state fact sheets, stand-alone research reports and also end-of-year reports from states.
In short, it has the latest and best recommendations available concerning white mold control, she says.
So what are the bottom-line recommendations for white mold control from these scientists?
- For fields with a history of white mold problems, or where it's newly discovered, study variety test results and pick the best resistance you can in a variety that otherwise fits your program - regardless of row width. The list of varieties with partial resistance is getting longer and longer, because all major breeding companies are breeding for better white mold resistance.
- Avoid ultra-high plant populations that can produce denser canopies and restricted air movement during the bloom-pod set stages.
- Consider later planting. Generally, the later the planting date, the less white mold will develop - but you may sacrifice yield unless white mold hits hard that year.
If you haven't encountered white mold yet - and some farmers haven't - scout fields, especially in August if conditions are cooler and wetter than normal at flowering. See the photo for symptoms. Small black sclerotia develop on or inside infected stems. And a white cottony substance often develops on external stem tissue.