February 6, 2013

Increased Amount of Rust Worries Brazilian Soybean Producers

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

Farmers in Rio Grande do Sul are worried about the amount of soybean rust being identified in their soybean fields. Embrapa has confirmed 78 cases of the disease in the state, which is the most of any soybean producing state in Brazil. The state of Parana has the second most cases at 71.

Although January had been relatively dry in the state, the month of December was very wert, which aided the spread of the disease. The rust spores are very light and easily dispersed by the wind. The ideal conditions for the spores to infect a soybean plant are temperatures near 24 degrees Celsius (76 F) and six hours of wetness. Soybeans can be infected at any time during their life cycle, but they are especially susceptible during flowering. Conditions are more favorable for the disease when the canopy closes and humidity levels remain high at the bottom of the canopy. If left untreated, the disease can defoliate the plant prematurely cutting short the pod filling process and resulting in lower yields

The recent wet conditions in Mato Grosso are also contributing to more cases of the disease being reported in the state (63). Even the harvesting of the early maturing soybeans can make the disease worse. The physical process of harvesting the soybeans can disperse the spores to nearby fields that may still be setting pods and filling pods.

Disease officials in Mato Grosso are also worried about the possibility of farmers planting a second crop of soybeans after they harvest their first soybean crop. The original soybeans were planted later than normal in October and now wet weather is delaying the harvest of the soybeans even further, leaving little time to plant a second crop of corn. Instead of risking a second crop of corn, some farmers are planting a second crop of soybeans instead that will be harvested before the 90-day soybean free period starts on June 15.

Agronomist are warning the farmers contemplating planting back-to-back soybeans to be prepared to start applications of preventative fungicides early in the crop's life cycle. Under a worst case scenario, the second crop of soybeans might require up to five applications of fungicides to keep the disease under control.