September 25, 2012

Soybean Rust Could be a Big Problem in Mato Grosso in 2012/13

Author: Michael Cordonnier/Soybean & Corn Advisor, Inc.

State agriculture officials in Mato Grosso have already expressed concern that soybean rust may be especially bad this year due to the presence of the disease in volunteer soybean plants growing in the state. Normally by the time a new soybean crop is planted, the rust spores are no longer viable due to the volunteer soybean plants dying out during the dry season, but apparently, that has not been the case this year.

It had been thought that rust spores could only survive about 28 days without a living host plant such as a live soybean plant. Researchers in Mato Grosso have now determined that under the right conditions of heat and humidity the rust spores can remain viable for more than 40 days after the host soybean plant has died. This has alarmed researchers because that means that there will be live spores in the air when the newly planted 2012/13 soybean crop emerges in a few weeks.

The climatic conditions during the dry season that is just ending in Mato Grosso were ideal for the propagation of the rust spores. The last rainy season did not end until late in June which allowed spilled soybeans to continue germinating until July. Some of those volunteer soybeans are still alive and harboring the disease. Even if the plants have already died, the new research indicates that the conditions over the last several weeks have been conducive for the survival of the spores.

The problem of volunteer soybeans is not necessarily a problem out in the farmer's fields, but rather along the highways and near storage and transportation facilities. Technicians from the state department of agriculture inspected 2,800 properties during the 90-day soybean free period (June 15 to September 15) and they notified 300 landowners of the presence of live volunteer soybeans on their property and they levied 41 fines for not eliminating the soybeans in a timely fashion. Part of these inspections included along highways and near grain elevators and transportation facilities where 92% of the sites inspected contained live soybean plants and 85% of the plants were infected with soybean rust.

The problem is not a case of neglect on the part of the property owners for not eliminating the volunteer soybeans, but rather the nature of the way that soybeans are transported within the state. Many of the trucks that haul soybeans in Brazil are not grain-hauling trucks, but rather trucks designed for hauling dry goods that are used to haul gain instead. As a result, soybeans can be seen dribbling out the back of the trucks as they travel down the pothole-filed highways of Brazil. We have driven behind trucks in Brazil where soybeans were constantly dribbling out the back of the truck and hitting the windshield of our car. These spilled soybeans can accumulate all along the highway and germinate whenever there is sufficient rainfall such as this year. It is these volunteer soybeans along the highways that have officials so concerned.

The worst example of early rust infestations occurred during the 2004/05 growing season. During that year, the city of Primavera do Leste in eastern Mato Grosso became known as the "Rust Capital of the World."on During that growing season, the first case of rust was detected just 18 days after the soybeans had been planted and 13 days after the soybeans had emerged. That forced farmers to make repeated fungicide applications from the beginning to the end of the growing season. Some farmers even had to start applying fungicides before they finished planting all of their soybeans.

The 2004/05 growing season was just a few years after soybean rust had been detected in Brazil and the farmers and researchers were still trying to identify the best way to control the disease. They are now much better at controlling the disease, but an early onset of soybean rust could be very problematic for the soybean crop. Soybean rust is the most destructive disease that can affect soybeans and it remains a chronic problem for Brazilian soybean producers.