Farmers advised to watch for soybean fungus

Sussex County may be renowned for poultry, but farmers grow a hill of beans here, too.
According to the U.S. Department of Agriculture (USDA) statistical survey for the state (found at, soybeans are planted to more acres in Delaware each year than any other field crop.

They consistently rank at or near the top for cash production, depending on markets, growing conditions, pests — and this year, a fungus called “Asian soybean rust.”

According to Tracy Wooten at the University of Delaware Cooperative Extension (Georgetown), the fungus had come to the U.S. last year, during hurricane season.

“It’s been around in other countries — people knew it was going to be here eventually,” she said. “The Department of Agriculture people have been keeping an eye out.”

Wooten speculated that Hurricane Ivan might have blown soybean rust spores north from the equatorial zone. The fungus was discovered in the southern states late last year.

Derby Walker, a longtime educator at the Cooperative Extension (recently retired), said the agricultural community was still trying to determine what the impact would be.

“This is a new issue to us and we are in a learning mode, but we have to be prepared in case this potential problem becomes a problem in 2005,” he said.

As Walker pointed out, soybean rust needs three things — the fungus itself (it doesn’t “over winter” here), a host (the soybeans) and the right environmental conditions.

“Until we know where it will survive the winter to be blown up here, we don’t know when or if it will arrive,” Walker said. “We also have to have the right weather conditions for it to be able to enter the plant and cause a disease problem.”

Cooperative Extension’s Bob Mulrooney, a plant pathologist, has posted information about the fungus at

According to the Web site, spore germination requires six hours of moisture within a temperature of 59 to 82 degrees.

Rust spores infect leaf cells — not the seeds (beans, that is). Therefore, soybean rust poses no health threat to either humans or animals.

As Walker pointed out, the fungus appeared so late in the 2004 that it didn’t do any damage. “It has to arrive here in time to cause yield loss to justify treatment,” he said.

“It is way too early to decide if and how big of a problem it will be for us.”

According to Wooten, “People just need to be prepared — it has a very good chance of coming here.

“The key here is, we have the fungicides,” she said. “At some point, it sounds like farmers will have to do at least one preventative spray.”

In the meantime, information had gone out to the growers, including fact sheets that will help them distinguish soybean rust from other diseases.

Wooten said they were working on the assumption that the fungus might reduce yield by between 10 and 30 percent.

There are no disease-resistant varieties of bean yet, and switching to another variety wouldn’t work either — limas and snap beans are susceptible, too.

(Incidentally, Delaware is number two in baby lima production for the country, according to Walker).

“This is a new issue to us and we are in a learning mode, but we have to be prepared in case this potential problem becomes a problem in 2005,” he said. “It will develop first in the southern states, and we will learn from their experiences.”