FOZ DO IGUASSU, Brazil (DTN)--At the World Soybean Research Conference plant scientists from around the world agreed Asian soybean rust would continue to cut yields and that education is the most effective weapon in fighting the fungus.
During one presentation, agronomists from six countries outlined the outbreaks in their areas and their search for resistant varieties. Many countries have found varieties with partial, but not complete, resistance to soybean rust.
However, even if a resistant variety is found, the problem won't be solved completely, the scientists said. Resistance does not mean immunity. Resistance is an ability to keep yield loss at the lowest possible levels.
Zhan-hong Ma, agronomist at the China Agricultural University in Beijing, said in 2002-2003 over 8,000 germplasms were studied for rust resistance and only 64 were found.
Asian soybean rust was first discovered in China in 1934. Four different races of the fungus have been found in that country.
"Mainly today, the outbreak of soybean rust is located in South China," Zhan-hong Ma said. "Frequent cases [are] in Central China."
Soybean rust appeared in Thailand in 1973, after a new variety of soybean was introduced, said Srisuk Poonpolgul, from the Thailand Department of Agriculture in Bangkok. He, also, has been unable to find widespread resistance.
"After testing 125 soybean varieties, only a local one showed resistance," Poonpolgul said.
If left untreated, soybean rust could cut yields by 34 to 40 percent, Poonpolgul said .
"Our research indicated applying fungicide 35 days after planting as the most effective application," Poonpolgul said.
Clive Levy of the Commercial Farmers Union of Zimbabwe, said after studying soybean rust for six years, he thinks farmers and ag businesses need to work together to battle the fungus.
"I don't believe any one company can outdo another in trying to rid soybeans of this critically devastating disease," said Levy.
In Zimbabwe, research has shown farmers had the most success in controlling damage in rust infected fields by applying fungicide before the R-4 and R-5 stages of development are reached. Levy suggested applying fungicide three times for severe outbreaks and two times for marginal cases. Soybean growers in that country are encouraged to spray 50, 70, and 90 days after planting.
Farmers may need to develop a more aggressive attitude toward spraying, suggests Eve du Preez, a South African plant pathologist. "We are finding the farmers who raise soybean seed spray more aggressively than farmers raising soybeans in general," Preez said. Soybean rust first appeared in South Africa in February of 2001, causing between 10 and 80 percent yield loss. It most likely migrated from Zimbabwe.
Although Africa only produces 200,000 tons of soybeans annually, rust is affecting plans to expand that production.
"We have been making an effort to raise more soybeans and were doing a good job at it until soybean rust set us back," said Pat Caldwell, a South Africa agronomist.
Wilfrido Morel, a Paraguay agronomist, was the first person to find rust in South America, during the 2000-2001 crop year. "In untreated fields, we saw yield reductions of 60 percent from the rust," Morel said.
"One-hundred percent of Brazil is affected by rust," said Jose Tadashi Yorinori, spokesman for Embrapa, the Brazilian government's research corporation). "We are trying hard to get the word out to farmers about the need to spray fungicides."
Yorinori added, "In Sao Paulo state, there was a region that had yet to have the soybean rust--but they do now."
The threat of rust spreading into unaffected areas is increasing, Yorinori said, as cooler than normal conditions prevail.
Embrapa officials estimate crop losses from soybean rust could reach $1 billion. However, Yorinori was cautious about giving an estimate of the Brazilian crop size that takes into account rust, drought and wet conditions during harvest.
"The losses are unknown," Yorinori said. "We should know in about a month. A lot can happen yet."