Sep 14, 2015

Brazilian Scientists Worried about Soy Rust on Volunteer Soybeans

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

With the recent rains in Mato Grosso, scientists are worried that volunteer soybeans growing alongside of the state's highways may be harboring soybean rust spores that could move into the newly planted soybean crop. Scientists and technicians from the state's animal and plant protection bureau fanned out across the state last week and they found live soybean plants in the municipalities of Campo Novo do Parecis, Vera, Claudia, Feliz Natal, and others.

Rains earlier in July and August allowed some of the soybeans that spilled out of trucks to germinate alongside the highways and those soybeans are now in their reproductive phase which is the most sensitive time for rust attack. Landowners are required to eliminate volunteer soybeans on their property during the soybean-free period, but the soybeans growing along the highways are generally not eliminated.

Scientists are also worried that rust spores could blow into the state from neighboring Paraguay and Bolivia where there has been much less attention paid to controlling soybean rust. Those countries do not have a soybean-free period similar to Brazil. In fact, in Paraguay there are significant amounts of soybeans grown back-to-back in the same field during the same growing season. The first crop is planted in August or September and harvested in December or January. Farmers then quickly plant the second crop of soybeans which are then harvested in May or June. This back-to-back production allows for the disease to continue to be active for an extended period of time.

Scientists are also worried that the practice of planting safrinha soybeans can force the disease to more quickly develop resistance to commonly used fungicides. Some of the chemicals that are currently being used in Brazil have already lost nearly half of their effectiveness. That is why safrinha soybean production has been prohibited in the state of Mato Grosso starting with this growing season. Scientists are also telling farmers to rotate their chemical use as a way to slow down the development of resistant rust spores.

Farmers in Mato Grosso will be allowed to start planting their 2015/16 soybean crop on September 15th with the expiration of the soybean-free period in the state. This soybean-free period was established about 10 years ago as a way to slow the spread of soybean rust from one growing season to the next. Originally, the soybean-free period was from June 15th to September 15th, but the period has now been lengthened from May 1st to September 15th. It was lengthened for the specific purpose of prohibiting farmers from planting two crops of soybeans back-to-back during the same growing season. Thus far, Mato Grosso is the only state in Brazil to have lengthened the period, but other states are also considering doing the same thing.