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August 7, 2014

90-day Soybean Free Period helps to Control Spread of Rust in Brazil

Soybean farmers in Brazil and Brazilian scientists have made significant progress in controlling soybean rust, which is the most serious disease impacting soybean production in Brazil. One of the more important advances has been the adoption of a 90-day soybean free period during which no live soybean plants are allowed. In addition to a prohibition of actually growing soybeans during this period, any volunteer soybeans that may germinate must also be eliminated. If a landowner has been notified that live soybean plants have been found on their property, they are given ten days to eliminate the plants or face fines.

In the state of Mato Grosso do Sul for example, the soybean free period, which started in 2006, prohibits live soybean plants between June 15th and September 15th. According to a regional director of Embrapa, since the prohibition went into effect eight years ago, the number of cases of soybean rust in the state has fallen by 95%. In 2006 there were 613 reported cases of soybean rust in the state, but by the 2013/14 growing season, the number had fallen to just 31 cases.

In the cities of Dourados and Maracaju for example, there were 190 and 34 cases of rust reported in 2006 respectively, but during the 2013/14 growing season, both cities recorded only one case of rust.

The idea behind the soybean free period is to limit the spread of the rust spores from one growing season to the next. Soybean rust spores can survive without a host plant for approximately 60 days, so if host plants such as live soybeans are eliminated for a 90 day period, the chances of spores surviving from one season to the next is greatly diminished. The soybean free period is not the only reason for the advances in controlling the disease, but it is being given credit for a major part of the success.

When the disease first appeared in Brazil during the 2000/01 growing season, rust was sometimes found in soybean fields as soon as 30 days after planting. Today, the first cases of rust may not be detected until the crop is approaching maturity. The delayed appearance of the disease is being attributed in large part to the soybean free period.

Other factors that have contributed to the success in controlling the disease include: preventative fungicide applications and fungicides more targeted to controlling the disease, a much improved monitoring system that tracks the advance of the disease, more resistant soybean varieties, and the planting of more early maturing soybeans that are not exposed as long in the field to the disease.

The entire 90-day soybean free period is being reevaluated due to the increased planting of safrinha soybeans. This is the planting of two soybean crops back-to-back in the same field during the same growing season. Scientists are very worried that planting two crops of soybeans in the same field in the same year will allow diseases and insects to more easily spread from one growing season to the next.

The Brazilian Minister of Agriculture has been studying the issue and feels that some sort of prohibition on safrinha soybean production may be appropriate, but no firm action has been announced. Some proposals being discussed include starting the soybean free period earlier and extending it to 120 days or 150 days. The end of the soybean free period will remain on September 15th, so if the starting date is backed up to May 15th (120 days) or April 15th (150 days), that would essentially prohibit the possibility of planting a second crop of soybeans.