May 19, 2021

"Soybean Free" Period starts in Parana on June 10th

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

In the state of Parana in southern Brazil, May 15th, was the last day a farmer in the state was allowed to harvest any soybeans. By June 9th, farmers and landowners must eliminate any volunteer soybeans that may have germinated in harvested fields, along the roadways, or in the vicinity of storage unites or transportation facilities. These volunteer soybeans can serve as host plants for the disease to survive from one growing season to the next. From June 10th to September 10th, no live soybean plants will be allowed during the "Soybean Free" period.

During the Soybean Free period, the state of Parana will send out teams of technicians in search of live soybean plants and the landowner will be notified if any live plants are found on their property. They will be given a grace period to eliminate the plants, but if they fail to eliminate the plants, they will be subject to fines.

The Soybean Free period has been shown to be an effective way of delaying soybean rust (Phakopsora pachyrhizi) from invading newly planted soybean fields. The earlier soybean rust enters a soybean field, the greater the potential for yield loss. Soybean rust is the most destructive disease of soybeans and if left unchecked, can cause losses of 80% or more.

According to data from the Consorcio Antiferrugen (Antirust Consortium) soybean rust costs Brazilian farmers an average of US$ 2.8 billion per year in control costs and lost productivity. Parana is one of the states most impacted by the disease and during the 2020/21 growing season, more than 100 cases of rust were confirmed in the state. This was the second most in Brazil after Rio Grande do Sul which registered 138 cases.

In addition to the Soybean Free period, other ways to help control the disease include: plant soybeans as early as allowed, plant early maturing soybean varieties, plant varieties with some level of resistance to the disease, and use appropriate fungicides.

For the last three growing seasons, the state of Parana has deployed a system of spore collectors across the state in what they call their Rust Alert system. The system can determine when the level of spores are high enough in a region to justify fungicide applications. In addition to determining the level of spores in a region, the system also takes into account when the crop starts to flower, which is when the disease generally starts to invade the plant, and if the environmental factors are favorable for the development of the disease. Without knowing the level of risk, farmers may be applying fungicides unnecessarily.

Researchers have determined that farmers who do not use the Rust Alert system generally apply three times more fungicide applications compared to farmers who do use the system.