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December 29, 2011

Rust and Nematodes are Principal Pests of Brazilian Soybeans

Brazilian soybean farmers are hoping that their success against soybean rust last year can be repeated again during this growing season. Soybean rust is a devastating disease and if left unchecked, it can cause losses of up to 80%. During the 2010/11 growing season, the number of cases of rust reported in Brazil fell to the lowest level since the 2004/05 growing season and the amount of damage caused by the disease was 70% less than the previous year. Thus far this growing season, there have only been 15 cases of the disease confirmed in Brazil.

During the ten years that the disease has been present in Brazil, it has cost producers an estimated US$ 19.7 billion in lost production and chemical control costs. The correct application of fungicides can keep the disease under control, but multiple applications may be needed during the growing season. Other cultural practices that have been successful in controlling the disease has been the adoption of soybean varieties more resistant to the disease and the observance of the 90-day soybean free period (June 15 to September 15) that has been instituted in the majority of the soybean producing states in Brazil.

In the state of Mato Grosso, which is the largest soybean producing state in Brazil, the disease has cost producers an estimated US$ 9.2 billion over the last ten years. Thankfully, the disease was of minor importance in 2010/11 with only 50 confirmed cases in the state compared to 600 cases registered during the 2009/10 growing season. Thus far this growing season, no cases of the disease have been confirmed in the state.

While soybean rust receives most of the attention, the largest yield robbing pest in Brazilian soybean fields are nematodes, which are microscopic worms that feed on the roots of soybeans. While rust can be controlled with the proper use of fungicides, nematodes are much more difficult to control. Nematodes have become a major soybean pest principally due to the nature of soybean production on Brazil.

The majority of soybeans in Brazil are produced as a monocrops, which means that soybeans are planted in the same field year after year. The most effective way to control nematodes is to plant resistant soybean varieties and to rotate to other crops, but since most soybean fields are not rotated to other crop, the nematode population has been allowed to increase to yield reducing levels. Even if they did rotate to other crops, nematodes can persist in the soil for up to ten years.

Therefore, the most effective control measure is to plant soybean varieties that are resistant to the races of nematodes prevalent in the area, but unfortunately, the worm can develop resistance to the new soybean varieties about as fast as plant breeders can develop new varieties, so it is a never ending battle to control the pest.