Iowa Public Television


Scientists Search For A Solution To Soybean Rust

posted on July 22, 2005

Hurricane Emily blasted onshore this week in South Texas, causing widespread flooding and property damage along the coast. But it appears cotton producers in the Lower Rio Grande Valley escaped the damaging wind and rain associated with the storm. Texas is the nation's leading cotton-producing state and is on track for an excellent crop this year.

It was another tropical storm, Hurricane Ivan, which is thought to have brought Asian soy rust to American shores in 2004. That storm struck the Gulf Coast of Alabama and Mississippi, two of the states in the Deep South that have reported cases of soy rust.

But the spread of the crop-wasting fungus has been slow ... and scientists are using what time they have to study the plant disease and devise a battle plan. Nancy Crowfoot explains.

Scientists Search For A Solution To Soybean Rust Utilizing what is called a gene chip, scientists at Iowa State University in Ames, can look at 40,000 soybean genes at one time. They will study both the genes of healthy plants and those infected with Asian soybean rust... to identify the specific genes affected by the devastating disease.

Dr. Thomas Baum, Department of Plant Pathology, Iowa State University, Ames, Iowa: "We will look at soybean plants that are infected with the soybean rust fungus and assess gene expression changes over time as the disease progresses. The ultimate goal of our work is to use this information and devise novel tools against the disease."

Once the affected genes are identified, the bean could be genetically modified. A transgenic germplasm would be developed, which could be used to create a rust-resistant seed.

But it will be years before a new variety of seed is available for farmers to plant. In the meantime, the only weapon to fight Asian soybean rust is the use of fungicides & and education.

Soon after rust was discovered last fall, seminars were held to discuss identification and available treatment. The advice given:

-- Learn to identify the disease. The fungus begins as small lesions on the lower leaves of the plant. The lesions increase in size and change from gray to reddish brown on the underside of the leaves. Some say, soy rust in its early stages can resemble spider mite or brown spot.

--Learn about fungicides: their ingredients and their efficiency. Among the advice is, don't spray as a preventative measure unless rust is confirmed in your state this growing season. It is an expensive treatment.

Dr. Kurt Guidry, Louisiana State University AgCenter: "Look at two applications of fungicide along with application costs. You're looking at anywhere from $30 to $40 an acre in terms of additional production costs."

Last year, Brazilian farmers spent $350 million battling rust -- and said spraying immediately after detection is essential to cutting crop loss.

--Learn the critical times for scouting soybean fields. The plants are most vulnerable from the flowering to pod fill stages and scouting should be done on a daily basis. At other times during the growing season, fields should be inspected at least twice a week.

Dr. Monte Miles, USDA: "If you're scouting from your pickup truck you're never going to see soybean rust. It's not like aerial blight. You have to get out in the field. You gotta get down in the lower canopy and you really have to search."

--And finally, select soybean acreage carefully. Asian rust thrives in moist, humid weather between 68 and 77 degrees. Plants in low-lying, wooded or shaded areas are especially vulnerable.

But no matter the precautions and treatments, the potential for any sort of epidemic of Asian soy rust most likely will be determined by weather conditions and how the disease is treated where it is now. Found first in a Louisiana test plot last fal, the disease then spread to eight other states in the southeast.

There is worry that this summer's tropical storms moving through infected areas will spread existing rust spores. Rust has been discovered on kudzu, volunteer beans and few sentinel soybean plots in the southeast. But so far, there is just one 2005 report of soybean rust on a commercial soybean field ... and that was in Alabama.

Dr. Thomas Baum, Iowa State University: "The issue is the fungus will not survive the winter, so for it to be a problem up here it has to be introduced every spring or every summer anew. The weather conditions and the presence of the disease in the over wintering grounds in the south will determine how bad and how soon the disease will be occurring in Iowa."

It is too early to predict just how much of a problem Asian soy rust will be during this, the first planting season since the parasitic disease landed on U.S. soil.

While concern and nervousness are valid, Dr. Baum says, "don't panic." Soybean production still occurs worldwide even in countries where Asian soybean rust has been around since the early part of the last century. First discovered in the Far East, it arrived in the western hemisphere just a few years ago.

Brazil has fought the disease since 2001 ... and

despite losing 4.7 million metric tons -- or about 172 million bushels to rust -- the South American country continues to be one of largest producers of soybeans worldwide.

This should be hope enough that U.S. farmers and their soybean crop can also survive.

Dr. Thomas Baum, Iowa State University: "Brazil has been hit extremely hard since 2001, but they manage to survive. They obviously had to get ready in a hurry. We have the added luxury that we can draw from their experiences and they've been very helpful. There is definitely hope and soybean production will go on. Its just something else to deal with."

For Market To Market, I'm Nancy Crowfoot.

Tags: agriculture diseases farmers news research science scientists